Limnology 2nd sem (full sylabus)

POWER RANGERNOTES LIMNOLOGY
1
Limnology
1.1.1Introduction
Civilizations have depended on water bodies such as lakes, reservoirs, rivers and wetlands. Water is essential
not only to sustain human life but also to support the activities that form the basis for thriving economics.
Though the water resources are essential to human societies who could pollute and degrade and limiting their
beneficial uses. Agriculture, mining, urban development and other activities can pose risks to freshwater
bodies and hence steps have to be taken to reduce these risk factors.
Risk analysis requires knowledge of how human land use affects physical, chemical and biological characters
of the aquatic systems. One of the critical areas required to understand how human actions and natural
processes affect lakes, reservoirs, rivers and wetlands is the science called Limnology. It is a multidisciplinary
science that integrates the basic sciences (Biology, Chemistry, Physics and Geology) in order to study inland
waters as complex ecological systems.
Definition
The term Limnology is derived from Greek word; Limne means lake and logos means knowledge. Limnology
is often regarded as a division of ecology or environmental science. It is however, defined as “the study of
inland waters” (running and standing waters fresh and some times saline; natural or man made). This includes
the study of lakes, ponds, rivers, reservoirs, swamps, streams, wet lands, bogs, marshes etc. Hence, it is
commonly defined as that branch of science which deals with biological productivity of inland waters and
with all the causal influences which determine it (Welch, 1963).
Biological productivity, as used in this definition, includes its qualitative and quantitative features and its
actual and potential aspects. Under the term inland waters are included all kinds or types of water – running or
standing; fresh, salt or other physicochemical composition which are wholly or almost completely included
within the land masses. Causal influences involve various factors – physical, chemical, biological,
meteorological etc which determine the character and quantity of biological production.
History
The term Limnology was coined by Francois-Alphonse Forel (1841 – 1912) who established the field with his
studies on Lake Geneva. Interest in the discipline rapidly expanded and in 1922 August Thienemann (a
German Zoologist) and Einar Naumann (a Swedish Botanist) co-founded the International Society of
Limnology (SIL, for originally Societas Internalis Limnologiae). Forel’s original definition of limnology,
oceanography of lakes was expanded to encompass the study of all inland waters.
Welch (1935) conceived the problem of “Biological productivity” as the central theme of Limnology. He
defined Limnology as that branch of science which deals with all causal influences which determine it.
According to Schwoerbel (1987), Limnology is the science of inland waters viewed as ecosystems together
with their structures, materials and energy balance. Kiihnelt (1960) considered limnology as a sub set of
ecology along with “Oceanography” (which is concerned with marine ecosystem) and “Epheirology” (which
deals with terrestrial habitats). In short, Limnology is the study of all aquatic systems including lakes,
wetlands, marshes, bogs, ponds, reservoirs, streams, rivers etc. with regard to their physical chemical and
biological characteristics.
In addition to the above, certain other terms, like Hydrobiology, Freshwater Biology, Aquatic Biology,
Aquatic Ecology etc, are sometimes loosely used as synonymous to the word 'Limnology'. But, most of these
terms are names under which a diverse variety of subject matter is included and only a part of it is
limnological in nature.

2
1.1.2 Development ofLimnology
Initiation of works in the field of Limnology could be traced back to Aristotle (384-322 BC) which consisted mostly of
strange mixtures of facts and fiction with little scientific value followed by observation of certain conspicuous
freshwater phenomena. However,significant contributions of strictly limnological nature began to appear about a
thousand nine hundred years after Aristotle with the description related to habitat, habit and life history of certain fishes,
insects and aquatic macrophytes. But, most of these were isolated accumulation of correlated observations, few of which
could be used by modern limnologists mostly for historical purposes.
Since the initiation of optics with Euclid (2000 BC) and later with the invention of microscope, there has been
significant development in the field of aquatic biology and limnology because it has not only opened the door to the
whole world of microscopic organisms, but also provided with a new and effective means of studying the various higher
types of life in water. This was followed by description of minute aquatic organisms by Anton Van Leewenhook (1632
– 1723), the pioneering classification of microscopic organisms by the Danish biologist, Otto Friedrich Muller (1786),
publication of the Treatise, “Infus Animalcules” by Ehrenberg (1838) which marks the beginning of those advances in
knowledge which occurred in the 20th century.
Peter Erasmus Muller is credited with laying the foundation stone of limnological study. Anton Fritsch could be
considered as the pioneer in lacustrine limnology for his work on lakes in the Bohemian Forest and F. Simony (1850) is
regarded, sometimes as the founder of Limnology for his discovery of thermal stratification. However,it remained
practically everything for F.A. Forel (1841- 1912), a professor in the University of Lausanne, Switzerland, to recognize
the realbiological opportunity of lake investigations and the science of limnology is indebted to him for his
comprehensive vision and complete anticipation about the future of this subject. He is regarded as the Founder and
father of Modern Limnology for his 110 publications (Chumley, 1910). It was he who took the decisive step forward
from hydrobiology to limnology through his investigations in Lake Geneva, not only from the biological point of view
but also from physical and chemical stand points, thereby formulating the concept of lake types. In addition the design
of his first programme for limnological investigations in freshwater and its subsequent execution turned out to be a
model for future researches.
Forel’s work paved the way for establishment of Limnological Society in 1887 as a component of Swiss Naturalhistory
Society (in order to promote limnological works) and later the International Commission of limnology was established
in 1890). In brief, the History of limnology could be dated back to approximately 100 years. Although certain
preliminary studies has been done on the habits, nutrition, movement, behaviour etc.,on certain aquatic organisms by
different workers during the 17th and 18th centuries, these were mostly hydrobiological works and not limnological.
True studies on the relationship of biota to freshwater could be treated as initiated from Junge (1885) and Forbes (1897)
who were the first to treat the native waters as microcosm.
Gaarder and Gran (1927) made pioneering attempts at measuring the photoautotrophic production (primary production)
by quantitative determination of oxygen produced during photosynthesis. Later the direct measurement of carbon
assimilation in the water bodies was achieved in 1952 using radio-carbon method (Steemann and Nielsen, 1952). The
estimation of trophic dynamics concept having regard to the biomass, material turn over and energy transport along the
food chain by Lindeman (1942) not only revolutionized the field of general ecology, but also gave a new direction to
Limnology (Cook,1977).
Early freshwater investigations
In 1870, Simson, published a short account of the deep water fauna of Lake Michigan. Smith and Verrill (1871) made
deep water dredging in Lake Superior and published on the invertebrates collected. In 1886, the Allis Lake laboratory, a
privately supported institution and said to be the first freshwater biological station in America, was established at
Milwaukee, Wisconsin, but its life was brief and none of its work was concerned with the general biology of the Great
lakes. In the meantime, interested workers were giving attention to some of the smaller inland lakes. Forbes made a
study of certain high lakes of the Rocky Mountains and published only on biological information concerning lakes in
western United States. During the decade of 1890 -1900, important freshwater biological stations have been found viz,
(1) the University of Minnesota at Gull Lake,Minnesota, 1893; (2) the University of Illinosis on the Illinosis River,
1894; (3) the University of Indiana at Turkey Lake, Indiana, 1895.
The stimuli of scientific interest and of the necessities of public health brought about the initiation of systematic surveys
of water supplies and of water systems in general, the Massachusette State Board of health taking the lead in about
1887. Subsequently, similar work was undertaken by various municipal and government departments, all of which

3
contributed, directly and indirectly to the sum total of limnological information. Phenomenal progress of the general
subject of ecology inevitably had a constructive influence on limnology and because of its many ramifications
limnology has likewise profited from simultaneous advances of other sciences.
1.2.1 Inland waters
The inland waters which include both fresh water masses and estuarine waters of varying salt content are clearly
distinguishable from the salt waters of the oceans. The inland water masses are discrete and being isolated within the
specific land area,acquire the characteristic chemical composition of the land, by exchange between soil and water. The
oceanic water on the other hand is open and mixing together by wind action and currents and therefore more
homogeneous in chemical composition. However,the land water exchange is limited to coastalareas. The estuarine
waters are mixtures of sea and freshwater,but with the higher content of salts in the sea water (150 – 200 times that of
freshwater), are dominated by the sea water effects.
According to Hutchinson (1959), limnology is the large variety, individual and groups of inland water bodies, the
diversity being caused by the diversity of their origin as well as by the diversity of their chemistry and biology.
Types ofinland water
Frey (1960) has classified inland waters in three different ways viz, depending on whether the water is stationery or
flowing, depending on whether the water mass is natural or artificial and permanent / temporary.
I a. Flowing waters (Lotic waters)
These include creeks,streams and rivers mentioned in that sequence because of their sequence of succession also in the
same order, through the natural processes of lengthening and widening of running waters. In these,there is continuous
current of water in one direction. The organisms inhabiting these waters have complexity of adaptation towards the
increase in water current speed. It includes all forms of inland waters in which the entire body of water moves
continuously in a definite direction. The sequence of genesis is brooks, rivulets, channels and rivers.
b. Standing waters (Lentic waters)
Here,water current is not a major ecological factor; unlike in the lotic series lakes, ponds and swamps form the lentic
series. The sequence indicates the natural evolution of water masses as well lake may either be productive or non-
productive, when they are referred to as eutrophic or oligotrophic respectively. It includes all forms of inland waters –
lakes, ponds, swamps and their various integrades in which the water does not flow continuously in definite directions.
Essentially, the water remains standing, though a certain amount of water movement may occur, such as wave action,
internal currents or flow of water in the vicinity of inlets and outlets.
The sequence of genesis is as follows Lake – pond – swamp.
a. Natural bodies ofwater
Certain parts of the world are endowed with an abundance of natural waters serving human needs.
b. Artificial bodies ofwater
According to man’s needs water bodies are created artificially. It includes ponds, wells, tanks reservoirs etc.
i. Ponds
In India, even from ancient times, large ponds and wells exist serving for drinking water and also for irrigation purposes.
Types ofponds
Based on seasonalduration ponds can be classified into two types.
1. Temporary ponds
2. Seasonal ponds
Temporary ponds divided into three types,
1. Vernalponds: Water exists only in spring season.
2. VernalAutumnal pond: Water exists in those ponds during spring and autumn and they dry in summer.
3. Aestival ponds: Water persists in these ponds throughout the season but it freezes during winter.
Permanent ponds
Water persist in these ponds throughout the season but it freezer in winter.
i. Reservoirs
Rivers are blocked and reservoirs or artificial lakes are developed. These serve in generating hydroelectric power,
irrigation, fish production and recreation. These also help in flood control.

4
ii. Tanks
In India there are both perennial and temporary tanks. There are some in which water remains for 6-9 months duration,
called long seasonal tanks and in some, water remains for less than 6 months, referred to as short seasonal tanks.
III a. Permanent waters
In most parts of the world where there is precipitation exceeds,the evaporation and seepage loss the waters in rivers,
lakes and ponds and are termed as permanent waters.
b. Temporary waters
Evaporation loss of water is more than the precipitation gains, as in all arid areas of the world, the water bodies dry up
usually during summer. In high latitude (30-50o), when the area is desert the rivers and streams drain into permanent or
temporary lakes. These lakes have salt differing from that of sea,the salt washed down to the lakes being predominantly
potassium and sodium carbonates and magnesium and sodium sulphates and not sodium chloride. By evaporation at
times salt concentrations in these waters exceeds that of the sea. (eg. Great salt lakes and Dead sea). The salt
concentration of Dead sea is so high that there is no life in it.
1.2.2. Distribution ofinland waters
Inland waters cover less than 2% of the earth’s surface,approximately 2.5 x 106 km2. About 20 lakes are extremely
deep (in excess of 400 m). A significant portion of the world’s freshwater is contained in lake. Some regions are very
generously supplied with lakes and streams particularly those regions once subjected to ancient glaciation. Canada and
northern United States possess an immense supply of lakes, among them the Great lakes, which constitute the greatest
body of freshwater on the globe. Portions of Europe are also noted for their generous supply of lakes and streams. In
certain regions, disappearance of inland waters during the dry season forms the basis for special biological phenomena
resulting from the intermittent character of the environments.
In India, most of the wetlands including flood plain wetlands are situated in the eastern parts of the country whereas,
reservoirs and tanks have been created mainly for irrigation are distributed throughout the country. Large rivers and
streams are well distributed in the northern and eastern region of the country. However,southern regions of the country
also have a good number of inland waters. Many of them are seasonalin nature.
Dynamics of Lotic and Lentic environment
In the lotic series, the tiny rivulet gradually deepens, widens its bed, and cuts back at its head, thus in time extending its
length and increasing its cross section to that size which justifies the designation of brook. This process continues by the
same general type of action, ultimately producing a creek and then finally a river, with all of the integrating conditions
produced in such a gradual transformation.
Faunas occupying each of the different environments must accompany these migrations or become adapted to the
gradually altering conditions or they will become extinct. These environmental migrations are very slow, in point of
time, and give ample opportunity for the characteristic organisms of particular environments to make the necessary
responses. The ultimate fate of any lotic series is the degradation of the land is the reduction of its bed to base level.
In the lentic series,natural processes work toward extinction, mainly by the gradual filling of basins.
Lake –> Pond –> Swamp
In larger lakes, natural filling takes much longer time, even many centuries also hence the filling is primarily due to :
• Wind blown materials such as dust, sand and debris of various sorts.
• Sediments brought into a lake by inflowing streams and by incoming run-off water as it flows down adjacent land
slopes.
• Wave action, cutting away exposed shores and depositing eroded material in lake basin.
• Plants, particularly the higher aquatic plants which grow in shallow water,produce deposits of organic matter.
• Accumulating remains of animal life especially shells.
Not all lakes become extinct by filling alone. Other process also contributes to this for example an outlet may cut down
its level at the point of exit from a basin, thus gradually draining the lake.
These stages in the extinction of standing waters result in a more or less definite, predictable ‘evolution of environment’
in the long run has a profound influence on the history and fate of lake organisms.
Running waters (Lotic series)
There are many different kinds of running waters,severalof them occurring, inter-connected, within a single drainage
system. The range covered within the series includes small trickles and seepages,ditches, larger fast flowing streams

5
and rivers, large slow flowing rivers and canals.
The flow characteristic of any running water system are also closely connected with the geology, notably in the control
exerted by the nature and structure of rock and soil formations, and also in the relationship between the amount of
ground water and surface water flowing through the system. The basic flow pattern depends largely on the nature of this
relationship.
Most of the water on the earth is in constant circulation within what is known as ‘hydrologic cycle’. The energy utilized
within the cycle comes mainly from the sun. Water evaporates from both land and sea to be re-precipitated, usually
somewhere else. On most part of the land, precipitation exceeds evaporation, and run off towards the sea occurs.
Difference between running water and standing water
• Current : Unidirectional main current is found in running water but not in standing water.
• Depth: It is small in running water,more in standing water.
• Condition of gradient from source to mouth : In running water,physical, chemical conditions usually change from the
source to the mouth and the difference in many factors may be great between those extremes,but it is more
homogeneous in standing water.
• Water of the basin: Running water systems are very shallow and have long, complex narrow channels, but standing
water reach great depth, have broad basins.
• Permanent removal of eroded and transported materials: Constant erosion is common in running water and materials
so removed are transported to distance. Erosion occurs in standing water,but it is rarely severe,eroded materials and not
carried far away but remains within the same basins.
• Absence of prolonged stagnation: Consequence of erosion and deposition, most of the running waters tend to increase
the length of their channels with age. In standing water materials constantly being deposited tend to fill in the basin.
• Physical factor: It is more important in running water and standing water.
• Basic food materials: Most running water manufacture themselves little basic food, but depend on the contribution
from the surrounding land than the standing water.
1.3.1. Ponds, lakes, streams, river
Ponds:
Ponds are defined as small, shallow, inland standing water bodies, where rooted plants can grow over most of the
bottom. Ponds are mainly of three general classes,they are :
i. Those which represent the pond stage in the extinction of previously existing lakes
ii. Those whose basins have never been large or deep (not preceded by a lake) but or for some special reason, have
persisted in the pond stage and
iii. Those whose basins are the results of man’s activities (excavations, quarries, impoundments, etc.)
Natural process alone are constantly forming new pond basins (cut-offs from streams solution basins, beach ponds, and
many others), some of which are never more than temporary ponds from the beginning; others qualifying as permanent
ponds at least for a period in their existence.
Classification ofponds
With respect to seasonal duration, ponds are divided into two general classes
a. Permanent – those which contain some water the year round and
b. Temporary – those in which the basin contains water at certain times or seasons and becomes dry at others.
Those which occur for a limited period in spring are called Vernal ponds
Those which contain water in spring, dry up during summer, and again contain water in the autumn are called Vernal
autumnal ponds and
Those which contain some water throughout the open season but freeze to the bottom in winter have been called
Aestival ponds.
Other classifications ofponds are as follows
Natural ponds
These are perennial shallow water bodies. When a stream shifts its position it leaves behind an isolated body of standing
water which forms the "Ox-Bow" pond. In limestone regions where depressions are formed due to the solution of the
underlying strata,the water gets accumulated either by flood water or rainfall and natural ponds are formed. Sometimes

6
the last remnant of a lake whose basin has become filled progressively by sedimentation in course of time is transformed
into a pond.
Artificial pond
Most of the fish ponds are semi artificial ponds. Some are constructed by erecting dams across a stream or basin and
their water level can be regulated by inflow and drainage where pisciculture is practiced. Fish pond is a shallow body of
water that can be drained completely. It is often supplied by running water,but also by spring, ground or rain water.
Pools or Temporary Ponds
They occur in depressions in the ground either at the margin of glaciers where they fill with melt water or in the vicinity
of river bed, after the floods have receded. The water thus collected usually is very shallow and measures maximum to a
few feet only. Also prolonged rainfall may form temporary small pools. All these pools dry up in some part of the year,
and as such organisms in these habitats must be able to survive in a dormant stage during dry periods and be able to
move in and out of the pools.
General Characteristics ofponds
• Ponds are small, shallow standing water bodies.
• They have calm water
• Have more vegetation
• Growth of plants can also found at the bottom
• They have outlet streams
• The movement of water is minimum
• They have slight wave action
• The average depth of water is 8 – 10 feet
• The temperature of the pond more or less changes with that of atmosphere
• Light penetrates up to the bottom
1.3.2. Lakes
Forel (1982) defined lake as a body of standing water and occupying basin and lacking continuity with the sea. He also
defined pond as a lake of small depth, and a swamp has been defined as a pond of small depth and occupied by rooted
vegetation. Carpenter (1928) formulated that the true difference between lake and pond is depth and not area
accordingly a pond is a quiet body of water where floating vegetation extends to the middle of basin in which the biota
is very similar to littoral zone of lake.
Lake Morphology
The shape of a lake basin is largely determined by its mode of origin. The depth and contour of lake bottom can be
determined by lowering a weighted line or much more quickly with an echo sounder. Physical structural components of
lakes include their shape, distribution of light, distribution of heat,and movement of water. The hydraulic retention time
(time required for all the water in the lake to pass through its outflow) is an important measure for lake pollution studies
and calculations of nutrient dynamics. The hydraulic retention time is mainly determined by the interplay between
inflow of water into the lake and the basin shape.
Lake Zonation
The following depth zones are recognized in lakes:
a. littoral zone extends from the shore just above the influence of waves and spray to a depth where light is barely
sufficient for rooted plants to grow.
b. photic (euphotic) zone is the lighted and usually well-mixed portion that extends from the lake surface down to
where the light level is 1% of that at the surface.
c.aphotic zone is positioned below the littoral and photic zones to bottom of the lake, where light levels are too low for
photosynthesis. Respiration occurs at all depths so the aphotic zone is a region of oxygen consumption. This deep, unlit
region is also known as the profundal zone.
d.compensation depth is the depth at which rates of photosynthesis and respiration are equal.
e.sublittoral zone,which is the deepest area of plant growth, is a transition between the littoral and profundal zones.
f.pelagic zone (limnetic zone) is the surface water layer in offshore areas beyond the influence of the shoreline.
Boundaries between these zones vary daily and seasonally with changing solar intensity and transparency of the water.
There is a decrease in water transparency with algal blooms, sediment inflows from rivers or shore erosion, and surface
waves.

7
1.3.3. Streams and Rivers
A. STREAMS
Introduction
Streams are zones where a rapid flow of shallow water produces a shearing stress on the stream bed, resulting in a rocky
or gravel substratum covered by fully oxygenated water. Streams may vary in size from tiny rivulet to rivers. As time
goes the stream may develop into river or increase its size, whereas the size of reservoirs decreases as time passes. They
are more numerous in regions of abundant rain fall. They are temporary or permanent. Streams are closely linked to
their watersheds. The productivity of streams is often dependent on terrestrial bases,grasses and other debris. The
allocthonous materials contribute most of the food and energy to the organisms in the stream. Benthic invertebrates like
insect larvae constitute the invertebrate fauna. True plankton are almost absent in streams, and are common only in deep
slow moving stretches of rivers. All biota in streams are influenced by the unidirectional current.
Physical conditions
The annual change in stream temperature is 10 to 20°C. Although large rivers do not change in temperature very much
on a daily basis, a small unshaded stream may heat up to 10°C in a few hours on a hot summer’s day and cool by the
same amount at night. The temperature of most streams is lowest in the upland and becomes gradually warmer in the
lower reaches.
The velocity of stream water varies with the landforms. In plains, streams are slow and sluggish throughout their length.
In mountain stretches the speed of water may be rapid.
Stream water has uniform temperature and the difference between the surface and bottom is virtually negligible. The
stream follows air temperatures more closely than lake waters and the factors responsible are depth of water,current
velocity, bottom material, temperature of entering water,exposure to direct sunlight and degree of shading etc.
Extreme of turbidity occur in running water series and streams with rock beds the turbidity is minimal.
Stream systems increase their length, width and depth with increasing age. This is in distinct contrast to the reduction
processes characteristic of all standing water units.
At any position along the course of a running water system, materials eroded at that point and all materials suspended or
dissolved at the level are transported downstream with no opportunity to return. Interchanges of materials are more and
have less depth than lakes.
Chemical conditions
The dissolved oxygen supply in uncontaminated stream is high at all levels often near saturation. The polluted streams
show low dissolved oxygen due to accumulation of organic wastes. Stream which support more plants show diurnal
variation of dissolved oxygen. The level of dissolved oxygen is controlled by the slope of channel and mode of flow.
Current in streams tends to keep the pH in uniform over considerable distances. It keeps any acidity due to accumulating
free CO2 reduced. Streams waters do not develop the more intense acidities.
The dissolved solids of streams are affected by their irregular discharges. Most streams and rivers have maximum
discharge during winter rains, particulate matters, nutrients like phosphate, iron and nitrate are transported to different
parts by the flow of the streams. Streams fed by springs have more constant nutrients.
B. RIVER
River is said to be a natural stream of water usually fresh water flowing towards an ocean. In some cases river flows into
the ground or dries up completely before reaching another body of water. Usually larger streams are called rivers while
smaller streams are called creeks,brooks, rivulets, rills, and many other terms.
A river is a component of the hydrological cycle. The water within a river is generally collected from precipitation,
through surface run off, ground water recharge and release of stored water in natural reservoirs such as glacier.
Topography
The water in a river is usually confined to a channel, made up of stream bed between banks. In larger rivers there is also
a wider floodplain shaped by flood waters over-topping the channel. Flood plains may be very wide in relation to the
length of river channel. This distinction between river channel and floodplain can be indistinct especially in urban areas
where the floodplain of a river channel can become greatly developed by housing and industry.
Ecology
The flora and fauna of rivers use the aquatic habitats available, from torrential waterfalls through to lowland mires
although many organisms are restricted to the freshwaters in rivers eg salmon and Hilsa.
Flooding

8
Flooding is a natural part of river cycle. The majority of the erosion of the river channels and the erosion and deposition
on the associated flood plain occur during flood stage. Human activity, however has upset the natural way flooding
occurs by walling of rivers set straight their courses and by draining of natural wetland.
Lakes
2.1.1 Lakes
Lakes origin
Lake is defined as a large body of standing water occupying a basin which does not have any connection with
sea. Approximately 1% of water is found in lakes, but the renewal time is much more rapid than the ocean.
Classification of lakes on the basis of their origin
1.Tectonic lakes
These are formed in basins created by movements of the earth’s crust by different processes.
2.Crater lakes (Volcanic lakes)
In many cases when a volcano becomes extinct, its hollow interior is filled with water by precipitation or by percolation.
They are near circular or sometimes elliptical in outline. eg, Crater lake in Oregon (USA).
3.Glacial lakes
Most common lakes are originated due to erosion and deposition associated with glacial ice movements eg. Finger lakes
of New York.
4.Basal rock dissolution lake
These are formed by the slow dissolving of soluble rock (Calcium carbonate) by water eg,clear lake in California and
Deep lake Florida (USA).
5.Oxbowlakes
An oxbow is a crescent-shaped lake lying alongside of meandering streams or rivers in the floor of a valley. The oxbow
lake is created over time as erosion and deposits of soil change the river's course. On the inside of the loop, the river
travels more slowly leading to deposition of silt. Water on the outside edges tends to flow faster,which erodes the banks
making the meander even wider. When the streams bend and are cut off from the main stream flow, an oxbow lake
results. Such lakes may be entirely cut off and become totally lentic or a little flow may persist seasonally at floods. eg,
Dal and Woolar lakes of Kashmir.
6.Fluvial lakes
These lakes are formed by river activity.
7.Aeolian lakes
These are formed by the wind activity in arid regions which may erode with broken rocks or redistribute sand which are
generally temporary.
8.Shoreline lakes
Created by irregularities or inundation along the coastline of large lakes which usually a result of long shore currents.
9.Reservoir lakes
These are man made lakes formed by the construction of dams across the streams eg, Thungabhadra reservoir in South
India, Bhakra-Nangal reservoir in north western part of India (Anthropogenic lakes).
10.Bog lakes
Bogs are best developed in the north temperate glaciated region when precipitation is abundant throughout the year,
atmospheric humidity is great. Soil temperature is low, evaporation is reduced, and run-off water is minimum having
abundant growth of plants. A typical bog lake is defined as an area of open water surrounded either wholly or by part of
true margins. Possessing peat deposits about the margins or in the bottom usually with a false bottom of very finely
divided flocculent vegetable matter.

9
11.Salt lakes
There are many salt lakes throughout the world, much as saline lake waters as freshwater lakes. When climate change
become drier or geological events change drainage basins, the annual flows into lake may be greatly reduced. The lake
may seem to have a significant outflow and become a terminal or sink lake. The salts from the flowing stream are
concentrated by evaporation and are no longer flushed out through outflow eventually the lake may dry completely. In
dry climates the lakes gradually become salty.
Lake Bonneville and Lahontau of south western United States, the Great Salt Lake, Utah and lake Walker and Pyramid
in Wiveda are other examples. Salt lakes also found in areas of drier climates such as Australia, South America, East
Africa, Antarctica,Russia and dry northern side of Himalayas, South and North East America.
2.1.2 Thermal Classification oflakes
According to Hutchinson (1957), following are the classification of lakes based on changes in temperature of surface
water.
a. Amictic: No mixing of bottom and top water; lakes insulated or protected by ice-corer,there is no effect of weather
or external factors.
b. Monomictic: One mixing of the two waters during the year (most deep lakes of the world).
c. Cold monomictic: Water here at any depth never exceeds 4°C; they are ice-bound or ice-covered only in winter;
there are inverse thermal stratification top waters 0°C and bottom waters 4°C (since water at 4°C is heaviest); only one
mixing at temperatures not more than 4°C in spring / summer eg, Polar lakes.
d. Warm monomictic: Temperature of water never falls below 4°C at any depth. Direct thermal stratification top
waters 10 - 20°C and bottom waters 8 - 4°C; only one mixing in a year in a winter eg, Most subtropical deep lakes.
e. Ploymictic : Mixing is continuous, but occurs only at low temperatures.
Size of lake
Lakes differ in area from those ranges from a pond to those of great size. Lake Superior, the largest body of freshwater
flow has an area of more than 49,600 km2
. The Caspian sea with an area of 2,72,000 km2
is sometimes considered as
having the quality of lake.
Lake Chad in Africa has 64,000 km2
during wet season,but is reduced to 9,600 km2
in the dry season. Ten of the large
lakes in America including Great lakes have an combined area of about 2,03,200 km2
. However the number of lakes
whose area exceeds more than 8,000 km2
is insignificant when compared to many thousands of lakes of lesser
magnitude of 11,000 or more lakes or ponds in Michigan.
Depth oflake
Lakes vary in depth but even the deepest lake will never approaches the depth of ocean. It is important to note that the
lake Baikal has a greatest depth contains about 20% of the total volume of freshwater and it is also the deepest known
lake with a maximum depth of 1620 m. In North America, Crater lake in Oregon is about 608m. Lake Tahoe is 487m,
Lake Chelan (Washington) 457m. Seneka lake 188m, Lake Superior 393m, Lake Michigan 281m, Lake Huron 228m,
Lake Ontario 273m, Lake Erie 64m, and the last 5 lakes constitute Great lakes of America.
Lake margin
Nature of margin
The line of demarcation between land and water is the margin of the lake which depends upon a number of
circumstances.
Shore dynamics
Water is in some form of motion ranging from gentle to violent. It has a great potentiality to cause changes on the shore
against which it beats. In lake, the wave action is the principle form of water movement that cause shore changes.
Modification of the original shore line has been accomplished by two main phenomenon such as shore cutting and shore
building.
Lake bottom
The term lake bottom includes all part of bottom of lake basin from the water edge to the deepest region. All lakes of
particular region may have the same origin, may have begun the history with same material and exist at the same
climatic condition, yet the bottom material may often be different in different lakes. The kind of bottom deposits and the

10
rate of deposition may depend upon the local circumstances. The nature of bottom deposits determines the biological
productivity. The principle sources of bottom materials are
i. Bodies of plankton organisms which die and sink.
ii. Plant and animal remains.
iii. Organic and inorganic materials.
iv. Silt, clay and similar materials.
v. Marl or CaCO3 precipitated produced by plants and animals.
vi. Remains of floating blanket algae.
Diversity oflake
Though all the lakes appear to be similar, there may be differences in colour, taste,hardness, turbidity and aquatic
animals and plants. With the knowledge and the modern methods of environmental analyses, the lakes posses physical,
chemical and biological diversity. According to a great diversity, lake may be stated into different forms as under :
a. Large,medium or small.
b. Deep or shallow.
c. Protected or unprotected.
d. With or without tributaries and outlets.
e. Fresh, brackish or salt.
f. Turbid or clear.
g. Acid, natural or alkaline
h. Hard,medium or soft.
i. Surrounded by bog, swamp, forest or open shores.
j. High or low in dissolved content.
k. With or without stagnation zones.
l. With mud, muck or mucky sand or false bottom.
m. With high, medium / low biological productivity.
n. With / without vegetation beds.
o. Young, mature and senescent.
2.2.1. Famous lakes
Indian lakes
Almost every region of the country is dwelt by several of lakes that add great charm to their natural characteristics.
Rajasthan and Himachal Pradesh,North-Western state and Northern state of India, respectively are undoubtedly in
possession of larger number of lakes than anywhere else in the country.
Dal lake-Jammu-Kashmir
Dal Lake is a lake in Srinagar in Jammu and Kashmir. The urban lake, which is the second largest in the state,is integral
to tourism and recreation in Kashmir and is nicknamed the "Jewel in the crown of Kashmir" or "Srinagar's Jewel". The
lake is also an important source for commercial operations in fishing and water plant harvesting.
Location : Srinagar, Jammu and Kashmir
Lake type : Warm monomictic
Surface area:18–22 square km
Average depth : 1.42 m (4.7 ft)
Catchment area : 316 square km (122 sq mi)

11
Max. length : 7.44 km (4.62 mi)
Max. width : 3.5 km (2.2 mi)
Hebbal Lake- Karnataka
Hebbal Lake is located in the north of Bangalore at the mouth of National Highway 7, along the junction of Bellary road
and the outer ring road. It was one of the three lakes created in 1537 by Kempe Gowda. Like most lakes or "tanks" in
the Bangalore region it was formed by the damming natural valley systems by the construction of bunds. The spread of
the lake in a study in 2000 was found to be 75 ha with plans for extending it to make up 143 ha. The catchment area of
the lake was found to be 3750 ha. In 1974 the lake area was 77.95 ha and in 1998 it was 57.75 ha. Based on the rainfall
of the region, the annual catchment was estimated at 15.2 million cubic metres with 3.04 million cubic metres during the
Northeast Monsoon, 10.12 million cubic metres during the Southwest Monsoon and 3.28 million cubic metres in the dry
season. The storage capacity of the lake was estimated in 2000 to be 2.38 million cubic metres with desilting raising it to
4.07 million cubic metres. Sewage inflow into the lake has altered the chemistry and biology of the lake.
Powai Lake-Maharasthra
PowaiLake is an artificial lake, situated in the northern suburb of Mumbai, in the Powaivalley located downstream of
the Vihar Lake on the Mithi River. The city suburb called Powai, shares its name with the lake. Population around the
lake has substantially increased over the years.
When it was built, the lake had a water spread area of about 2.1 square kilometres (520 acres) and the depth varied from
about 3 metres (9.8 ft) (at the periphery) to 12 metres (39 ft) at its deepest. The PowaiLake has gone through many
stages of water quality degradation. The lake water which used to supply to Mumbai for drinking water has been
declared unfit to drink. The Lake still remains a tourist attraction.
Location : Mumbai
Catchment area : 6.61 km2
Max. depth :12 m
Surface elevation : 58.5 m (191.93 ft)
Settlements : Powai
Loktak lake-Manipur
Loktak Lake, the largest freshwater lake in northeastern India, also called the only Floating lake in the world due to the
floating phumdis (heterogeneous mass of vegetation, soil, and organic matters at various stages of decomposition) on it,
is located near Moirang in Manipur state,India. The etymology of Loktak is lok = "stream" and tak = "the end". This
ancient lake plays an important role in the economy of Manipur. It serves as a source of water for hydropower
generation, irrigation and drinking water supply. The lake is also a source of livelihood for the rural fisherman who lives
in the surrounding areas and on phumdis, also known as “phumshongs. Considering the ecological status and its
biodiversity values, the lake was initially designated as a wetland of international importance under the Ramsar
Convention on March 23, 1990.
Location : Manipur
Lake type : Fresh water (lentic)
Primary inflows : Manipur river and many small rivulets
Primary outflows : Through barrage for hydropower generation, irrigation, and water supply
Catchment area : 980 km2
(380 sq m)
Chilka Lake - Orrisa
Chilka (Chilika) lake is a brackish water lagoon, spread over the Puri, Khurda and Ganjam districts of Orissa state on
the east coast of India, at the mouth of the Daya River, flowing into the Bay of Bengal. It is the largest coastal lagoon in
India and the second largest lagoon in the World. It is the largest wintering ground for migratory birds on the Indian
sub-continent. The lake is home to a number of threatened species of plants and animals. The lake is an ecosystem with
large fishery resources. It sustains more than 150,000 fisher–folk living in 132 villages on the shore and islands.
Microalgae, marine seaweeds,sea grasses,fishes and crabs also flourish in the brackish water of the Chilika Lagoon.
Lake type : Brackish
Primary inflows : 35 streams including the Bhargavi, Daya,Makra, Malaguni and Nuna rivers

12
Primary outflows : Bay of Bengal
Catchment area : 3,560 km2
Hussian Sagar - Andhra Pradesh
Hussain Sagar (Hyderabad, India) was built by Hazrat Hussain Shah Wali in 1562, during the rule of Ibrahim Quli Qutb
Shah. It was a lake of 24 square kilo metres built on a tributary of the River Musi to meet the water and irrigation needs
of the city. There is a large monolithic statue of the Gautam Buddha in the middle of the lake which was erected in
1992.
Location: Hyderabad
Lake type: artificial lake
Max. depth: 32 ft
Surface elevation: 1,759 ft
Brahma Sarovar - Haryana
Brahma Sarovar is a water tank sacred to the Dharmic religions in Thanesar,in the state of Haryana in North India.
Dharmic religions lay emphasis on taking bath for internal and external purity.
Max. width : 1,800 ft (550 m)
Surface area :1,400 ft (430 m)
Vembanad Lake - Kerala
Vembanad Lake (Vembanad Kayal or Vembanad Kol) is India's longest lake, and is the largest lake in the state of
Kerala. It is also one of the largest lakes in India.
Max. length : 96.5 km
Max. width : 14 km
Surface area :1512 km2
Max. depth :12 m
Upper Lake - Madhya Pradesh
Upper Lake, is the largest artificial lake in Asia which lies on the Western side of the capital city of Madhya Pradesh,
Bhopal. It is a major source of drinkable water for the residents of the city, serving around 40% of the residents with
nearly 30 million gallons per day.
Location : Madhya Pradesh,Bhopal
Primary inflows : Kolans River
Catchment area : 361 km²
Surface area :31 km²
Kodaikanal Lake - Tamil Nadu
Kodaikanal Lake, also known as Kodai Lake is a manmade lake located in the Kodaikanal city in Dindigul district in
Tamil Nadu, India. The lake is said to be Kodaikanal's most popular geographic landmark and tourist attraction. Over
the years a boat club, boathouse and boat service for the public and tourists has become fully functional and is of
aesthetic significance for tourism. Boat Pageant and Flower Shows is a regular feature in the summer season which
attracts tourists.
Location : Kodaikanal, Dindigul district, Tamil Nadu
Lake type : Fresh water
Surface area :24 ha (60 acres)
Average depth : 3 m (9.7 ft)
Pushkar Lake- Rajasthan
Pushkar is an artificial lake located in the state of Rajasthan in India. It is situated near the Pushkar town in the district
of Ajmer. The lake was constructed in the 12th century with the establishment of the dam across the headwaters of the
Luni river. The pious Pushkar Lake is regarded as the sacred lake among the Hindus in India.
Osman Sagar Lake
Popularly known as the 'Gandipet', Osman Sagar Lake is the man made lake created by the dam across the Isa,a
tributary of the river Musi. It is the main source of water supply to the twin cities of Hyderabad and Secunderabad.

13
Bhimtal Lake
Located 22 km from Nainital, and this lake is named after the second Pandava called Bhima of the famous epic
Mahabharata. It is one of the largest lakes in the Nainital and the second largest lake in Kumaoun. The lake provides the
excellent opportunity for boating, fishing and angling.
Roopkund Lake
Roopkund Lake lies in the Chamoli district of Uttranchal at the height of 5029 meter. The lake provides the stunning
view of the Trishul peak (7122 meter) and due to its less depth it also known as the shallow lake.
2.3.1. Lakes ofthe world
Largest by continent
The largest lakes (surface area) by continent are:
• Australia - Lake Eyre (salt lake)
• Africa - Lake Victoria,also the third-largest freshwater lake on Earth. It is one of the Great Lakes of Africa.
• Antarctica - Lake Vostok (sub-glacial)
• Asia - Lake Baikal (if the Caspian Sea is considered a lake, it is the largest in Eurasia, but is divided between the two
geographic continents)
• Oceania - Lake Eyre when filled; the largest permanent (and freshwater) lake in Oceania is Lake Taupo.
• Europe - Lake Ladoga,followed by Lake Onega,both located in northwestern Russia.
• North America - Lake Michigan-Huron,which is hydrologically a single lake. However,lakes Huron and Michigan
are often considered separate lakes,in which case Lake Superior would be the largest.
• South America - Lake Titicaca, which is also the highest navigable body of water on Earth at 3,821 m above sea
level. The much larger Lake Maracaibo is considered by some to be the second-oldest lake on Earth, but since it lies at
sea level and nowadays is a contiguous body of water with the sea,others consider that it has turned into a bay.
Notable lakes
• Lake Michigan-Huron is the largest lake by surface area 117,350 km². It also has the longest lake coastline in the
world: 8,790 km. Compared to Huron and Michigan lakes, the Lake Superior alone comprises of 82,414 km². However,
Huron still has the longest coastline of 6,157 km.
• The world's smallest geological ocean, the Caspian Sea having a surface area of 394,299 km² which is greater than the
six largest freshwater lakes combined, and it's frequently cited as the world's largest lake.
• The deepest lake is Lake Baikal in Siberia, with a depth of 1,637 m and the mean depth is also the greatest in the
world (749 m). It is also the world's largest lake by volume (23,600 km³, though smaller than the Caspian Sea at 78,200
km³), and the second longest (about 630 km from tip to tip).
• The longest lake is Lake Tanganyika,with a length of about 660 km (measured along the lake's center line). It is also
the second largest by volume and second deepest (1,470 m) in the world, after lake Baikal.
Note : The world's oldest lake is Lake Baikal, followed by Lake Tanganyika (Tanzania).
• The world's highest lake is the Crater lake ofOjos del Salado,located at 6,390 m (20,965 ft). The Lhagba pool in
Tibet at 6,368 m (20,892 ft) comes second.
• The highest large freshwater lake in the world is lake Manasarovar in Tibet an autonomous region of China.
• The world's highest commercially navigable lake is Lake Titicaca in Peru and Bolivia located at 3,812 m (12,507 ft)
above sea level. It is also the largest freshwater (and second largest overall) lake in South America.
• The world's lowest lake is the Dead Sea,bordering Israeland Jordan located at 418 m (1,371 ft) below sea level. It is
also one of the lakes with highest salt concentration.
• Lake Huron has the longest lake coastline in the world of about 2980 km, excluding the coastline of its many inner
islands.
• The largest island in a freshwater lake is Manitoulin Island in Lake Huron,with a surface area of 2,766 km².
3.1.1. Nature ofInland water environment
Nature of lake environment
Lake basins with steep incline of bottom at the shore regions have margins which are less subject to changes. In lakes
with bordering low-lying swamp, bog or marsh areas,the margin shifts with elevation.
High and low water marks

14
The high water marks can usually be identified by ridges of debris and of certain bottom materials. Low water marks are
easily recognized from the positions of the more prominent animal an plant zones of shallow waters.
Shore dynamics
Water is restless and during calm period some form of motion varies from relatively gentle to violent. The inland lakes
the principal form of water movement produces shore changes. In lakes, particularly those of glacial origin, the shore
line is much regular and simplified. The modification of original shore line has been accompanied by two main
processes viz, shore cutting and shore building.
The shore cutting take place by the force of waves when the crest of oncoming wave is more or less to the shore line and
the final plunge of a wave lashes against the opposing land loosening a certain amount of it. If the shore is composed of
glacial drift or of soft materials, it will yield to continuously bombarding of waves. However,in regions of rocky areas
the shore cutting is slowed down but the erosion is facilitated by rock fragments which are picked by the waves.
On the other hand the shore building results from severalprocesses producing additions to the original lake margins.
Exposed sandy beaches form a beach building during summer by way of waves coming on to the gently sloping where
depth is less than the wave depth and thereby pushing and carrying ahead some of the sand. Under favorable conditions,
the end result is substantially increased breadth of beach (above water level).
Morphometry
It can be defined as the study that deals with measurement of significant morphological features of the basin of a body
of water and its included water mass is known as morphometry. Many fundamental ecological relations are directly
dependent upon structural relations of water it is necessary to make measurements of various morphological features.
Following general and morphometric information should be generated before studying structural and functional
attributes of the system.
Before taking up the morphological studies of a lake, general information regarding type, historical background,
location and general physiography should be collected.
• Type : The type of body of water viz, lake, pond, marsh, swamp, well, spring, stream,river, estuary, should be noted.
• Location : The locality, latitude, longitude and altitude at which the study area is situated should be noted from
authentic maps.
• Historical background :Collect the information pertaining to geological history of the basin and surroundings of
natural waters. For artificial bodies the construction or excavation details are of importance.
• General physiography : Salient physiographical features related to basin, bank and catchment area of the body of
water should be noted. This includes the features of bed-rock, coarse gravel, fine gravel, debris, mud, marl, peat, sand,
silt, clay, marshy, swampy etc.
The following morphometric parameters are of great importance.
1. Area:The surface area of water-spread can be calculated from a shore – line map of the body of water.
2. Bathymetry:A bathymetric or contour map is one which denotes the depth at different points in the body of water.
3. Maximum length:It is the length of line connecting two most remote extremities of the body of the water.
4. Maximum effective length:It is the length of line connecting two most remote extremities of the body of water
along which wind and wave actions occur without any kind of interruption. Maximum length and maximum effective
length may be the same in most cases.
5. Maximum width: It is the length of straight line connecting most remote transverse extremities of a body of water.
6. Maximum effective width:It is the length of straight line connecting more remote transverse extremities of a body
of water along which wind and wave actions occur without any kind of land interruption.
7. Mean width or Mean breadth ( b ) : It is equal to the area divided by maximum length ( b ) = a/l
8. Depth:It is the vertical distance between the surface and the underlying bottom.
9. Maximum depth:It is the depth measured at the deepest point.
10. Mean depth:It is calculated by dividing the volume of the body of water by its surface area
( z ) = v/a = Volume / area.
11. Outline map: Representing the outline structure of a lake in a plane surface is called outline map.
12. Topographical map: Representing various layers of lake basin on a flat surface is called topographical map.
13. Bathymetric map: Map representing the structure and lake basin is called bathymetric map. This can be derived
from outline map and topographical map.
14. Relative depth (Zr):It is the ratio of maximum depth in meters to the square root of area in hectares. Zr = a2 in
hadm /

15
15. Shore line:Shore line may be measured on a map by using an instrument called rotometer.
Area of the surface and each depth contour is measured by a digitizer or a polar planimeter.
3.2.1. Physical Characteristics
Pressure
Water is a heavy substance. Pure water weighs 62.4 lb (pounds) per cubic feet at 4°C. This is a direct result of
density. Since, density changes with differences in temperature, compression, substances in solution and
substances in suspension; the weight of a cubic foot of natural water is not always the same. The pressure at
any subsurface position is the weight of the superimposed column of water plus the atmospheric pressure at
the surface. As depth increases, the pressure in water is rapidly become great, so that ultimately a crushing
effect is imposed upon objects submerged to considerable depths. This collapse under pressure is called
implosion. The pressure change in lakes and reservoirs are very small than compared to sea. In lake, having
maximum depth of 100 ft., the pressure in the deepest region is about 58 lb. per sq. in. (4 atmospheres).
Compressibility
Water is virtually incompressible. The coefficient of compressibility for each atmosphere of pressure is
usually given as 52.5 x 10- 6 at 0°C for pressures of 1 to 25 atmospheres. Lake Superior waters, suddenly
rendered absolutely incompressible, would rise in level about 23 cm and an ordinary inland lake with the
maximum depth of 100 ft. under the same circumstances, would rise about 0.25 mm. Since, increasing
pressure compresses the water, thereby increasing its density to the same slight extent, objects sink in water of
uniform temperature at essentially the same rate at all levels.
Density
Some of the most remarkable phenomena in Limnology are dependent upon density relations in water. The
density of water depends on the quantity of dissolved substances, the temperature and the pressure. With
increasing amounts of dissolved solids the density increases in a roughly linear fashion. The quantity of
dissolved solids for inland waters is usually below 1 g / l, except, for mineral waters (springs) inland salt water
bodies, and water bodies subjected to marine influence. The density difference due to chemical factors is not
more than 0.85 g /l and the density differences occurring in different zones of the same water body are usually
an order of magnitude less than this.
i) Variations due to pressure
Water at the surface, subject to a pressure of only 1 atmosphere, is considered as having a density of unity
(1.0); at a pressure of 10 atmospheres, the density is about 1.0005; at 20 atmospheres, the density is about
1.001; and at 30 atmospheres, it is about 1.0015.
ii) Variations due to Temperature
Pure water forms ice at 0°C, and steam at 100°C, but there is change in the density of the liquid due to
temperature. Water possesses the unique quality of having its maximum density at 4°C and it becomes less
dense when the temperature decreases from 4°C to freezing point. Density of water will be less during
summer and it will be high during winter. Sea water becomes heavier at 0°C. The temperature of maximum
density of sea water is 0°C, where as for fresh water it is 4°C.
iii) Changes due to dissolved substances
The total amount of dissolved substances in freshwater is less than that in sea water. Such substances usually
increase the density of water, the amount of increase depending upon the concentration of dissolved materials
and their specific gravity. Evaporation increases the density by concentrating the dissolved materials and the
dilution reduces the density.
iv) Changes due to substances in suspension
All waters contain some suspended particulate matter. The quantity and quality of these substances vary
greatly in different waters and at different times. Silt and certain other materials are heavier than water and
thus increase its weight and other material may have a specific gravity similar to that of water and cause no

16
significant change in weight. Density currents and related phenomena may be caused by substances in
suspension.
3.3.1. Physical characteristics
Mobility (Viscosity)
Water is an exceedingly mobile liquid. Nevertheless, it has internal friction (viscosity). This viscosity varies
with the temperature. Water is distinctly more mobile at ordinary summer temperatures than that are just
before it freezes. The viscosity changes with temperature. The response of water to wind of fixed velocity
would differ with different temperature of the water. Pressure does not cause any significant change in
viscosity.
Buoyancy is the direct outcome of density and varies with the same factors. The law of Archimedes states that
the buoyancy of an object is equal to the weight of the water it displaces. The greater the density, the greater
the buoyant force; the denser the water, the floating object will ride higher in the water. Thus, ship passing
from fresh water into sea water rises little higher, and the same ship with the same load would ride somewhat
higher in winter than in summer.
Movement of water
The principal forms of movements of water are waves, currents and seiches.
a) Waves
Waves are mainly produced by wind. They occur on every body of water in forms and magnitudes depending
upon various local conditions, such as area of open water; direction, and velocity of winds; shape of shore line
and relative amounts of deep and shallow water. The greater the expanse of water over which the wind blows
the greater the potential wave height, wave length, and wave velocity. Stevenson (1934) formulated a formula
for computing the maximum height of wave in small bodies of water as
h = 1/3 √F
h = Maximum height in water
F = Fetch of the wind in km.
In open water two types of waves are formed namely waves of oscillation and waves of translation.
 i.Waves of oscillation: In this type of wave, the water particle moves up and down but no horizontal
movement of water.
 ii.Waves of Translation: In this type of wave there is definite forward movement of water
Depth of wave action in water is of considerable limnological importance, but information about this is
lacking. It has been claimed that in the sea, wave action may exert an influence to a depth of 182 m.
b) Currents
Currents in lakes are mainly of three kinds, viz, vertical, horizontal and returning. True vertical currents
seldom occur in inland lakes, but may be present in large waters such as the Great Lakes. When present in
inland lakes, they are the result of some unusual thermal, morphological, or hydrostatic circumstance and
upwelling of water from deep water source.
Horizontal currents (undertow currents) are common in lakes. They are usually produced by wind and often
modified by the shape of shore line and form of the basin. The ratio of wind velocity to water movement
diminishes as the wind velocity increases. Also, water velocity diminishes with the increase in depth.
Returning currents are formed when water is piled up on an exposed shore as a result of an onshore wind.
Such action raises the water level at the position, and, as a result, the excess water may return underneath
along the bottom. The magnitude and duration of such currents depend upon the velocity and duration of the
wind. Steady vigorous, onshore winds may set up return currents which extend to the opposite side of the lake.
c) Tides
In inland lakes, tides are almost imperceptible, even in the Great lakes. Lake Michigan is said to have a tide of
about 5 cm. This virtually means that tides in freshwaters are so far as known is negligible phenomena in
Limnology.
d) Seiches
In lakes and along the sea coasts, oscillations of the water level occur under certain circumstances which are

17
called seiches (pronounced as Saches). A seiche consists of a local, periodic rise and fall of the water level. It
is an example of standing wave in which the water particles do not travel in circular orbits but the advance and
return of the particle are in the same path. Any influence which produces a temporary, local depression or
elevation of water level may produce a seiche.
3.3.2.Seiches
Most commonly produced seiches in lakes are due to :
1. Winds, temporarily strong, which pile up water on the exposed margin of the lake
2. Sudden change in barometric pressure over a portion of the lake area
3. Earthquakes
4. Land slides
5. Sudden, very heavy rainfall at one end of lake.
The amplitude depending upon the dimensions of the lake and the intensity of the initial cause may vary from a fraction
of a centimeter in small lakes to 1 m or more in large ones. In lake Geneva, Switzerland it is reported that the amplitude
of a seiche may reach about 2 m.
Forel (1895) used the following formula for computing the period of oscillation of a seiche in a lake whose basin has
definite regularity of bottom.
t = l/√gh
where,t = time of one half oscillation in sec
l = length of axis of seiches in meters
g = acceleration of gravity (9,809 m/sec2)
h = depth of water in meters
More complicated formulas were worked out for lakes having irregular basins. Whipple (1927) presents the following
formula.
t =2 l / 3,600√dg
where,t = time of oscillations in hours
l = length of lake (or length of axis of seiche) in feet
d = mean depth in feet along axis of seiche
g = acceleration of gravity (32.66 ft/sec2)
Seiche condition in lake Erie, the calculated period is 14.4 hr.
Forms ofSeiches
Forel (1895) showed that seiches are of different forms as follows
•Longitudinal seiches - whose axis corresponds with the direction of the long axis of the lake.
•Transverse seiches - whose axis lies in the direction of one of the shorter axes of the lake.
Both longitudinal and transverse seiches are of three different forms :
a) Uninodal - having one node
b) Binodal – having tow nodes
c) Dicrotic seiche – having two beats (show as two peaks on a limnograph) due to interference of unimodal and bimodal
seiches.
d) Plurinodal – having severalnodes
Lesser forms of water motion are sometimes called seiches as for example the short–period, back and forth flow of
water though narrow channels in certain localities in very large lakes and the subsurface seiches,a type which has been
postulated as the cause of certain submerged currents in lake Erie.
Subsurface waves,sometimes produced in large bodies of water,occur where subsurface water is denser than the
overlying water. A strong localized wind starts an impulse (wave) in the underlying layer of water which moves forward
in the direction of the wind. As this wave moves along the warmer lighter water just passes over the crest of the wave
but in the opposite direction, thus producing a surface current opposite to the direction of wind.
Subsurface seiches usually arise from a temporary displacement of the thermocline by the weight of piled up surface
water on one side of a lake due to strong wind action.

18
3.4.1. Physical characteristics- Surface film, Temperature
Surface film
When water is exposed to air, it acts as if it were encased within an extremely thin elastic, surface membrane. This
boundary is commonly known as the surface film and is interpreted as a manifestation of unbalanced molecular action.
However,at surface film, there is a surface tension due to unbalanced attractions between water molecules at surface on
one side only and upward attraction is lacking because there are no water molecules above them.
Surface tension is maximum in pure water than in any other liquid except mercury. Surface film provides support for
organisms and miscellaneous particulate material, upper as well as under surface of surface film offers mechanized
support.
Plants are pleuston whereas animals which are associated with the surface film are termed as neuston (minute and big).
Effects of surface film
a)Beneficial effects are (i) mechanical support and (ii) respiration mainly air breathing aquatic insects.
b)Harmful effects are (i) reduction of light penetration thereby it will have effects on photosynthesis and (ii) traps the
minute organisms thereby fall easy prey to big animals.
Temperature
Temperature is one of the most important factors in an aquatic environment. In fact,it is possible that no other single
factor has so many profound influences and so many direct and indirect effects.
Diurnal and seasonal variations are very much common in freshwater environments than in marine environment. A
diurnal variation range of 4.8 to 5°C has been recorded in a tropical pond with an average depth of 3.0 m. In shallow
water bodies within an average depth of 1.5 m, the lowest night temperature was 26.6°C. The highest day time
temperature was 32°C with a variation of 5.4°C. In flowing water bodies like streams and rivers there is no such wide
fluctuations in temperature.
Lentic waters of lakes and ponds undergo thermal stratification phenomenon according to seasons. Thermal
stratification has been reported most frequently in the lakes of tropical countries such as Java,Sumatra and India.
According to temperature relations lakes have been classified into three types
1)Tropical lakes : In which surface temperature are always above 4°C.
2)Temperate lakes : In which surface temperature vary above and below 4°C.
3)Polar lakes : In which surface temperature never goes above 4°C.
Decrease in temperature cause reduction in metabolism resulting in lower rate of food consumption. Extreme higher or
lower temperature has lethal effects on the aquatic organisms. Fluctuation in temperature of water regulates the breeding
periods, gonodal activation and thermal induced migration. On the basis of their ability to tolerate thermal variations,
most fresh water organisms are classified into stenotherm and eurytherm. Stenothermic are the organisms with a narrow
range of temperature tolerance while the eurythermic are those organisms with a wide range of temperature tolerance.
Source ofheat for evaporation
a)Sun
b)Water
c)Surroundings
Inland waters are subjected to very extreme variation of temperature due to small expanse and shallow areas and get
heated rapidly during day and are cooled at night.
Rate of evaporation is determined by severalfactors such as
a)Temperature
b)Relative amount of free surface area of the water
c)Vapour pressure
d)Barometric pressure
e)Amount of wind action
f)Quality of water ie. fresh or salt
e) Thermal conductivity
The thermal conductivity of water is very low. Heat coming to a lake from the sun as partially absorbed and to some
extent conducted, but the really effective heat distribution is due to wind action in agitating the water and to a much
more limited extent, to convection currents.
f) Convection
Convection is the process of the transfer of heat by the movement of heated particles themselves. For eg, when water in
a beaker is heated by a flame placed below it, that portion of water first heated, expand and rise while the upper, colder,

19
denser portion sink. If the heat supply continues for some time, there are thus set up ascending and descending currents
by means of which heat is carried all through the total water mass. This form of heat distribution is known as
convection. Most forms of artificial heating of water are of this type.
Convection does occur under the following conditions:
Cooling and sinking of surface water as when the sun sets and under conditions of falling air temperature
a) Entry of colder water from a tributary
b) Cooling of surface water with the passage of autumn into winter
c) Alterations of winds and calm conditions
d) Entry of cooler subterranean water at a high level in the basin
e) Advent of rain in temperate region
f) Cooling of the surface water by evaporation
All the plants and animals have an adaptation to certain range of temperature ie. - 200°C to the boiling point of +100°C.
Some can withstand very low temperature for a short duration in an active state and some blue green algae and bacteria
living in hot spring (mineral) condition exist at temperature up to 90°C, however they reproduce at a slightly lower
temperature.
3.4.2. a) Thermal stratification
In tropical lake, heat intake at the surface leads to the formation of a vertical temperature gradient, within
which the thermal resistance become too great for the existing winds to continue mixing the whole water
masses. The upper warmer layer is called epilimnion and the lower cooler layer is called hypolimnion. In
between the two distinct portions, a layer called thermocline.
Summer stratification
In summer, there are three distinct layers are called epilimnion (upper layer), a bottom layer called
hypolimnion and the middle layer called thermocline or metalimnion.
Epilimnion
a) It is upper layer of water.
b) It is warmer layer.
c) The temperature of this layer fluctuates with the temperature of the atmosphere. It will be about 27°C to
21°C.
Hypolimnion
a) It is the bottom layer of water.
b) At this layer, water will be cool.
c) The temp is between 5°C and 7°C.
d) It is a stagnant column of water.
Thermocline (metalimnion)
a) It is the middle layer.
b) The temperature is in between the temp of the upper layer and that of the lower layer.
c) It is characterized by a gradation of temperature from top to bottom.
d) It is also called transition zone.
In deeper lakes, a seasonal, thermal phenomenon occur which is so profound and so far reaching in its
influence that it forms, directly and indirectly the substructure upon which the whole biological framework
rests, particularly in the temperature zone. Therefore, a clear understanding of the salient features of thermal
stratification is a necessity.
Thermal relations during spring
Uniform temperature of 4°C prevails throughout the water column of the lake. Wind depresses water at
windward side and drives towards leeward side (towards the sheltered side), sinks at this end and moves at the
bottom. This results in through mixing which is known as isothermic or homothermic condition.
During summer

20
As spring advances warmer winds and sun’s radiation increases surface water temperature. Water expands
above 4°C and thus water at the surface is lighter than underlying colder water. Upper layers become more
warm and lighter and no mixing can takes place. Wind drives water towards leeward and it sinks at that side
which will sink down but not reaching the bottom of the lake but will be stopped at some intermediary level
above cooler (colder) bottom water (Hypolimnion).
Currents in the upper lake will induce a counter current which is of a lesser magnitude in the bottom lake. At
this depth, the current direction will be towards the opposite side of the lake ie, windward side from leeward
to wind ward, sinks at this end and returns as the counter current at this region of lake. Thus two distinct
layers are seen at this time in the lake. Between these two layers, temperature drops suddenly, upper layer in
contact with the warmer waters of upper lake which is mixing by warmer winds and conduction.
On the other hand, the lower layers of this region is in contact with the layer which is yet to gain heat through
conduction and other processes which are themselves slow process. This separating zone between upper lake
and bottom of lake is called as Thermocline region. It is defined as a region wherein the temperature drops by
more than 1°C per meter of depth. The term of thermocline was proposed by Birge (1897). Thus, epilimnion /
upper lake is above thermocline and bottom lake / hypolimnion is below region of thermocline.
During fall (autumn)
Cold wind blow over the lake surface which cools surface water which become denser at -4°C. These denser
waters sink through lighter warmer waters to a level where it meets the waters of similar density ie. first it will
be at thermocline. Thus epilimnion gradually cools and on the other hand the hypolimnion will maintain the
same temperature. A stage will be reached when there will be no thermocline region, water freely mixes. This
mixing is called fall overturn. Mixing continuous till the temperature throughout will be at 4°C.
During winter
Cooling below 4°C will make water lighter and thus the surface waters are lighter than the warmer but denser
subsurface water. This water floats and no sinking, cooling continuous at surface till ice is formed at 0°C.
Once ice is formed at the surface wind has no effect as far as mixing is concerned a period of stagnation sets
in.
During spring
With the onset of spring, warmer sun rays and wind melt the ice cover. Now colder but lighter water will be
above warmer but denser water below. Once it attains a temperature of 4°C, it sinks down and reaches a level
of 1°C which being lighter ascends up and in turn warms up. Thus the layer of denser water increases until the
whole lake is uniformly of a same temperature. Mixing takes place now by spring winds and this is called as
spring overturn.
3.5.1. Physical characteristics- Light, Colour, Turbidity
Light
Light influences freshwater ecosystems greatly. Fresh waters contain more of suspended materials. These
suspended materials obstruct the light that penetration reaches the water. The degree of such obstruction of
light influences the productivity of the freshwater ecosystem. A shallow lake receives light to its very bottom
resulting in an abundant growth of vegetation both phytoplankton and rooted vascular plants. Light affect the
orientation and changes in position of attached species and their nature of growth and it also causes the diurnal
migration of planktonic organisms. The factors affecting the light penetration in natural waters are the
intensity at the surface, angle of contact of light with surface, differences in latitude, seasonal differences,
diurnal differences and suspended materials.
The light intensity at which oxygen production by photosynthesis and oxygen consumption by the respiration
of the plants concerned are equal is known as the compensation point, and the depth at which the
compensation point occurs is called the compensation depth.
Light exerts a great influence on many biological process of water. Most important future of water is its
transparency. This fluctuates in different seasons and water bodies such as flooding livers, mountain streams
etc. The source of light on the earth - a) Sun and b) Moon
Electromagnetic spectrum emitted by Sun (a) short gama rays (0.0001 mm) to (b) long Hertizan waves
(several km long). The Hertizan waves are the electromagnetic waves used in radio and it is pronounced as
Hertz.

21
Intensity of light is the number of quanta passing through on a unit area, ie, light energy and the unit of
expression of light intensity is ‘Lux’
Wave length is the measure of light colour
nm = nanometer = mille micron 10-9
AO = 1/ton billionth of a meter
nm = 1/billionth of a meter or 10AO
Intense radiation is restricted to 300 to 1300 nm. Peak radiation distribution is in the blue green range.
Wave length heating water is 0.1 to 770 nm (infra red spectrum).
In a year the amount of radiant energy that reaches earth from the sun is 1.3x1021 k cal
Visible wave length/light : 400 to 770 nm; Ultraviolet light >286 to 400 nm
Light penetration in natural waters is affected by
a) Dissolved substances
b) Suspended substances
c) Planktonic organisms
d) Geographical features (latitude and longitude etc)
e) Meteorological conditions
f) Angle of light etc.
Methods for estimation
a) Secchi’s disc
Secchi (1865), an Italian professor employed a metallic disc for measuring the transparency of waters of
Mediterranean sea. It considered in lowering into the water a white metallic disc of 20 cm in diameter, on a
graduated rope, noting / recording the depth at which the disc disappeared then lifting the dosc and noting the
depth at which it reappeared. The average of these two readings was considered the limit of viability or Secchi
disc depth. This method was used subsequently by many investigators. Whipple modified this method by
dividing the disc into four quadrants and paintings them in such a way that two of the quadrants which were
directly opposite to each other, black and intervening ones white. He also increased the efficiency of the
method by viewing the disc, as it sank in the water through a water telescope held under the sun shade.
This method is not actual measure of light penetration, but instead merely a useful rough index of visibility
when used under standard conditions. They are (a) Clear sky (b) Sun above the head (preferably) (c) Shaded
or protected side of the boat (d)) Under a sun shade. This method has come into a wide use as a means of
comparing different waters.
Factors influencing the light penetration
1) Intensity of light at surface
This varies (a) degree of clarity of sky (b) presence of fog, dust, smoke etc and (c) time of the day/season of
the year.
2) Angle of contact with surface
Light in contact with surface part of it is reflected rest enters water and becomes refracted. Penetration
depends on angle of contact and maximum penetration when sun is at zenith.
3) Different in latitude
More remote the water mass is from equator, greater will be the departure of sun’s rays from vertical and
hence penetration varies.
4) Seasonal differences
Closely associated with latitude are the seasonal changes in the position of the sun. Only locations at or
between 23° 28i N and 23° 28i S (Tropic of cancer and Tropic of Capricorn) ever have a vertical sum. Beyond
this zone, north or south not only do locations have on regular sun but the angle changes progressively with
change of seasons.
5) Diurnal difference
Angle of light in contact with water is ever changing during day, reaches zenith at noon.

22
6) Dissolved materials
One of the important factors is absorbance of light which varies with chemical substances such as (a) chloride
of Ca and Mg affect light penetration ie. Diminishes, (b) Traces of NH3 proteins, nitrate, carbohydrates etc
reduces the light penetration with respect to ultraviolet rays.
7) Suspended materials
Silt, clay etc. are effectively screen light and also the penetrations of light reduce by phytoplankton and
zooplankton.
Penetration of light in pure water
When light penetrates or enters into pure water (a) certain portion of light is absorbed and (b) some of it is
scattered in the form of deflection in all directions.
Absorption is selective in which certain wave lengths are absorbed more quickly than others.
Penetration of light in natural waters
Every quantitative determination records were only in marine waters probably because of more clarity. Here
photographic plate method used by Forel (1865) in lake Geneva at about 200 m.
3.5.2. Physical characteristics- Colour and Turbidity
Colour
Pure water bodies appear nearly black as they absorb all light components of the spectrum. The lake water containing
suspended materials is seen blue in colour due to the scattering of light by water molecules. Naturalwaters differ greatly
in colour, depending upon the materials dissolved and suspended in it.
It is a common misconception that in large water bodies, such as the oceans,the water color is blue due to the reflections
from the sky on its surface. Reflection of light off the surface of water only contributes significantly when the water
surface is extremely still, ie, mirror like, and the angle of incidence is high, as water's reflectivity rapidly approaches
near total reflection under these circumstances. Some constituents of sea water can influence the shade of blue of the
ocean and hence it can look greener or bluer in different areas.
Scattering from suspended particles also plays an important role in the color of lakes and oceans. A few tens of meters
of water will absorb all light, so without scattering, all bodies of water would appear black. Because,most lakes and
oceans contain suspended living matter and mineral particles as coloured dissolved organic matter (CDOM) and thus the
light from above is reflected upwards. Scattering from suspended particles would normally give a white color, as with
snow, but because the light first passes through many meters and the scattered light appears blue. In extremely pure
water as is found in mountain lakes, where scattering from white coloured particles is missing, the scattering from water
molecules themselves also contributes a blue color.
Turbidity
Degree of opaqueness developed in water by means of suspended water is known as turbidity. Turbidity producing
substances may be divided into two groups.
i) Settling suspended matters – those substances which in motionless water,will settle to the bottom sooner or later.
ii)Non-settling suspended matters - Finely divided solids or those materials whose specific gravity is less than water
which are in permanent.
The settling of particulate materials is by no means at a uniform rate,particularly in deeper lake having considerable
difference in temperature between the surface and the bottom layers.
Effects ofmaterials in suspension
a)Light reduction: Favourable for animals but unfavourable for plants (photosynthesis)
b)Effects of temperature: Turbid waters are warmer than clear waters. Suspended particles absorb heat more rapidly
than water itself and then radiate the heat to the surrounding water,adding to the heat content of the water.
Chemical characteristics
4.1. Dissolvedgases – Oxygen, Carbon dioxide and other dissolved gases
Dissolvedgases
No naturally occurring body of water is free of dissolved gases. Their spatial and temporal distribution is
dependent on factors such as precipitation, inflow and outflow, physical factors like temperature, movement
of water and chemical factors such as solution processes, combination and precipitation of reactions, complex

23
formation etc.
Among the dissolved gases present in water, oxygen and carbon dioxide are direct indicators of biological
activity of water bodies. Gaseous nitrogen only enters the metabolic cycle of a few specific microorganisms.
Hydrogen sulphide and methane occur in small localized amounts due to bacterial activity under conditions of
low redox potential and are incorporated into the material budget of water bodies by certain bacteria.
The Liebig’s law of minimum states that the yield is dependent on whatever growth factor is at a minimum in
proportion to all the other similar factors.
Solubility of Gases in water
The solubility of gases in water decreases with increasing temperature and decrease of pressure. When a gas
comes in contact with water, it dissolves in it until a state of equilibrium is reached in which the solution and
the emission of the gas are balanced. Total solubility of gas is expressed by Henry’s law. The concentration of
a saturated solution of gas is proportional to the pressure at which the gas is supplied.
Condition affecting the solubility of gases in water
Solubility of gases differs widely even when their pressures are equal. It is therefore necessary to find out the
solubility constants.
Henry’s law is stated as :
C= K p
Where, C = Concentration of gas in solution
p = Partial pressure of gas
K= Constant of solubility
The following general conditions affect the solubility of a gas:
i. Rise in temperature reduces solubility
ii. Increasing concentration of dissolved salts diminishes solubility
iii. Rate of solubility is greater when the gases are dry than when they contain water vapour
iv. Rate of solubility is increased by wave action and other forms of surface water agitation
A. Oxygen
The main sources of dissolved oxygen in water are:
i) The atmosphere and
ii) By photosynthetic activity of aquatic plants
Atmospheric oxygen enters the aquatic system:
a) By direct diffusion at the surface and
b) Through various forms of surface water agitations such as wave action, waterfalls, and turbulences due to
obstructions.
Aquatic chlorophyll bearing plants release oxygen as a byproduct of photosynthesis, which gets distributed
into the different layers of lake water by movements. In most lakes the phytoplankton contributes the bulk of
the oxygen supply because of the huge amounts of chlorophyll of algae in the epilimnion zone. In shallow
waters like ponds and swamps the limnetic photoautotroph may be overshadowed by littoral macrophytes,
attached algae, and the benthic algal mats. In small rivulets and brooks the periphyton account for most of the
production of oxygen.
The main causes of decrease of oxygen in water are:
i. Respiration of animals and plants throughout the day and night and
ii. Decomposition of organic matter – Aerobic bacteria use up of the oxygen of water while decomposing
organic matter. Chemical oxidation of sediments also takes place. Purely chemical oxidation may also occur,
but most of the oxidative processes in aquatic habitats are probably mediated through bacterial action.
iii. Reduction due to other gases – A gas may be entirely removed from solution by bubbling another gas
through the water in which it is dissolved. In nature, gases like CO2, methane and hydrogen sulphide often
accumulate in large amounts and the excess amounts rise in the form of bubbles removing the dissolved
oxygen.

24
iv. By physical process – In summer days the heat warms up the epilimnion zone of the lake, which could
account for oxygen depletion of water. The combined effects of all or some of the above mentioned processes
may completely deplete oxygen content of the system.
Diel oxygen changes in freshwaters
The concentration of oxygen in an aquatic environment is a function of biological processes such as
photosynthesis and respiration and physical processes such as water movement and temperature. Diel
variations occur in both day and night hours. Estimates of diel production can be made in natural waters by
considering night as the dark bottle and day as the clear bottle. The increase in oxygen from dawn to dusk
reflects net primary productivity. The decrease from dusk until dawn represents half the diel respiration.
Adding the oxygen that disappeared at night to the day time gain gives a sum that is daily gross primary
productivity.
B. Carbon dioxide
i) Sources of carbon dioxide in freshwater
The atmospheric carbon dioxide mixes with the water when it comes in contact with the water surface, as it
possesses the highest solubility in water. As the partial pressure of carbon dioxide in air is low, the amount
which remains in solution in water at a given temperature is also low.
1. Rainwater and inflowing ground water
Rainwater is charged with 0.55 to 0.60 mg/I CO2 as it falls towards earth. Water trickling through organic soil
may become further charged with CO2.
2. Byproduct of Decomposing Organic Matter (DOM)
Carbon dioxide is added to the water as a byproduct of decomposing organic matter which is a common
phenomenon in natural waters. Large quantities of the gas are produced in this way. It is found that carbon
dioxide is the second largest decomposition product, constituting 3 to 30 per cent of the total gas evolved.
3. Respiration of Animals and Plants
Respiratory processes produce and release carbon dioxide into the water. The quantities so added are
governed by the magnitude of aquatic flora and fauna, the relative size of the individual organism and those
factors which determine the rate of respiration.
ii) Reduction of carbon dioxide in freshwaters
The principal processes which tend to reduce the carbon dioxide supply are;
1. Photosynthesis of aquatic plants
Consumption of free CO2 in photosynthesis depends upon amount of green plants which the water supports,
duration of effective day light, transparency of water and the time of year.
Marl forming organisms
The following groups of aquatic organisms are known to form marl (=Crumble : large deposits of calcium and
magnesium carbonate) in water bodies; aquatic flowering plants like Potamogeton, Ceratophyllum,
Nymphaea, Vallisneria; many blue-green algae like Rivularia, Lyngbya nana, Lyngbya martesiana,
Colacacia. Centrosphaeria facciolaea; many species of diatoms; mollusks which form calcareous shells;
insects like Diptera larvae; the cray fishes and lime-forming bacteria. All these organisms function in the
production of the insoluble carbonates which involves carbon dioxide, calcium and magnesium. Thus the
process of lime formation binds up carbon dioxide supplied from circulation and removes the available
calcium and magnesium from the system.
Agitation of water
Agitation is a very effective method of releasing free carbon dioxide from water. It is evident from the fact
that sometimes when deeper layers of water has large amount of it, the surface water shows very little carbon
dioxide.
Evaporation
Evaporation of waters containing bicarbonates results in the loss of half-bound carbon dioxide and
precipitation of mono carbonate. The form of loss is greatest in shallow water bodies where evaporation is

25
most effective.
Rise of bubbles from depths
Free carbon dioxide often accumulates in decomposing bottom deposit in such quantities that at frequent
intervals increasing internal pressure of gas exceeds the external pressure and the excess gas rises in the form
of masses of bubbles to the surface and is lost into the air.
Other dissolved gases
i) Methane
Methane, sometimes called marsh gas, is one of the products of decomposing organic matter at the bottoms of
marshes, ponds, rice field and lakes. The methane bacteria are obligate anaerobes. They decompose organic
compounds with the production of methane (CH4) through reduction of either organic or carbonate carbon.
Conditions favorable for production of methane appear at about the time the dissolved oxygen content is
exhausted. This is because methane (CH4), a compound of carbon and hydrogen burns in oxygen forming
oxides of carbon and hydrogen ie, carbon dioxide and water.
It has been found that large quantities of methane are produced in marshes and eutrophicated lakes during
summer time.
ii) Hydrogen Sulphide
Hydrogen sulphide dissolves very rapidly in water and is thus not dissipated like methane. The bottom water
of stratified eutrophic lakes may contain appreciable quantities of the very soluble gas H2S. This is especially
marked in lakes of regions of high edaphic sulfate. The reduction of sulfate to sulfide is a phenomenon largely
associated with anaerobic sediments. H2S is poisonous to aerobic organisms because it inactivates the enzyme
cytochrome oxidase.
iii) Nitrogen
Nitrogen has a low solubility in water. It is such an inert gas that the quantities which occur in lake water are
not changed by the chemical and biological processes. The atmosphere usually supplies the greater amounts of
nitrogen found in water. The minimum amount occurs in winter, since it is more soluble in cool water.
iv) Ammonia
Ammonia occurs in small amounts in unmodified natural waters. It is exceedingly soluble, 1 volume of water
dissolving 1,300 volume of ammonia at 0° C. In lakes, it is the result of the decomposition of organic matter
at the bottom. In summer, free ammonia ordinarily increases with depth.
v) Sulphur dioxide
Traces of sulphur dioxide may occur in natural waters.
vi) Hydrogen
Liberation of hydrogen in the anaerobic decomposition of lake bottom deposits seems likely. But, the amount
so formed is small.
vii) Carbon Monoxide
Carbon monoxide may occur in the bottom of the hypolimnion in small amount.
4.2.. Dissolved Solids and Dissolved Organic Matter
All waters in nature contain dissolved solids .Water is the universal solvent dissolving more different materials than any
other liquid. Natural waters come in contact with soluble substances in many ways such as mere contact with its own
basin, erosion at shore line, wind blown materials, inflow of surface waters,inflow of seepage and other forms of
subterranean waters and decay of aquatic organisms. Rain water contains 30 to 40 ppm of dissolved solids.
Solubility of solids in water
Salts are composed of ions which in the solid form are held together by ionic forces. The strong ionization of the salts
leads to the formation of hydrates with water in which the water acts as a dipole to which the ions are attached. The
solubility of solid substances is strongly dependent on the pH and the redox potential in the water. It usually increases

26
with temperature and is largely independent of pressure. Most substances dissolve either in the molecular form or
dissociated into ions. Some important constituents such as humic acids, salicilic acid and ferric oxyhydrate are dispersed
in colloidal form.
Major ions in freshwaters
The major ion contents vary in different fresh waters due to five factors,which are climate, geography, topography,
biotic activity and time. These are not completely independent and they interact.
Carbonate is the principal anion in most fresh-waters. Generally carbonate occurs as bicarbonate ion with calcium in
water. Bicarbonate ion is customarily expressed as CO3 because evaporation of a known amount of calcium bicarbonate
solution leaves only the carbonate of calcium to be weighed. During evaporation, gaseous CO2 and water are lost, from
bicarbonate ions, converting them to a lesser weight of carbonate.
Alkalinity is usually a measure of carbonates. There are various compounds of carbonates with calcium, such as calcite
or aragonite which have the same chemical formula (CaCO3),but are crystallized differently. Aragonite precipitates
from thermal waters and is contained especially in the shells of freshwater mollusks. Magnetite, the carbonates of
magnesium (MgCO3) and dolomite, a double carbonate of calcium and magnesium, Ca Mg (CO3)2 are also relatively
common. Carbonates of barium (BaCO3) and strontium (SrCO3) also occur. CaCO3 is insoluble except in the presence
of acid. With carbonic acid, it becomes Ca (HCO3)2. Because of this, it seems reasonable to express alkalinity titrations
in terms of bicarbonate ions, but on the other hand, Ca(HCO3)2 is very unstable and when water is evaporated to
determine its contained dissolved salts, the bicarbonate of calcium is destroyed and only carbonate remains.
Dissolved inorganic solids
i) Nitrogen compounds
Nitrogen occurs in natural waters in the form of numerous compounds, in inorganic form as nitrate, nitrite and
ammonium and in organic form as intermediate stages of microbial protein decomposition. The most important
inorganic nitrogen compounds in water are nitrate and ammonia. Natural waters contain some ammonium salts.
Ammonium carbonate is probably the common form.
iii) Phosphorus compounds
Free phosphorus does not occur in nature, but in the form of phosphates it is abundant. Inorganic phosphorus
compounds usually occur in dissolved form only in small amounts in natural waters,often only as traces. Total
phosphorus in lake water includes two components. One is soluble phosphorus which is the phosphate form and another
one is organic phosphorus which is contained in plankton organisms and other organic matter in the water. As an
essential nutrient for primary producers, phosphorus thus acts more often than nitrogen as the growth limiting factor.
The natural inorganic phosphate content originate from atmospheric precipitation as well as from various phosphate
containing rocks especially apatite, which are flushed into the lake by tributary streams. In lakes and flowing waters
three phosphate fractions occur concurrently : soluble inorganic phosphate as orthophosphate (PO4) and polyphosphate,
soluble organic phosphate and particulate organic phosphate (organisms or detritus). These fractions make up to total
phosphate content. The losses of phosphorus occur throughout flowing water which removes both soluble and organic
form. It may also occur through removals of fish, mollusks, water plants and other organisms.
iii) Sulfur compounds
The inorganic sulfur compound occurring predominantly in natural waters is sulfate. In this form sulfur can be absorbed
by phytoplankters and other photo-autotrophs. Purely chemical processes involved in the sulfur budget of natural waters
are the oxidation of hydrogen sulfide to sulfur by molecular oxygen and also the formation of sulfides, especially iron
sulfide in the sediment. The sulfate ion, SO4 is usually second to carbonate as the principal anion is fresh waters,
although chloride sometimes surpasses it. Silica often outranks sulfate, but very little is ionized. Free or elemental sulfur
is inactive at ordinary temperature. This element can combine with both metals and non-metals to form many
compounds. Free sulfur is an important constituent of protoplasm; it is protein and specifically within those amino acids
having sulfhydryl (SH) bonding; e.g. cystine, cyseine and methionine.
When sulfur is combined with hydrogen the most reduced state is sulfide (S- -) and the most important sulfides in
limnology are the gas - hydrogen sulfide (H2S) and ferrous sulfide (FeS). Sulfates combine with hydrogen to form
sulfuric acid. With the alkali metals sulfur forms the most abundant form in lakes and streams.
Atmospheric sources of sulfate have increased with man’s industrial activities. Man now contributes about ten times
more SO2 than that the annual contribution from volcanoes. Coal combustion produces the gas maximum and copper
smelting and paper manufacturing add to it. Through precipitation and runoff water the sulfate level of some fresh water

27
becomes unusually high showing industrial water pollution.
The most important conversion process for sulfur in lakes can be summarized as follows: sulfate is reduced by the
desulphuricans to H2S and sulfides which are deposited in the sediment. Hydrogen sulfide is also formed by the
microbial decomposition of proteins which is oxidized by Thiobacteria, Chromatiaceae and Chlorobiaceae via molecular
sulfur to sulfate.
iv) Silicon
Silicon does not occur in nature as a free element. Natural waters commonly contain silicon dioxide in some form of
soluble silicate. Silica may also exist in certain waters,particularly in rivers, in colloidal form. River waters are
relatively rich in silica. Silica is the second most abundant element in the lithosphere. Its main source in fresh water and
sea water is weathering of the feldspar rocks. In inland waters it ranges from 0.1 ppm. Solubility of silica increases with
the rise in temperature. Dissolved silica remains as H2SiO4. Silica is an essential nutrient for diatoms as they build up
their frustules with this material. The decay of silica is slower than organic compounds and thus many diatoms frustules
may be buried and lost to the lake sediments.
Other Elements
Certain elements such as calcium, magnesium, manganese,iron, sodium, potassium, sulphur, copper and others
constitute elements of chemical compound dissolved in the water.
i) Calcium
The predominant compound of calcium is CaCO3,which is very less soluble in water but in the presence of carbonic
acid it is represented abundantly as the soluble Ca (HCO3)2. Thus there is an inseparable relationship between carbonic
acid, CO2, pH and the anion CO3-in water.
The earth’s crust contains an ample store of calcium as a constituent of certain silicates. Anorthite (CaAl2Si2O8) is a
common member of the feldspar group of silicates. They are the most abundant of all minerals and make up 60% of the
earth’s coating. A deposit of sedimentary CaCO3 is changed to soluble bicarbonate by the action of CO2 rich meteoric
water (rain water) which enters aquatic systems. The solubility of CaCO3 depends on CO2 which follow the reaction:
CaCO3 – Ca (HCO3)2.This equilibrium is disturbed when the water emerged and the pressure on it suddenly released
making the escape of CO2. Also removal of CO2 in photo-synthesis will disrupt the equilibrium. CO2 is assimilated in
photosynthesis and CaCO3 gets precipitated in the form of calcareous incrustations on plants and other submerged
objects.
Other Minerals of Calcium
After the silicate and carbonate minerals of calcium, the sulfates rank as its most abundant store. These are gypsum,
(CaSO4,2H2O) and anhydrite (CaSo4).
ii) Magnesium
Magnesium is usually the second most abundant cat ion in inland waters. Its source is both silicate and non-silicate
minerals of the earth’s crust. Foresterite (Mg2SiO9) in the following manner:
The magnesium carbonate is called magnetite and a double carbonate is dolomite, Ca Mg (CO3)2. Epsom salt (Mg
SO4.7H2O) is a soft and whitish sulfate of magnesium. It is 150 times more soluble than gypsum (CaSO4.2H2O). Epsom
salt occurs in mineral spring deposits and in salt sediments of certain lakes.
iii) Sodium
The monovalent alkali metal is very reactive and soluble. When leached from the rocks, its compounds tend to remain in
solution. For this reaction, it is at least the third most abundant metal in lakes and streams and sometimes it ranks first.
Among igneous rocks, the feldspars, alumino silicates of alkali and alkaline earth metals are the most abundant of all
minerals. The commonest water soluble mineral is halite or simply Na Cl. In arid tracts like Rajasthan where closed
basins hold concentrated waters,there are at least 3 types of sodium lakes:
i) Slatterns, having concentration of sea water with preponderance of Na Cl.
ii) Saline lakes having Na2SO4 in water and
iii) The soda lakes characterized by NaHCO3 and Na2CO3.
They have been termed as alkali water because of their high pH. These soda lakes are characterized in having luxuriant
growth of blue-green algae.
iv) Potassium
Potassium, a close relative of sodium is usually the fourth ranking cat ion in freshwater. In usualcases it may surpass
sodium in certain lakes. It is weathered from various feldspars that have the formula KAISi3O8 but does not remain in
solution. Potassium also tends to form plates of mica, which are insoluble and unavailable to aquatic ecosystems.

28
Because of this formation potassium becomes rarer in water than sodium. In plants, both extracellular and intracellular
fluids contain an excess of K+ over Na+. In animals extracellular Na+ often surpasses potassium. There is some
evidence that highly concentrated water with a pronounce potassium content are lethal to many aquatic animals, the
Na/K ratio being less than ten.
Potash is the name for K2CO3 but he word has been used to refer to KOH or potassium oxide. The so called potash lakes
occupy depressions among the sand in Nebraska in USA.
v) Iron and Manganese
Although iron is one of the most widely distributed elements on the earth, it occurs in natural waters only in relatively
small amounts due to its specific solubility properties. But the ground water contains large amounts of dissolved iron
and manganese. The compound of trivalent (ferric) iron is almost completely insoluble in water. Thus iron remains in
solution only in the bivalent form, under reducing conditions, and chiefly as the bicarbonate Fe (HCO3)2. The conditions
under which bivalent iron (ferrous) compounds remain in solution are:an oxygen saturation value of less than 50%, the
presence of degradable organic matter,a high level of free CO2 and a pH of less than 7.5. These conditions are found
primarily in groundwater and in the hypolimnion of lakes.
vi) Chloride
It is an element of the halogen group that includes also fluorine, iodine and bromine. Among these members, chloride
surpasses them in polluted as well as freshwater lakes and streams. Molecular chloride (Cl2) is a heavy yellow lethal
gas, but in natural waters,it is dissociated as chloride ions, which combine with all common cat ions. It is stored in most
freshwater algal cells. Contamination of water from domestic sewage can be monitored by chloride assays of the
concentrated water bodies. This is because a human and animal excretion contains an average of 5g Cl- per liter.
Dissolved Organic Matter
Freshwater contains 0.1 to 50 mg dissolved organic compounds (DOC) per litre. Various free sugars, amino acids,
organic acids, polypeptides and other substances have been reported.
There are probably four sources of these dissolved materials
1. Organic compounds of allochthonous origin
2. Soluble organic material from the decay of aquatic organisms
3. Extra cellular metabolites excreted by littoral macrophytes
4. Excretion from the fresh water animals.
The organic compounds not only serve directly as source of energy but also are associated with the nutrient cycle of the
ecosystem. Most metals are transported down streams or exist in lake making complexes with organic materials either
being absorbed or occurring as metallic coatings on detritus. Such organic substances as humic material causing yellow
stain in fresh water comes from the decay of plant material in the soil.
The origin of the dissolved organic compounds in the water is manifold. The losses are due to photorespiration,
secretion of the products of algal photosynthesis and those of higher plants and also due to the excretions of bacteria.
An important group of organic substances in water consists of humic substances. They are polymeric mixers derived
mostly from such plant materials as lignin. Cellulose, proteins and fats humic substances enter the water due to
incomplete breakdown of plant residues in the water bodies.
They affect the material budget in as much as they enter into complex-formation with heavy metals (iron and
manganese) and consequently prevent their precipitation and ensure their continued availability to the primary
producers. Thus a direct relationship may be observed between the concentrations of dissolved iron and water soluble
humic substances in lakes. Heavy-metal ions may also become adsorptive bound to particulate humic materials. This
tendency to chemical and adsorptive binding of heavy metals is of great importance for productivity in natural waters.
Calcium may precipitate as calcium humate on contact with humic acids and be deposited in the sediment.
Humic acids in sediments also form iron-humus-phosphate complexes and hence, phosphate combination with iron is
substantially reduced. The humic materials hold in suspension. The humic materials hold in suspension large quantities
of metallic ions and through their chelating activity hold on the essential trace metals are delayed in the presence of
humic compounds and thus hold the nutrients for a longer period in water.
Biological relations
5.1 Influence of physical and chemical conditions on living organisms in inland waters
Shoreline

29
The greater the length of the shore line the greater the biological productivity. Increased irregularity of shore
line results in
1) greater contact of water with land
2) increased areas of protected bays and covers
3) increased areas of shallow water for growths of rooted vegetation
4) greater diversification of bottom and margin conditions
5) reduction of the amount of exposed, wave-swept shoal and
6) increased opportunity for extensive, close superposition of the photosynthetic zone upon the decomposition
zone. These and other possible results combine in various ways to increase the production of animals and
plants.
Relation of photosynthetic and decomposition zones
The form of basin of a lake determines, among other things, the relative amounts of shallower waters. Within
limits and under strictly comparable conditions, the grater the areas of shallow water the greater the biological
productivity. Their exposed nature usually results in
a. the absence of rooted plants
b. the absence of organic bottom deposits and
c. the absence of any permanent animal population save those whose burrowing habits make occupancy of
position in such a habitat possible.
Nevertheless, a fairly substantial but largely concealed population may be present, although of all the shallow
water faunas it is usually the smallest one.
In contrast to conditions described above, the steeper the slope of the basin, or the greater the exposure of
shoals, or both, the greater the removal of the decomposition zone to the profundal depths of deeper lakes
A deeper lake with steep basin slope thus tends to automatically and continuously rob itself of its stores of
organic matter. Lakes of the third order, because of shallow depth and continuous circulation except during
the ice cover period, retain all organic accumulations in available position, the essential decomposition
products either remaining immediately beneath the plant beds or else being constantly the tribute by the water.
Slope and the deeper decomposition zone
Form of basin also involves the slope of deeper portions of the basin. Upon the nature of this slope depends, to
a large extent, the character of the bottom. The influence of gravity, aided by water movements in pulling to
the lowermost bottom the various materials which settle through, is much more effective on a declivitous
slope. Some basin slopes are so abrupt that very little of the loose, settling materials can remain on the steep
sides. Thus the decomposition zones of such a lake are restricted to (1) those of the shallow, protected shoals
(if any are presently), and (2) those at the bottoms of the deepest regions, separated by steep sides which
maintain little or no decomposition deposits.
5.2. Productive volume, flotation phenomena and body form adjustments
Productive volume
Form of basin determines the extent of productive volume. By productive volume is meant that portion of water in
which virtually all biological production occurs. In a lake of the third order, total volume is productive at least during
the open season. In lakes of the second order, productive volume is almost exclusively confined to the epilimnion and
the thermocline during most of the summer stagnation period. During the overturns, the entire lake temporarily becomes
productive volume but the duration of these periods may be too short to be or any great consequence. Lakes of the first
order resemble those of the second order in that they maintain the productive zone in the upper stratum, usually limited
by the presence of a thermocline. In those lakes having no complete overturn, the productive zone, during open season,
merely varies in volume with those conditions which determine the depth to which circulation may extend. During
prolonged ice cover, lakes of the second and third orders undergo gradual reduction of productive volume due to
encroachment of the underlying stagnation zone, while lakes of the first order, under these conditions, may undergo less
change in productive volume due to their size and to the presence of the permanent, deeper stagnation region. Complete
ice cover may not occur in lakes of unusual size and depth, even though located in colder regions.
Both depth and area of a lake basin combine in innumerable ways to produce a great heterogeneity of lake forms. Since

30
inland lakes seldom exceed certain area limit, depth is fundamentally of prime importance in determining productive
volume.
The average depth is the factor which determines whether a lake is eutrophic or oligotrophic, computing average depth
as the quotient of volume of the lake over area of the lake (V/A). In oligotrophic lakes, the volume of the hypolimnion is
greater than the volume of the epilimnion, and that in eutrophic lakes the reverse occurs.
Flotation phenomena
i). Non-motile organisms
In calm water,non-motile plankton organisms depend entirely upon the relation between their own specific gravity, the
density of the water,and the viscosity of the water in maintaining their vertical position. Non-motile, attached animals,
particularly the colonial forms such as the larger colonies of fresh-water sponges and certain fresh water Bryozoa
(Pectinatella), may develop forms and masses of body, which could not be maintained in the absence of the buoyant
effect of water,and even the soft bodied Hydra would be helpless without it.
All sessile animals depend, to some extent at least, upon the buoyancy of the water. Many higher aquatic plants are
dependent upon the supporting effect of the water in order to maintain their proper form and orientation.
ii) Motile Organisms
Those plankters which possess powers of locomotion vary greatly in the efficiency of their progression, but some
change of position in space is possible due to their own activity. While such locomotion may be almost negligible when
compared with the shifting and transporting effects of the water,it may nevertheless be vital to the organism in many
ways,such as in the capture of food, and in the change of water in contact with respiratory surfaces.
Locomotion in water,consumes less energy to maintain their position above the bottom, due to buoyant effect of water.
In fact,those organisms whose specific gravity is essentially the same as the surrounding water expend practically no
energy in merely keeping up in the water. Certain aquatic animals, because of the possession of air stores or other
special means, are distinctly lighter than water and must use a certain amount of energy to keep below the surface when
they need to do so.
Many air breathing, aquatic insects have air stores so located that not only are they lighter than water but the posterior
end is lighter than the anterior, enabling the insect to float at the surface in the proper respiratory position.
iii) Reduction of specific gravity
Protoplasm alone has a specific gravity which closely approaches that of water,but the various cell products which
occur in animals and plants may combine to produce bodies which are either heavier or lighter than water. Products
which tend to make the body heavier (such as chitinous exoskeletons of arthropods, bones, shells or various kinds) and
those which tend to make it lighter are often present in the same body so that the specific gravity of the whole depends
upon which of the contrasting materials predominate. The most effective and the most common of those cell products
which reduce specific gravity seem to be the following:
1.Gases originate from various sources (metabolic products, externaland internal air stores, and others) and remain, at
least for a time, enclosed within or attached to the body. These gas accumulations may be of sufficient magnitude to
make an otherwise heavy-bodied animal (as,for example, certain aquatic insects) much lighter than water.
2.Fats and oils are commonly produced and stored within aquatic organisms, notably in the plankton crustaceans and in
the plankton ie Algae.

31
3.Gelatinous and mucilaginous secretions of varying amounts are common as matrices and external envelopes which
helps in flotation.
iv) Relations of surface to volume
(a) In different Species.
Since in relatively compact bodies of organisms, the relations between volume and surface tend to conform roughly to
the well-known mathematical principle that the surface varies as the square of the dimension while the volume varies as
the cube of the dimension. The smaller the body, the greater will be the relative expanse of surface.
If the body has a specific gravity greater than water,it will sink, although resistance to sinking will be offered by the
viscosity of the water. The greater the surface compared to the volume the greater will be the friction between water and
body. Because of this relation, particles of very small size, even though composed of a substance having a specific
gravity greater than 1, may not sink at all.
Few aquatic organisms, irrespective of size, are spherical in form. Any departure from the spherical form results in
relatively increased body surface. Relative increase of surface is accomplished in so many different ways by :
1.General body form. Main portion of body may present:
a.Various degrees of attenuation.
b.Various degrees of compression or depression or generalflattening.
c. Miscellaneous forms of asymmetry.
2. Body surface sculpturing: ridges, furrows, striae, impressed or raised patterns.
3.Extensions and modifications of antennae, tentacles,gills, legs, cerciand others.
4.Development of special peripheral processes:hairs, setae,spines, bristles, filaments, radial axes, tubercles, cilia,
pseudopodia, crests.
5.Formation of colonies: linear, dendritic, radial, lamellate, irregular.
Combinations of severalof these structural features in the same organism may occur, sometimes with remarkable
flotation results.
(b) In the same species
In certain plankton organisms, a striking seasonalchange of body form of a very definite sort occurs. This change of
body form is a response to changes in the viscosity of the water due to seasonalchanges in temperatures.
(c) Accessory provisions of flotation
Cases and coverings of various kinds composed, of foreign materials are constructed by some aquatic organisms. While
such cases often serve severalother purposes. In certain cases that they either increase the tendency of the whole
organism to be in suspension or completely support it at the surface. Instances of this sort are not uncommon among the
aquatic insects (certain caddis-fly larvae, certain aquatic caterpillars, and others.
(d) Hydrofuge structures
Hydrofuge structures, such as hydrofuge pubescences,hydrofuge caudal filaments, and hydrofuge smooth surfaces,
often play an important and sometimes a vital part in the flotation of organisms. Once at the surface they may provide
(1) for the proper orientation of the body into the breathing position and (2) for the ability to remain at the surface in this
position without much effort during the breathing period. Examples are not uncommon among aquatic insects. Certain

32
hydrofuge structures are related directly or indirectly to respiration in some air-breathing aquatic insects.
(e) Precision in flotation adjustment
Among the plankton, flotation at the proper level is sometimes a matter of precise adjustment. A very small discrepancy
in adjustment may result in the following chamges.(1) too great buoyancy, causing the organism to rise to an
unfavorable level or even to rise to the surface. Owing to various hazards such as excess light, entanglement with the
surface film, and evaporation; or (2) sinking to an unfavourable depth at which such features as reduction of effective
light, critical reduction or absence of oxygen, and absence of proper nutritive materials may result seriously. Such
adjustment is thus of vital importance to certain nonmotile plankters. This adjustment follows the seasonalchanges of
viscosity and density of water in such a way that organisms may continue to thrive is one of the marvels of aquatic life.
Water fleas swim intermittently but unceasingly, and certain microorganisms occupy proper levels by constant
vibrations of flagella or cilia.
Body form adjustments
a) Streamline form
When a body is either in motion through quiet water or stationary in moving water,the water imposes some resistance
over the body. Hence,the organism has to overcome this force to maintain its stationary position.
A body must occupy space by complete displacement of the water and that when either the body or the water moves; the
body continues the process of displacement. Also, under these conditions, not only must the great weight (density) of
the water be overcome in pushing it aside, but the internal friction (viscosity) of the water plus the friction of the water
against the surfaces of the object must also be overcome. Thus, energy is expended by the object in overcoming these
resistances,and, as will be shown later, the amount of this energy depends upon the form of the body when other
conditions are the same.
Viscosity and density of water vary with certain conditions, particularly temperature; the resistance met by a moving
organism or by an organism maintaining its position in moving water is considerable under all circumstances.
Organisms vary greatly in their ability to overcome this resistance,owing to inherent differences, especially the form of
the body. Obviously, certain forms of body are more effective for locomotion in water than others.
Among other things, it was found that the body consists of two principal parts: (1) the entrance or fore body, that part
from the tip of the snout to the maximum transverse section; and (2) the run, or after body, that portion from the
maximum transverse section to the tip of the caudal fin. It was also found that, in all specimens, the average position of
greatest transverse section occurred at a distance of about 36 per cent.
The replacement of water following maximum displacement had something to do with the function of the after body.
Principle of streamline form
A body with streamline form moving through standing water and the same body maintaining a fixed position in running
water present the same essential conditions.
The position of maximum transverse section represents the maximum displacement of water. it likewise determines not
only the maximum energy expended in displacement but also the termination of virtually all energy expended in
displacement but also the termination of virtually all energy expenditure so far as body surface is concerned.
(b) Other forms of adjustment
Some animals living in the strongest currents possess spines on the exposed surface (Blepharoceridae). These projecting
structures would be detrimental by increasing the resistance. These roughnesses actually help to decrease resistance. In
bodies such as spheres and cylinders, the nature of the resistance may change markedly with relatively small changes in
the conditions involved; at certain velocities, the resistance of a sphere may be reduced by roughening its surface. In
some of the species, spines will be developed as a means of diminishing the resistance to the fierce currents in which
they live. The spines on such a body would increase the resistance at some water velocities but would decrease the
resistance at certain higher rates of flow.
5.3.1. Relations oforganisms to movement ofwater, surface film relations
Relations oforganisms to movements ofwater
Movements of water,in the various forms, affect aquatic organisms in many ways, directly or indirectly, and often play

33
very important roles in aquatic environments.
a) Effects upon sessile animals
Different growth forms in the same animal are the result of presence or absence of water currents or movements
especially in fresh water sponges.
The unbranched colonies are the result of unfavorable conditions, but this can scarcely be credited when both the
branched and the unbranched forms occur side by side in the same water and on similar supports. Bryozoa have also
been supposed to develop different growth forms in standing and in moving water.
b) Effects upon motile animals
Many motile animals show a definite orientation response to current; i.e., they exhibit either positive or negative
rheotropism. Orientation reaction may be accompanied by locomotor activities, so that certain animals will not only
head upstream but will swim, either maintaining their orginal position or making progress against the current.
Sometimes the response to current depends upon some important event in the life history such as sexual maturity.
Atlantic smelt, established in the upper waters of the Great Lakes, which while essentially a lake inhabiting fish,
becomes positively responsive to current at the onset of spawning season and exhibits spawning “runs” at night into
certain adjacent inland waters flowing into the Great Lakes.
Water in motion imposes pressure against certain surfaces of the animal, and it has been held that equality or inequality
of current pressure on different parts of the body affords the stimulus to orientation of some aquatic animals, which, if
true, furnishes an instance of the direct effect of current.
Certain fishes are supposed to orient in response to visual impressions as they float downstream (Clausen et al., 1931)
but still other fishes have been thought to orient in response to the rubbing of parts of the body on the bottom as the
current make them to floats downstream. The visual theory seems ineffective in those instances of runs at night (smelt)
or in very turbid waters.
Certain phenomena such as morphological or physiological, may either be caused by, or correlated with, movements of
water and their different velocities. A general correlation exists between the rate of flow and the shape of mussels in
eastern Bavaria.
Current demand
Certain aquatic organisms exist permanently only in the presence of appropriate movements of water,and it is now
known that current is demanded by some of them. For example, black-fly larvae (Simulium) of all species (one possible
exception in Asia) inhabit only in rapidly running water. Wu (1931) has shown, among other things, that these larvae
possess an inherent demand for current and that their universal absence from standing waters is due directly to the
absence of the necessary current.
Secondarily, current is also related to Simulim larvae in such matters as proper food delivery and respiration.
Resistance to water movement
In general, animals which meet this problem successfully do so by means of one or more of the following features: (1)
body form which offers least resistance,such as the streamline or the hemistreamline form; (2) unusually well
developed burrowing or clinging habit; and (3) special forms of attachment to fixed, supporting objects.
A few may maintain their position because of unusually effective attachment devices (powerful adhesive suckers of the
larvae of Blepharoceridae.
Provisions for clinging and attachment
Among the numerous, special provisions for increased efficiency in maintaining position in the face of strong water
movement are the following:
1. Strong, recurved tarsal claws.
2. Exceedingly flat ventral surface.
3. Strongly depressed body.
4. Lateralmargins of head and thorax produced in the form of flat margins for increased contact with the supporting

34
object.
5. Legs, when of large size, flattened horizontally and applied by their sides as well as by the tarsi to the supporting
object.
6. Special flattening of gills or the modification of the entire gill series to form a ventral attachment disk.
7. Special sucking disks. Examples: blepharocerid larvae; leeches; nymphs of May fly, Ephemerella doddsi.
8. Ventraladhesive pads, often bearing recurved spines. Examples: certain stream inhabiting aquatic Hemiptera and
May fly nymphs.
9. Terminal attachment disks. Example: Simulium larvae posterior disk a combination of a row of hooks with a
gelatinous secretion originating from the mouth.
10. Threads which anchor the animal directly to the support. Example: thread used by Simulium larvae when shifting
position.
11. Threads which anchor case or shelter of animal. Example: certain caddis fly larvae.
12. Shelters, tubes, or cases which protect against the wash of currents and waves. Examples: sand constructed case of
caddis fly, Molanna; cases of certain midge larvae; egg capsules of leeches; tubes of tubificid worms.
13. Adhesive secretions. Example: common hydra.
Provisions for burrowing
Burrowing is often accomplished by animals having no special structural provision for that purpose. In such instances,
they are merely capable of forcing their way into bottom materials, aided by such features as
(1) more or less pointed anterior end; (2) body movements of a penetrating sort; (3) setae; (4) longitudinal contraction
and extension of a portion of the body; (5) extensile and protrusible body tubercles; and (6) strongly muscular body
walls accompanied by freely moving, soft, internal organs and fluids. By such means as these,some of the softest
bodied aquatic animals (Oligochaeta and others) penetrate the hard packed sand of barren, exposed shoals, thus
maintaining their position in the presence of the strongest wave action.
Other animals have developed special structural features for effecting partial or almost entire penetration of bottom,
such as
(1) the flattened, shovel like, anteriorly directed front legs, the posteriorly directed hind legs deppressed to the body and
adapted for pushing, and the pointed sloping head of the nymphs of the May flies Hexagenia and Pentagenia, and the
dragon flies Gomphus; (2) the long, upturned, mandibular tusks of burrowing May fly nymphs; (3) the muscular foot of
clams and snails; (4) the long, spraddling, spider like legs of certain dragon fly nymphs (Macromia), so oriented on the
body that they rest full length upon the sand and, wriggling movements, work the sand entirely over them thus gaining a
certain anchorage; and (5) the strikingly flattened, shoal inhabiting dragon fly nymphs (Hagenius), which weight
themselves down by working sand on top of the thin abdominal margins.
Burrowing by some species may be a direct response to excess light, but the end result of maintaining position remains
the same.
Habits facilitating resistance to water movement
Animals, which, lacking special structural developments, manage to maintain position in current or wave-swept areas by
reactions. These are exemplified by the habitual seeking of (1) the protected sides of and the interstices between rocks;
(2) fissures in bottoms and bottom materials; and (3) the more protected parts of rooted plants.
Influence on construction activities
Construction processes of certain animals can be properly performed only in the presence of water movement. A
striking instance is that of the net building caddis fly larvae which can produce their nets only in moving water; in calm
water,the attempt results only in a shapeless mass of threads.
Distribution oforganisms
Since moving water is an effective transporting agent, movements of water play a very active part in the distribution of
many aquatic organisms. Pieces of aquatic plants bearing various eggs, larvae, pupae, and even adults of insects, hydra,
Bryozoa, Mollusca, and many others break from their attachments and drift with the water.
Molar agents

35
Sand, fine gravel, rocks of various sizes, and sometimes even boulders, carried or rolled by the water,become a
veritable wearing, grinding, fragmenting machine which constitutes one of the serious menaces to the whole biota of
those situations.
Indirect effects ofwater movement
Water movement is concerned with the life of aquatic organisms in a number of ways,the following being among the
most important:
1.Constant shifting of bottom materials on shoals and other shallow waters may prevent the rooting and, therefore, the
occupancy of these areas by higher aquatic plants.
2.Erosion or transportation of materials may completely alter the environment, converting it into some very different
type for which the organisms are not suitable. The example of the cutting off of a sand-spit beach pool from the body of
a lake.
3.Circulation, and in some instances the return to circulation, of essential nutritive substances in the water,both
dissolved and suspended.
4. Production and maintenance of turbidity thus affecting the light penetration and certain other relations.
5.Delivery of food to sessile or sedentary animals, particularly when the food is in the nature of suspended, living
organisms (plankton) and suspended, finely divided, nonliving materials.
6.Respiratory relations, such as (a) renewalof properly oxygenated water to respiratory surfaces and (b) renewalof
dissolved oxygen supply from the air by the surface agitations incident to water movement.
7.Temporary exposure to air, as in seiches which imitate the ebb and flow of a tide and which, if of sufficient
magnitude, may expose for a time a whole set of shallow water organisms to evaporation and other serious hazards.
Surface film relations
The surface film serves as a mechanical support for organisms and miscellaneous particulate materials. Both surfaces of
the film may function in this way. The term neuston, originally applied to minute organisms, is now commonly
extended to include all organisms associated with the surface film. Those related to the upper surface of the film
comprise the supraneuston; those related to the lower surface,the infraneuston.
The larger animals commonly associated with the supraneuston are:(1) water striders (Gerridae); (2) broad-shouldered
water striders (Veliidae); (3) water measurers (Hydrometridae); (4) hebrids (Hebridae); (5) mesoveliids (Mesoveliidae);
(6) whirling beetles (Gyrinidae); (7) springtails (Collembola); and (8) certain spiders.
5.3.2. Relations oforganisms to Temperature relations, Light relations
Temperature relations
With the exception of the aquatic birds and mammals, all aquatic animals are cold blooded (poikilothermous), i.e., their
internal temperatures follow, usually within close limits, the temperatures of the surrounding medium. It must be
understood, however,(1) that exceptions in the form of unusual deviations from surrounding temperatures may occur,
as, for example, the claim that certain fishes may have an internal temperature of as much as 10°C. higher than that of
the surrounding water; and (2) that the degree of agreement between body temperature and external temperature may
differ with the temperature level of the latter.
Some aquatic animals live in surroundings the temperature of which is below freezing (glacier worms and others), but it
has usually been supposed that the freezing point of their body fluids is depressed by substances in solution. Even if this
is true, there remains to be explained the fact that under those very low temperatures they are not only active but grow,
develop, and reproduce.
Influence on metabolism
Within the ordinary temperature limits for a given cold blooded animal, decreasing temperatures diminish metabolism,
and vice versa,a relation which is opposite that for warm blooded animals. This means that metabolic rate is, to a large
extent, governed by the external temperatures. It also means that the falling temperatures of increasing depths in water
or of increasingly northern latitudes inflict lower rates of metabolism. A general rule for this change in metabolism in
cold blooded aquatic animals can be stated as follows: a rise of 1°C increases the rate of metabolism about 10 per cent.
This means that the rate of oxygen consumption and carbon dioxide output doubles with a temperature increase of 10°C.
Influence on development and other biological processes
Rising temperature increases the rate of (1) development of animals, (2) respiratory movements, (3) heart beat and
circulatory rhythms, (4) enzyme action, and (5) other physiological process,although the operative limits in each
process may differ. A cold blooded aquatic animal may be expected to complete its life cycle more slowly and to

36
produce fewer generations per unit of time in the northern than in the southern part of its range; like wise, the normal
individual life span may be longer. Onset of hibernation, breeding season, changes in reproductive activity, germination
of asexual reproductive bodies, and a host of other biological activities are profoundly influenced by surrounding
temperatures.
Temperature toleration
Each organism has a maximum and a minimum environmental temperature between which life is possible but beyond
which conditions are lethal. Even for individual species,these temperature limits are not absolutely fixed, since they
may vary with different individuals, with the different sexes,with different life history stages, with different
physiological states,and in different parts of the geographic range. In spite of this variation, it is possible roughly to
divide animals into two groups: (1) those which are restricted to a narrow range of temperature change (stenothermic
animals) and (2) those which tolerate a wide range of temperature change (euthermic animals). Also, there are
integrades between these two groups. It is a well known fact that acclimatization can shift temperature restrictions as
well as those of other environmental factors. Somewhere between the maximum and minimum limits, an optimum
region occurs, the position and extent of which vary with different animals. It is sometimes stated that the optimum is
usually closer to the maximum than to the minimum, but in some instances the reverse condition prevails.
Acclimatization may also affect the position of the optimum.
In temperate lakes of the first and second orders, only the non-migrating, profundal bottom organisms live under
approximately a fairly even temperature throughout the year. On the contrary, those surface water forms which remain
active throughout the year must endure the complete range of temperature. Those not active in all seasons have
developed various forms of hibernation, and aestivation, as a means of passing over the more rigorous conditions. Many
aquatic animals remain active thorough wide ranges of temperatures,the active period ending only just before the
extremes are reached.
Effects ofextremes oftemperature
The specific effect of extremely low temperature is usually considered as being mainly mechanical, while that of
extremely high temperature is principally chemical, affecting the protoplasm. The chemical effect of excessively high
temperature is more severe than the mechanical effect of correspondingly low temperatures. It is true that even in the
temperate latitudes, certain aquatic animals (mosquito larvae and others) may be frozen into surface ice and recover on
release. This phenomenon seems to be more common in the arctic and subarctic regions.
The occasional rise of surface water temperature to unusual heights (although only a few degrees above the usual
summer maximum) in protected bays in times of clear, hot weather and dead calm water promptly leads to a dying off of
surface plankton and certain other shallow water organisms.
Recognition oftemperature differences
Some aquatic animals have a well developed recognition of changing temperature and may respond with considerable
precision. Under experimental conditions, certain fresh water animals have been found to recognize temperature
differences of 0.2°C and react to them.
In thermally stratified lakes, it is very difficult to determine the presence or absence of a limiting effect to downward
distribution by the steep thermal gradient in the thermocline, since other varying conditions are simultaneously present,
such as light, chemical stratification, and viscosity changes.
Light relations
The various relations of sunlight to aquatic organisms may be classified into two sets: (1) direct influences upon the
organisms as a whole and (2) photosynthetic relations.
Direct influences
Lethal effects
Many aquatic organisms are sensitive to the higher intensities of sunlight and, in fact,must avoid them by occupying
deeper levels in the water.

37
Plankton organisms occur in surface waters,exposed to the maximum light intensity. Many are phytoplankton and have
photosynthetic relations, but it is a well established fact that in most natural waters the maximum populations of
plankton occur at some lower depth, one of the important reasons being the more favorable light effects.
Both sunlight and ultraviolet light seemed to devitalize the diatoms (excepting Synedra) but stimulated the
Chlorophyceae and the Myxophyceae, the ultra violet light providing a slightly greater stimulus. Since the ultraviolet
light is quickly absorbed in the surface waters,its effects are very restricted.
Many aquatic organisms, especially bottom inhabiting forms, live in conditions of almost if not complete darkness and
quickly succumb in direct sunlight. Light is often a powerful factor,sometimes the determining one, in the distribution
of organisms in aquatic environments.
Behavior and orientation
Responses of aquatic organisms are often due to, or conditioned by, light. One of the most striking results of the
alternation of day and night is the migration of certain plankton organisms from deep water to the surface at night and
their return to the depths near dawn.
Light is the principal motivating influence of this migration. For some organisms, day is the period of general activity,
night the period of quiescence; for other forms, the reverse is true.
In many aquatic animals, the light responses differ markedly with physiological state,age, life history stage, season and
other conditions.
Other influences
Direct influences of light effects upon pigments and pigment production, upon growth, upon development, and in fact,
upon many of the conditions involved in the general success of organisms.
Photosynthesis
One of the most profound influences of sunlight (and of moonlight to a limited extent) in water is its intimate role in the
photosynthetic processes of all chlorophyll bearing, aquatic plants.
These plants furnish, directly or indirectly, the carbohydrate and the protein supply for the aquatic world. They occupy
that strategic position between the inorganic and the higher organic components which makes the latter their complete
dependents. The phytoplankton has been called the green pasture of the sea,and it plays a similar role in fresh waters
too.
It becomes increasingly clear that the process commonly referred to as photosynthesis is a very complex phenomenon.
Light, temperature, solutes, and carbon dioxide affect simultaneously the photosynthesis. However,it seems certain that
light of the appropriate kind and intensity is the supreme factor.
Light requirements
The light supply has two important aspects: (1) light intensity and (2) effective wave lengths.
Intensity
The rate of photosynthesis increases with the intensity of light and infact, if certain conditions of temperature and
carbon dioxide are met, the rate of photosynthesis is proportional to the intensity of the incident light. However, the
rates of photosynthesis differ in different plants.
1.Ultraviolet rays are of little or no consequence in photosynthesis. This has been demonstrated experimentally with
terrestrial plants. Considering the fact that ultraviolet waves are completely absorbed in the uppermost, thin layer of the
water and that various aquatic plants thrive far below the level of disappearance of these wave lengths, the aquatic
situation seems to offer confirmation of the statement.
2.Experimental evidence appears to show that with equal intensity of incident light, photosynthesis is affected by
different wave lengths, being greatest in the red and least in the blue violet. Certain investigators claim that the rate of
photosynthesis diminishes with decreasing wave length.
Effective light penetration
The normal existence of healthy chlorophyll bearing plants at various depth levels in water may be taken as evidence

38
that some of the effective light is present in sufficient intensity to enable these plants to perform photosynthesis.
Algae have been found in certain mountain lakes below a depth of 400m and at greater depths in the ocean, but it
remains to be conclusively demonstrated that these plants are performing photosynthesis.
It seems certain that light is a very influential factor in determining the occurrence and distribution of chlorophyll in a
lake. Therefore it may be expected that since light conditions differ in different waters the quantity and activity of
chlorophyll will be influenced correspondingly. Nevertheless the processes of light penetration and photosynthesis in
natural waters are so complex.
The maximum rate of photosynthesis in lakes in full sunlight usually occurs somewhere below the surface layer.
Plants inhabiting situations having moderately reduced light intensity usually have more chlorophyll than do those
living in full sunlight.
That light intensity at which oxygen production in photosynthesis and oxygen consumption by respiration of the plants
concerned are equal is known as the compensation point, and the depth at which the compensation point occurs is called
the compensation depth. For a given body of water this depth varies with severalconditions, such as season, time of day,
degree of cloudiness of sky, condition of the water,and taxonomic composition of the flora involved. As commonly
used the compensation point refers to that intensity of light which is such that the plant’s oxygen production during the
day will be sufficient to balance the oxygen consumption during the whole 24hr period.
Photochemical nitrification
An indirect effect of sunlight is through a possible photochemical nitrification. A portion of the nitrification which goes
on in the sea is photochemically activated. Some chemical nitrification in soil is activated by sunlight in the absence of
the biological agencies.
5.4. Relations ofDissolved Oxygen, Relations ofCarbondioxide
Relations ofDissolved Oxygen
Oxygen supply in air and in natural waters affords a striking contrast. Normally, air contains oxygen to the extent of
approximately 21 per cent, which is an abundant supply for the respiration of air breathing organisms.
One liter of water will contain only about 9 cc of oxygen when saturated with this gas, whereas a liter of air will have
210 cc. In view of the active interplay of oxygen producing and oxygen consuming processes in inland water sets the
stage for serious limits in aquatic respiration.
Excess of oxygen
Moderate supersaturations of dissolved oxygen occur in natural waters from time to time, usually owing to the
photosynthetic activities of large masses of green plants in very calm water. Under specialand still rare circumstances,
large accumulations of excess oxygen appear in the upper part of the thermocline or in deeper strata of a lake.
Normal dissolved oxygen requirements
In the dynamics of natural waters,oxygen supplying and oxygen consuming processes are in constant action, the limits
of an adequate supply of dissolved oxygen for organisms become an important matter.
The minimal oxygen requirement may be affected some what by other environmental features,e.g., temperature,CO2
and certain conditions existing within the organism itself such as age or life history stage. In general “dissolved oxygen
at levels of 3ppm or lower should be regarded as hazardous to lethal under average stream and lake conditions; and that
5ppm or more of dissolved oxygen should be present in waters,if conditions are to be favorable for freshwater fishes”.
This statement assumes,of course,that other vital requirements are maintained within their proper limits. It also applies
primarily to warm water fishes. It has been claimed that cold water fishes require a higher dissolved oxygen content.
The respiration of aquatic organisms depends not only on the dissolved oxygen content but also in a significant measure
upon the temperature of the surrounding water; that the oxygen consumption is almost doubled by a rise of 10°C; that
the same amount of dissolved oxygen has about twice as great a supply value at 5 as at 15°C.
Source of oxygen supply
1.Storage of oxygen
The hemoglobin of the blood may act as a storehouse for oxygen that such storage at times of abundant free oxygen may

39
furnish the supply during oxygen deficiency.
2.Internal chemical transformation
The idea of chemical transformations taking place within the animal, such as occur in the utilization of foodstuffs in
which oxygen is released and made available for recombination.
3.Catalysts facilitating oxygen absorption
Many profundal bottom animals have manganese in their tissues. This element may serve as a catalyst, facilitating
oxygen absorption at low tensions.
4.Atomic oxygen from decaying plant tissues
The decomposing plant tissues in the profundal mud, even under anaerobic conditions, gradually liberate small amounts
of an oxidizing substance could be utilized by the animals living in such close relationship to the decaying plant debris.
Temporary anaerobiosis
Animals living in the muddy bottoms of shallow water or other similar conditions in which the oxygen exhaustion
occurs quickly and for limited times, may be forced to meet these temporarily unusual conditions.
Certain representatives of Protozoa, nematodes, earthworms, leeches,and immature stages of insects, mollusks, fishes,
and others exhibit this ability.
During oxygen lack a certain amount of energy may be released by the splitting of carbohydrates into reduced
substances,thus building up an “oxygen debt,” this debt being repaid by the increased rate of oxygen consumption when
the organism is returned to aerobic conditions.
Some effects of insufficient dissolved oxygen
1.Attempts to migrate
In lakes, it is usually an upward migration into overlying, better oxygenated waters.
2.Onset of diseases
A close relation between insufficient dissolved oxygen to diseases of fishes, parasitic and bacterial and serious
epidemics in the fish Leucichthys artedi, which seems to occupy the cooler water below the thermocline during summer.
3.Suffocation beneath ice cover
Shallow waters with bottoms containing large amounts of putrescible matter and occurring in regions where prolonged
ice cover in winter is common may, at times, almost or completely exhaust the dissolved oxygen of the unfrozen water
with resulting mortality (winter kill) among the organisms.
4.Summer kill
Critically low dissolved oxygen and unfavorable temperatures have been suspected as causalagents,but the case is not
clear since other conditions were probably in a simultaneous state of flux. Warm waters reduced solubility of DO and
release of oxygen by warm waters (less holding capacity).
Relations ofCarbon Dioxide
General effects on organisms
Carbon dioxide is one of the most important substances in the life of organisms.
Small quantities
Usually, the quantities in the air are very small but yet sufficient for the photosynthetic activities of chlorophyll-bearing
plants. Likewise, in natural waters,the amounts may be very small in the upper circulating waters.
Large quantities
Large quantities of carbon dioxide usually have a detrimental effect. Ordinarily, accumulations in unpolluted, natural
waters do not reach such lethal amounts, owing to the ease with which they are released into the air or combine
chemically. Increasing amounts of free carbon dioxide in association with other decomposition products may gradually
render the hypolimnion untenable by all organisms save the resistant anaerobic animals in the bottom.
Such accumulations may render bottom waters acid in reaction and thus affect organisms sensitive to acid waters. High
carbon dioxide content seems to be more toxic in the presence of low oxygen content.
Since an excess of dissolved carbon dioxide is usually accompanied by a much reduced dissolved oxygen content and
other important conditions, it has been proposed that the carbon dioxide content of the water is probably the best single
index of the suitability of water for fishes.
Carbon dioxide has a very definite effect upon the affinity of blood for oxygen in fishes and certain other animals.
Fishes may tolerate wide, but not sudden, ranges of carbon dioxide tension of the water by “increasing the alkali reserve

40
of their blood in high carbon dioxide tension water and by lowering the alkali reserve of their blood in low carbon
dioxide water”.
Carbon dioxide tension
While the carbon dioxide tension within natural waters and within the atmosphere constantly tends toward equilibrium,
circumstances prevailing in the water (slow diffusion, rapid production of carbon dioxide, insufficient agitation of the
water) may be such that at some depths the carbon dioxide tension is greater than in the air.
Relations ofother Dissolved Gases : Methane, Hydrogen Sulfide
Methane
Some have claimed that it is nontoxic; others, that its effects on organisms are minor or that, at most, it may be
occasionally toxic to animals or that it may cause them to migrate from particular situations. Possibly methane
accumulations in bottom waters may have something to do with the increasingly severe conditions which develop with
the progress of stagnation periods.
Hydrogen sulfide
Inherently, hydrogen sulfide is very poisonous. Certain marine fishes are said to be very sensitive to this gas and to
avoid water containing it.
5.5. Nitrogen, Ammonia, Dissolved solids, Other elements, Dissolved organic matter
Nitrogen
Free nitrogen has usually been supposed to be the least important of the dissolved gases when it occurs in normal
quantities. Excess nitrogen is said to cause gas disease in fishes. Unusual amounts may produce entry of the gas into the
circulatory systems of aquatic animals, causing stoppage.
Ammonia
Scanty information is available on the biological relations of gaseous ammonia as produced in natural waters.
Dissolved solids
Relations of inorganic nitrogen compounds
Ammonium salts, nitrites, and nitrates furnish a supply of nitrogen which is essential in the fundamental food relations
of organisms. Ammonium salts (“ammonia nitrogen” or “free ammonia”) constitute the first stage in mineralization of
organic nitrogen. It is usually considered that nitrates supply nitrogen in more available form, although the other two
compounds, particularly ammonium salts, are utilized to some extent.
While some plants seem to prefer nitrates, there are others which grow equally well with both nitrites and ammonium
salts. Variations in the quantities present in water are correlated with the growth seasons of plants and with the
temperatures which control, to some extent, the rate of bacterial action. Ordinarily, nitrogen in its final oxidized form as
nitrate does not occur in great amounts in natural, uncontaminated waters. The Algae, water weeds,and nitrate reducing
bacteria are the important consumers of nitrogen content and that the nitrifying bacteria aid in increasing the nitrate
content. Nitrogen is considered to be one of the most important limiting factors in the development of phytoplankton. It
is one of the nutritive substances necessary for the production of chlorophyll. Formation of chlorophyll ceases very
quickly with nitrate deficiency. Ammonium salts in excess are reported as poisonous to fishes if present with
carbonates.
Relations of silicon
Since diatoms require silicon for the manufacture of their shells, and since they constitute a very prominent and strategic
group in the plankton at large, the available supply of silicon in the water is regarded as a matter of importance. The
production of diatoms is directly determined by the silicon supply. Silica deposition by diatoms is a one way process;
that silica in the form of diatom shells is highly resistant to passage into solution in water; that diatom shells once
formed are practically permanent in many waters. Silicon removed from sea water by diatoms and other organisms may
return to solution after they die, or it may sink to the bottom.
Development and success of the fresh water sponges depend upon an adequate supply of silicon for the manufacture of
spicules. Some permanent loss of silicon is expected,in average situations, owing to transportation by currents, to
outlets, and to burial in bottom deposits. In the presence of such losses, a source of renewal is necessary if a body of
water is to avoid silicon decline to a critical level.
Relations of phosphorus
Since the amount of soluble phosphorus in natural, unmodified waters is small and since phytoplankton requires an
adequate supply of phosphorus, it is now generally regarded as a limiting factor. Phytoplankton occupies the upper

41
waters because of their light requirements die and sinks to the bottom, carrying away a certain amount of the
phosphorus. Restoration of phosphorus to the upper waters might be brought about by inflow of waters rich in
phosphate or by the return to circulation of the phosphorus containing materials, return of which would be facilitated by
overturns or other forms of circulation.
The nitrogen phosphorus ratio
The relation of these two substances is better known for sea water than for fresh water. The concentrations of the two
substances closely parallel each other. In sea water it appears that the ratio tends to approach a constant value, with
nitrogen exceeding considerably the phosphorus content, and that as claimed these substances occur in marine plankton
in about the same proportions. Further, the ratio in inland waters may be different not only in numerical value but also in
the range of deviation from proposed mean. This matter is still in the pioneering stage,but is suggestive of basic
limnological possibilities and deserves more investigation.
Other elements
The significance of severalother elements appears most prominently in their essential roles in the metabolism of the
various groups of aquatic plants. Calcium is required by all green plants except some of the lower Algae; is not
necessary for the fungi; and while necessary for the non-chlorophyll flowering plants, they usually contain less calcium
than do chlorophyll bearing ones. It appears to have severalphysiological roles, such as (1) relation to the proper
translocation of the carbohydrates; (2) an integral component of plant tissue; (3) facilitation the availability of other
ions; and (4) an antidoting agent reducing the toxic effects of single salt solutions of sodium, potassium and magnesium.
Magnesium is a component of chlorophyll and must be present for its proper development. It appears to act as a carrier
of phosphorus, at least in some instances. Quantities of magnesium larger than usual in natural waters may be toxic to
some aquatic organisms. Cladocerans are wholly absent from certain lakes (Lake Tanganyika, Lake Kivu) may be
owing to the excess of magnesium over calcium salts.
Iron must be supplied for plant growth and development. It functions in the proper production of chlorophyll, although it
does not enter into the chemical composition of chlorophyll. It acts as a catalyzer; others, that iron is the oxygen
carrying substance in certain respiratory processes. Both the quantity and the form in which it is presented to the plant
are now known to be important, these being conditioned by the features of the environment (hydrogen ion
concentration, organic matters,and others) and the kind of plant involved. Most algae grow best when the water has a
ferric oxide content of 0.2 to 2 mg/litre, but distinct toxicity occurs when the available iron exceeds 5mg. however,
many natural waters may contain more than 5mg. of iron without being toxic owing to the buffer action of organic
compounds or of calcium salts. Toxic oxidation products of pyrites are said to be formed in peat deposits. Two other
relations of high iron content have received attention in limnological literature: (1) reduction of nitrates to nitrites by
ferrous salts in the presence of oxygen and (2) reduction of dissolved oxygen in the presence of iron.
Sodium, while apparently not absolutely necessary for plant growth and development, is evidently a very desirable
element. It may serve one or more of the following roles: (1) act as a conserver of potassium, since less is absorbed
when sodium is present; (2) replace potassium to a limited extent as a plant nutritive element; (3) render soil-absorbed
potassium more available to plants; and (4) be an antidoting agent against certain toxic salts in the medium.
Potassium is a fixed requirement for plants. Its function is imperfectly known, but it appears to be two fold; (1) a
fundamental requirement in food manufacture and (2) a catalyst. Sulfur must be provided for plant growth and
development. It forms a necessary materialin the composition of protein and other constituents of the plant.
Trace elements
By trace elements is meant those chemical elements essential to the well being of animals and plants but required only
in extremely small quantities. Prominent among these trace elements are copper,manganese, zinc, boron, lead, cobalt
and iodine.
Dissolved organic matter
Many of the minute, more or less undifferentiated organisms, such as the bacteria, certain Algae, and certain protozoa,
must depend upon the dissolved materials in their environments for the substances necessary to growth and
development. At one time, the discovery that many microorganisms use particulate foods cast some doubt on the direct
utilization of dissolved substances by many organisms. However,it has since been clearly demonstrated that bacteria,
diatoms, most if not all other phytoplankton, and some of the Protozoa normally utilize and depend upon both the
dissolved inorganic and the dissolved organic materials in their surroundings. It likewise seems probable that many

42
other small organisms which lack a digestive tract or other provisions for introducing particulate foods will be
discovered to depend upon these materials, wholly or in part.
The plankton in the ocean is entirely insufficient in amount to supply the necessary nourishment for those animals
supposed to depend upon it and (2) that an abundant supply of food is available in the dissolved organic matter in the
water. From computations of the minimal carbon requirements of certain marine animals for a given time unit and
determinations of the plankton content of the surrounding water,he insisted that the amount of water strained by the
animal to secure the minimal amount of carbon was impossibly large. In this way, he showed that a certain common
marine sponge would need to filter 2421 of sea water per hour (about four thousand times its own bulk) to secure the
minimal amount of carbon from the plankton.
The chlorophyll bearing phytoplankton is not dependent upon nitrogen salts or upon carbon dioxide in water for either
nitrogen or carbon but, instead can utilize atmospheric nitrogen dissolved in the water (nitrogen fixation); that the
nitrites, nitrates, and ammonium salts in the water may remain unconsumed and that bicarbonates of calcium and
magnesium can be broken up, the half bound carbon dioxide furnishing a carbon supply for the green phytoplankton.
This reaction, they claimed, is of such magnitude that at the spring plankton maximum, assuming that it occurs to the
same extent down to a depth of 100m., the carbon so provided would be sufficient for a phytoplankton crop of 10 tons
or more per acre,wet weight.
1.Organic detritus and living organisms in water usually provide food in necessary quantity for the aquatic animals
present. Certain protozoa and possibly sponges may absorb dissolved organic matter from the water.
2.The rather large quantities (10 mg. per 1. or more) of dissolved organic matter in fresh water include proteins in
colloidal solution and severalamino acids greatly diluted. Carbohydrates present do not appears to be in readily
assimiable form.
3.Dissolved organic matter seems to be principally waste products, some of which are very resistant to bacterial action.
4.Very little of the organic matter produced by living Algae is given off to the water; 90 to 95 per cent of it is stored in
the organisms.
5.It is possible that higher animals absorb insignificant quantities of the dissolved substances.
6.Experimental evidence is now available which indicates that tadpoles, mussels and probably other animals may take
up dissolved organic matter from rather concentrated solutions and are thus enabled to thrive and grow, at least for a
considerable period of time, in the absence of particulate food.
7.Experiments of certain investigators show that absorption of dissolved organic matter by tadpoles, mussels and
starfish occurs through the intestine and not through gills or integument. The integument and gills of aquatic animals
seem to be, for the most part, impermeable to organic substances.
In general, marine invertebrates are permeable to water,salts, and organic solutes but that teleosts and fresh water
invertebrates are very slight permeability. In Daphnia magna organic substances in true solution were not used for food,
but organic matter in colloidal form was utilized. The fishes may absorb a slight amount of dissolved substance,but the
securing of a large proportion of their nutriment in this way, as has been postulated, appears very doubtful.
Planktonic organisms
6.1. Classifications of organisms in water
Planktonic organisms
The term plankton was first proposed by an Oceanographer, Victor Hensen in 1887 to designate that the
heterogeneous assemblage of minute organism and finely divided, non-living materials which are known to
occur in the waters and to float at the will of the waves and other water movements.
Classifications
Plankton of the various freshwaters differs widely in quality. The following outline is an abbreviated
indication of the organism which may occur in the plankton of fresh water.
1. Plants :
a) Algae are represented in the plankton of inland waters
b) Fungi, which occur as bacteria abundantly in the plankton, in fact it is likely that no water in nature is free
from them.
2. Animals :
a) Protozoa – These are the representative of the plankton by many genera and species
b) Coelenterate - Mainly hydra is facultative plankter occurring at times free in open water
c) Rotatoria is the most important groups of zooplankton

43
d) Gastrotricha - occur in limited numbers
e) Bryozoa whose larvae are free swimming
f) Arthropoda – Mainly i) Crustacea and ii) Insects
3.Occasional plankters :
a) Flowering plants for eg. Wolffia (Lemnaceae) occur at various depth and are recorded as plankton
organisms especially in rivers.
b) Platyhelminthes eg, Turbellaria are of less importance in freshwaters.
c) Coelentrata eg, Medusa (Craspedacusta)
d) Insecta eg, May-fly nymphs
e) Arachnida eg, Water mites
f) Vertebrata eg, Juvenile stages of fishes
Classification and Terminology of Plankton
Some of the important groups of plankton are :
1. Classification based on Quality
A. Phytoplankton – plant plankton
a. Phytoplankton proper – chlorophyll bearing plankton
b. Saproplankton – bacteria and fungi
B. Zooplankton – animal plankton
2. On the basis of Size
A. Meroplankton – the large units of plankton, visible to the unaided eye
B. Net plankton (Mesoplankton) – plankton secured by the plankton net equipped with No. 25 silk bolting
cloth (mesh 0.03 to 0.04 mm)
C. Nanoplankton (Microplankton) – very minute plankton not secured by the plankton net with No 25 bolting
cloth
a) Ultra plankton : <5 µm (<0.005 mm)
b) Nano plankton : 5-60 µm 90.005 – 0.06 mm)
(Dwarf / runts)
c) Microplankton : 60-500 µm (0.06-0.5 mm)
(Net plankton)
d) Meso plankton : 500-1000 µm (0.5-1.0 mm)
e) Macroplankton : 1.0 mm – 1.0 cm
f) Megaloplankton : > 1.0 cm
3.On the basis of local environmental distribution
A. Limnoplankton : lake plankton
B. Rheoplankton (Potamoplankton) : running water plankton
C. Heleoplankton : pond plankton
D. Haliplankton : salt water plankton
E. Hypalmyroplankton : brackish water plankton
4.Based on Origin
A. Autogenic plankton : plankton produced locally
B. Allogenic plankton : plankton introduced from other localities
5.On the basis of content
A. Euplankton / True plankton
B. Pseudoplankton (Flase plankton) : debris mingled in plankton
6.Based on the life history / plank tonic life (Length of time)
A. Holoplankton / Permanent plankton : organisms free floating throughout their life
B. Meroplankton / Temperory plankton : organisms free floating only at certain times or stages of life cycle
7.Based on habitat in water body
A. Hypoplankton : Benthic
B. Epiplankton : Surface
C. Bathyplankton : Aphotic zone
D. Mesoplankton : Disphotic/lighted zone

44
6.2. Distribution ofplankton
In all natural waters irrespective of latitude, longitude and physic-chemical characters majority of normal supporters are
of plankton and differ in great many respects. Occasionally they occur in certain thermal waters,subterranean waters,
spring-fed streams,transient pools etc. The presence of plankton in natural waters is itself an indication of the
significant position which it occupies in the aquatic environment.
General geographical distribution ofplankton
It has been claimed by some of the Oceanographers that the polar seas support abundant plankton than do the tropical
ones. Polar and tropical inland water are still little known limnologically plankton production cannot be compared
satisfactorily. Certain northern low lying lakes in countries bordering on the Baltic sea,plankton production in the
inland water of North American is little known.
Horizontal distribution of plankton
There is irregularity in horizontal distribution of plankton in water. One of the most common causes of irregularity is the
wind acting upon surface waters. Plankton drifts due to wind action are always temporary and is common in many
inland waters. This drifting leads to meeting towards the shore becoming so thick that the whole water colour is altered
and changes the general appearance. The generaleffect of drift is to concentrate more or less upper waters throughout
one part of a water body with corresponding thinning on the opposite side.
Other important factors which are responsible for horizontal distribution of the plankton are :
a) inflowing streams
b) irregularity of shore line
c) depth of water
d) flowage areas
e) water current etc.
Wind is one of the most common causes of irregularity in horizontal distribution of plankton. Since wind causes waves
but in addition may produce an actualdrift of the upper waters. But under certain conditions of drifting water,plankton
organisms become concentrated temporarily in the vicinity of the shore which faces into the wind at that time.
Vertical distribution of plankton
The vertical distribution of plankton is a complicated matter. In deeper region, plankton may show little or no
resemblance to that of upper waters. In lakes, a uniform vertical distribution of plankton occurs only during Spring and
Fall overturns but certain plankton are distributed in minimal quantities from the surface to the lowermost limits of
habitability in the range of concentration that they occur.
Distribution of phytoplankton
The upper most waters are the home of the chlorophyll bearing plankton and perhaps the light plays an important role
indicates the distribution of phytoplankton. Considering the general mass distribution, few stalemates are commonly
taken such as :
a. The blue green and green phytoplankton (Myxophyceae and Chlorophyceae) concentration is maximum than diatoms
and this has been thought to be due to the heavier weight.
b. Maximum populations of chlorophyll bearing phytoplankton are at some level below the surface waters.
c. The blue green algae as a group tend to concentrate towards the surface.
Distribution ofzooplankton
It is difficult to generalize on the vertical distribution of zooplankton as a whole and the same is true of the various
taxonomic groups composing the zooplankton. Certain tendencies in vertical distribution appear such as :
a. Greater occurrence of Sarcodina in lower waters
b. Preference of Dinoflagellata for upper water
c. General scattering of Ciliatei and
d. Selection of different levels by the young and adult stages of certain crustacean
The distribution behavior may be very different in different kinds of water. Under conditions of well developed physic-
chemical stratification, the levels of maximum population of the Crustacea and Rotifera often correspond closely,
although such a statement cannot be dependent upon.
Conditions influencing vertical distribution
Among the influences which may operate in the production of various forms of vertical distribution, the following are
important a) Light b) Food c) Dissolved gases d) Temperature e) Wind f) Gravity g) Age of individuals of a species.
1. Light is the most important factor in vertical distribution of plankton and is well established. Its presence for various
reasons tends to removal or sometime disappearance of plankton. The annual and diurnal variation of light, qualitative
and quantitative variation influence the migration of plankton Differences is light reaction of young or adult stages of
certain plankters lead to a different vertical distribution of the life history stages in the same species.
2. Food - The abundance and availability of zooplankton also depends to same extent by the distribution of food. It has
been wall established that the concentration of protozoa, micro crustacea and rotifers have been correlated with the

45
presence of settling suspended materials.
3. Dissolved gasses and other substances - Dissolved oxygen is an important part in rendering deeper waters partially or
wholly uninhabitable for most of common zooplankters. Some zooplankters are more sensitive than others to the
accumulating results of decomposition in underlying waters so that all which do not retreat upward at the same rate and
certain stratification may result. But nevertheless, the chemical changes progress to the lethal point for pelagic plankton
organisms eventually eliminating from underlying waters.
4. Temperature
Direct effects :
a) selection by motile plankters of favorable temperatures or
b) inability of non-motile forms to exist in levels having certain temperatures.
Such effects appear to apply only to those plankters which manifest sensitively to differences in temperature while many
plankters are not influenced at all by any of the vertical temperature differences within a lake.
Indirect effects : changes in density and viscosity of water altering the floatation levels of those plankters which are
adjusted to floatation.
5. Wind – its effect is significant with the season. During summer, directly influence the epilimnion and during hard
blows vertical distribution of plankton is seen. During Autumn and Spring overturns, wind disturbs plankton because of
same density and viscosity throughout but during the period of ice cove, the disturbing influence of wind is eliminated
6. Gravity – reduction of specific gravity makes certain phytoplankton such as Gloeotrichia to congregate at surface
waters. Plankton especially the pelagic crustacean are heavier than water and sink with appreciable speed when inactive.
Daphnia maintain their position in water.
7. Age ofindividual of a species – as a generalrule, young individuals occur near surface,adults tend to sink into
deeper waters.
6.3. Food for plankton organisms
Plankton contains miscellaneous assemblage of organisms which are fairly high in animal scale, food requirement are
diverse and can be considered best in connection with individual group.
Green phytoplankton: Chlorophyll bearing phytoplankton utilise organic and inorganic materials dissolved in water.
Certain chlorophyll bearing Protozoa utilize certain amount of particulate materials.
Non green phytoplankton: They do not possess chlorophyll such as bacteria depend upon dissolved materials.
Protozoa: The protozoan plankters feed upon minute algae and bacteria. Utilisation of dissolved substances has been
demonstrated in certain protozoa.
Metazoan – Neumann (1929) considered the relation of zooplankton as seston feeders into the 4 types viz.
1. grasping type : such as Rhizopoda which touch and secure seston with pseudopodia
2. filtration type : filtering of seston from water as animal moves
3. sedimentation type : capture of seston by means of induced water currents and
4. predatory type : capture of other organisms
Cladocera: They obtain food by active filtration of water and by predation. Cladocerans filter their food from water
mainly particulate matter such as inorganic debris, organic debris and living organisms. Experiments showed that
Daphnia and Bosmina took ordinary pond debris, algae, carmine and finely divided humus indiscriminately filling the
digestive tract with mixture.
Copepods: Thorough examination of the digestive tracts of certain copepods have revealed that
a) Cyclops had fragments of exoskeleton of Entomostraca, jaws of rotifers
b) Diaptomus and
c) Nauplii had eaten finely granular mass for minute algae.
Seasonal Changes ofBody Form in Plankton organisms
Morphological character of body form changes
The seasonal change of body form differ greatly in different plankton and the changes from winter to summer forms by
way of increase in body surface compared to body volume.
For eg,
a) the flagellate shows a tendency in summer to have a longer stalks
b) the Ceratium hirundinella develops in summer and produce a longer, narrower body from
c) Cladoceran body in summer is higher than long with a longer back and longer posterior spine and is reverse in winter
season
d) Rotifers show changes in body size, changes in number and development of anterior spines in pond condition which
is less frequently in lakes.
General biological features
The following statements are based largely upon the summary by Wesenberg Lund (1926)
1. Seasonal changes of form is best developed among perennial species during summer and disappear during winter

46
2. Seasonal changes of form may take a different aspect in different lakes due to local variations
3. Transition ie, transformational stages occur almost abruptly over a period of 2 or 3 weeks in autumn but is gradual
from summer to winter periods
4. The body form may not change in different season if it is having same body shape in summer
5. Body form among cladocerans and rotifers is restricted in case of females
Primary productivity
The primary production in the aquatic ecosystem starts with the synthesis of organic compounds from the inorganic
constituents of water by the activity of plants / phytoplankton in the presence of sunlight. The inorganic constituents
which form the raw material for this synthesis are water,carbon dioxide, nitrate ions, phosphate ions and various other
chemical substances. The products are mainly carbohydrates and proteins and fats in very small quantities. Organic
production by plants is the first step in tapping energy by living beings from non-living natural resources and hence
called primary productivity.
The method of estimating primary productivity by dark and light bottle method was introduced by Garder and Gran
(1930). In this method, the water samples are incubated for a certain period in light and dark bottles which are then
suspended at the same depths where from the sample are taken. In light bottles, oxygen is released as a result of
photosynthesis and a part of oxygen is used for community respiration. In the dark bottles, only oxygen consumption
takes place as a result of respiration. The amount of oxygen liberated by phytoplankton during photosynthesis is
considered as a measure of primary production.
The total quantity of organic matter synthesized by a unit measure of plants in a unit time is termed as gross primary
productivity. Some of this material is broken down by plants themselves for their respiration, excretion and death etc.
The reminder which becomes the plant tissue is called net primary productivity.
Factors influencing primary productivity
The rates of photosynthetic primary production by phytoplankton vary greatly in different waters and at different times.
The variation in photosynthetic rates suggests that there are factors that differ from place to place and from time to time,
which determine the evident differences in photosynthetic activity. The major influencing factors are :
1. Light intensity
The radiant energy that reaches the surface reacts with the dissolved and particulate materials present in the water and
this reaction brings about absorption and scattering. Illumination of surface layers varies with place, time, light intensity,
water transparency,diurnally, seasonally and attitudinally and also with cloud condition and atmospheric absorption.
Depending on the conditions, about 50% of the incident light is reflected back; about 80% of the total radiation entering
the surface is absorbed within the upper 10 m. and only about 0.1 to 0.2% is converted into photosynthetic production.
2. Temperature level
Very high temperatures inhibit photosynthesis since they damage the enzymes and cell structure as in photoinhibition.
Relatively hot and light surface layer is more vulnerable to turbulent mixing due to which the algae can be carries down
below the photic zone. At critical depth, the total primary production in the water column above equals the total loss by
respiration in the same column.
3. Nutrient supply
The fundamental importance of nutrients is that the rate at which they are supplied may determine the rate of primary
production. The potential limitations of producer activity by nutrients show that after addition of nutrients, net
production increases. The productivity of the system is nutrient limited regardless of the changes in species composition
that often result from the enrichment.
4. Grazing rate
The biomass of zooplankton generally coincides with minima of phytoplankton density on account of grazing. In some
areas of the water bodies, as much as 99.5% of the net primary production may be grazed. The plankton upon death,
would liberate phosphorous and nitrogen rapidly in the water making it available to phytoplankton growth.
Aquatic plants
7.1 Aquatic plants- Character, classification, zonation, seasonal relations
Character of larger aquatic plants
Larger aquatic plants constitute a heterogeneous group composed of a few Bryophytes and Pteridophytes and
many of the families of Spermatophytes. They are restricted in distribution to the general vicinity of the shores
and to the shallow water areas. The larger aquatic plants of United States are cosmopolitan within the
continent although they are highly specific in habitat requirements.

47
In general, the aquatic plants can be grouped in to 3 assemblages
1. Emergent – those rooted at the bottom and projecting out of the water for part of their length eg, common
species of bulrush, Scirpus
2. Floating - these which wholly or in part float in the surface of water and often do not project above it eg.
Duck weed Lemna and
3. Submerged - those which are continuously submerged eg, Vallisneria.
More or less elaborate grouping or classifications of larger aquatic plants have been proposed from time to
time. Hence, the following classification taken with some modification from Akber’s work on Water plants in
1920, has many point of usefulness.
Biological classification of the larger aquatic plants
A.Plants roots in the bottom
1) Terrestrial plants capable of living at least temporarily as submerged water plants without any marked
adaptation of leaves to aquatic life eg: Achillea ptarmica, Nepeta hederacea
2) Plants sometimes terrestrial, sometimes with submerged leaves but different from aerial type and associated
with flowering stage
3) Plants which produce 3 types of leaf (a) submerged (b) floating and (c) aerial
4) Plants which in certain instances may occur as land forms but normally submerged and characterised by a
creeping axis bearing long, branching leafy shoots with no floating laves
a. Leafy aerial shoots produced at flowering period eg, Myriophyllum
b. Inflorescence raised out of water but not aerial foliage leaves eg. Potamogeton, Myriophyllum
c. Inflorescence submerged but organs raised to the surface eg. Anacharis
d. Inflorescence entirely submerged eg. Najas
5) Plants which may occur as land forms but commonly submerged characterized by an axis forms with linear
leaves arise
6) Plants which are entirely submerged having vegetative either root or shoot naturally attached to the
substratum
B. a) Plants which are not rooted to the bottom but live unattached in the water
1) Plants with floating leaves, flowers raised into the air and roots not penetrating the bottom eg. Spirodella,
Lemna
2) Rootless eg. Wolffia
b) Plants entirely or practically submerged; Rooted but not penetrating bottom eg. Lemna and Rootless eg.
Utricularia, Ceratophyllum
Zonation
It is the most noticeable features of the larger aquatic plants is the distinct tendency in more or less parallel
zones along the margins of lakes ponds and similar body and water.
Smaller lakes or the protected area of the water body and marginal regions of larger lakes the zonation may
exhibit great regularity. A lake margin possessing this typical zonation shows the following sequences :
1) Zone of emergent hydrophytes – Here plants are rooted to the bottom, submerged at the basal portions and
elevated into the air at the tops. It is a shoreward zone extending from near the edge of water lakeward up to a
depth of 2 m. Most commonly found plants include Scirpus (bulrush), Typha (cat tail), Sagittaria (arrow
heads) etc.
2) Zone of floating hydrophytes – This zone occurs beyond (lakeward) the emergent zone comprising plants
which are rooted to the bottom but the foliage float on the surface. The depths occupied somewhat but usually
about 10 cm to 2.5 m. The characteristic plants are water lilies Nelumbo, Nymphaea, Nuphar, pond weed
Potamogeton.
3) Zone of submerged hydrophytes – Typically, this zone occupies deeper water beyond the zone of floating
plants extending downward to a depth not exceeding 6 m. The plants of certain species of pond weed
(Potamogeton), water milfoil (Myriophyllum), Vallisnaria, Najas and others are commonly found in this zone.
Seasonal relations
In regions of well defined winter season accompanied by the development of ice water and plants of emergent
and floating types die down and disintegrate with the onset of winter. This disintegration occurs among the

48
wholly submerged plants and still uncertain and evidences have shown that atleast few of them were in active
condition throughout the year even under the ice.
7.2 Quantities produced, chemical composition, distribution in different waters, limnological role
Quantities produced
Production of aquatic plants varies greatly with the nature of the water. It has been studied in lake Mendota, the
Vallisneria constituted about 1/3rd of the total quantity; while in Green lake it composed < 10% where Chara comprised
roughly one-half of the total quantity whereas in lake Mendota it amounted < 5%. Therefore it has been predicted that
the production of larger plants differ widely both qualitatively and quantitatively.
Chemical composition
During the growth period of plants, temporarily certain essential substances from water and bottom deposits the
chemical composition of plants which may give some information on amount of substances used. Plants make demand
upon the supply of essential materials in the water. The amount of different substances removed or returned to the water
have been studies. The most important ones are Ash,crude protein, ether-extract,fiber and carbohydrates have been
determined.
Distribution in different waters
It is well known fact that the chemistry of water influence in determining general distribution. The qualitative
composition of aquatic flora differs in different types of water bodies in inland areas. The aquatic flora has been divided
into 3 major groups namely
1. soft-water flora
2. hard-water flora and
3. alkali or sulfate-water flora
Limnological role
It is necessary to consider the functions which the larger aquatic plants play in aquatic complex. The relations, direct
and indirect are numerous but the following ones are probably the most important.
a. Utilization of non-living matter
The utilization of mineral salts and CO2 in the building up of green plant tissue needs more emphasis here. It has been
reported that the roots of larger aquatic plants serve primarily as provisions for holdfast having very little physiological
function in absorbing nitrates from bottom and the absorption of nutrient materials is performed mostly by the body of
the securing substances from water only. Some of the plants roots are very much reduced and the function of absorption
is insignificant. However,the function of anchorage has an outstanding role in these plants and like wise the reduction
of absorption by the roots compared with land plants is also established.
b. Food for animals
The role of the phytoplankton in basic food supply has been known but different opinion existed as for as larger aquatic
plants concerned as food materials for aquatic plants. Recent studies have shown that large quantities of these plants are
often consumed by great variety of animals. Berg (1950) studied that about 17 species of Potamogeton have been
consumed by 2 dozen different species of insects. Fragments of larger aquatic plants occur in stomachs of fishes.
Analysis of stomach contents have been reported in certain fishes the plant materials composing up to 50% of the total
food content and hence it is mentioned that some fishes are largely plant feeders. Aquatic birds (ducks, geese),
mammals (musk rat, deer,moose and beaver) secure food from aquatic plants. Nelsom et al. (1930) found that some of
the plants like Anacharis, Myriophyllum and Vallisneria have high protein and carbohydrate content including several
vitamins.
Nekton
8.1 Nekton- Composition, Distribution, Movements
Nekton
The term nekton has been coined by Ernst Heckal (1890). Nekton is derived from Greek word means
swimming. The term nekton is used to designate those organisms which swim freely in water and possess
locomotion enabling them to have independent drifting movement along the water flowage system. In limnetic
regions of inland waters, the nekton is composed almost entirely of fishes.
The limnetic nekton may inhabit the whole of open water of a lake and down to its greatest depth. In contrast
to the limnetic region, the littoral area is the zone of greater nekton population. In addition to the fishes (young
and mature), numerous free swimming invertebrates occur mainly insects. Vegetative zone particularly the
pondweed zone, contain largest nekton population. Major groups of vertebrates including fishes, Amphibia,
Retillia, Aves and Mammalian are more or less representative of water and some time free swimming in
nature.
Composition: Nekton comprises three phyla, viz, chordates, molluscs and arthropods, but molluscs
composition in fresh water is very less in the case of nekton.

49
Among Arthropods the dominant groups comprising Insects and crustaceans are involved. However, the
phylum, Chordata, is the largest group in Nektonic community, mainly fishes, Amphibians, Reptiles, Birds
and mammals.
Distribution
Distribution depends on the following factors
- seasonal changes
- Physiological changes (competition for space).
- Food availability and distribution
- Life cycle - young ones of white fishes goes to the surface for feeding whereas adults inhabit the column
water.
- Formation of local aggregations.
- Seasonal migration
- Diurnal movement
- Reproductive cycle
- Presence or absence of shelter
- Oxygen distribution
- Temperature conditions.
It has been observed that certain fishes select deeper, cooler waters, intermediate regions and some select
upper strata. Such a distribution depends upon the season, physiological state of the fish and the stage in life
history. According to Shelford (1913) in Great lakes, the white fish exhibit horizontal depth stratification and
are arranged one above the other in their distribution. Koelz (1929) claimed that this fish in Great lakes have
shown vertical distribution pattern. In some lakes the species that regularly inhabit shallow water may be
driven by competition on the shoals or by absence of shoals found in the deeper waters eg, lake Ontario. In
lake Nipigon the species inhabiting deeper waters are known to occur in shallow waters are Clupeaformis,
alpenae, zenithicus etc; but Johannae, Nigripinnis and Kiyi found in deeper waters.
The food of great lakes white fishes seams to be secured from the plankton and the immature fish come to
uppermost waters giving them a vertical distribution from that of mature stages. Fishes like lake trout
(Cristivomer namaycush) and turbot (Lota lota) occur in deeper waters.
Like plankton, the nekton also have uniform distribution pattern. They have a complex background of
distribution with regard to seasonal migrations, diurnal movements reproductive cycle, movement of water,
temperature conditions etc.
Benthos
9.1 Classification of benthic regions, beach zones, periphyton,distribution
Benthos
The term benthos includes all bottom dwelling organisms, comprising the great assemblages of plants and
animals. Benthos includes the organisms of the bottom from uppermost water bearing portion of a body of
water right up to the greatest depths.
Classification of benthic regions
The benthic habitat is not uniform and it can be classified into different zones, they are.
1. Lake zone:
There are usually 3 zones and in exceptionally in deep lakes there are 4 zones, they are Littoral, Sublittoral,
Profundal and Abyssal zones.
i) Littoral Zone : Extends from water’s edge to the lakeward limit of rooted vegetation.
ii) Sublittoral Zone : From lakeward limit of vegetation down to about the level of the upper limit of the
hypolimnion.
iii) Profundal zone : The entire lake floor that bounds the hypolimnion
iv) Abyssal : Present only in lakes of depths greater than 600 m.
1.Beach zones
Benthic region was formerly regarded as water’s edge extending to the deepest region. The biota is truly

50
aquatic, living in water at beach and has direct continuity with the main body of the lake or stream and the
organisms involved are benthos and the environment are considered as benthic region. The exposed sandy
beaches maintain 3 parallel environments, they are :
a. The inner beach
b. The middle beach
c. The outer beach
The inner beach extends from water’s edge, during periods of calm water up to the slope to the place where
the surface of sand ceases to be with water and shows the first signs of drying. This zone is narrow and
exposed to the slight wash of gentle wave of calm weather.
The middle beach occupies the space just beyond the inner beach to the waves during the rough weather. The
outer beach extends from middle beach to the outer limits of beach proper. It is washed by waves during
storms or during times of highest water levels.
2.Sandy Beach (Psammolittoral)
This is divided into three categories, they are as follows :
i. Hydropsammon : Submerged sandy bottom
ii. Hygropsammon : Zone immediately landward from water, edge – always saturatd with water roughly
corresponds to the inner beach.
iii. Eupsammon : Zone above hygropsammon – corresponds to middle beach.
Benthic Communities of Inland waters
The benthos of inland waters are vast assemblage of flora and fauna. However, it must be remarked that, “no
vertebrates are represented as true Benthos”. The benthic organisms may be classified as follows :
i) Based on size
a) Macrobenthos (more than 0-5 mm) eg. Crab, insects and their larvae, other crustaceans, molluscs such as
gastropods, polychaete worms.
b) Meiobenthos (Size 0.1 – 0.5 mm) eg. Ciliates, annelids, copepods
c) Microbenthos (size smaller than 0.1 mm) eg. Bacteria, flagellates, ciliates.
ii) Based on mode of nutrients
a)Phytobenthos : Autotrophic life, include varieties of algae, flowering plants and other angiosperms, sea
grasses etc.
b)Zoobenthos : Heterotrophic life, range from microscopic to macroscopic organisms.
iii) Based on mode of life and area of dwelling
a)Epibenthos : Live on top of the substratum regardless of whether the bottom sediment is soft or hard rock.
eg. benthic molluscs, crabs, prawn, macrophtes, worms, micro algae.
b)Endobenthos : Live within the substratum regardless of its type. Interstitial fauna may be included under
endobenthos, mainly borers and burrowers.
iv)Based on Mobility
a)Sessile : They do not possess any form of mobility but remain attached to the substrate.
eg. Fresh water sponges, macro phytic and microvegetation
b)Vagrant : They possess locomotive powers and can move either rapidly or slowly eg. shelled macro –
invertebrates, worms etc.
v) Based on ooze film
a) Ooze film assemblage : Ooze forming / secreting organisms.
b) Associated ooze film assemblage : organisms associated with ooze film.
Periphyton
Periphyton are a miscellaneous assemblage of organisms growing upon free surfaces of objects submerged in
water frequently appearing as a brownish green slimy, slippery layer. It commonly found on plants, wood,
stones and various other objects. It seems to develop in littoral and sub-littoral regions. Periphyton may not
always be regarded as true benthos as they tend to grow on any solid support and likely to contain plankton
and benthic organisms
Distribution of benthos
Qualitative distribution

51
At different bottom conditions and exposure to wave action diversify the littoral zone and makes differences
in fauna and supports different kinds if animals.
- Depth and quality related distribution
- Decreasing diversity and numbers with increase in depth
- Mostly of uniform distribution
The following animation shows the qualitative depth relations of two American lakes
The littoral and sub-littoral populations, insects and molluscs comprise as much as 70% of total number of
different components. Increasing depths beyond the littoral zone, the number of benthic organisms may
diminish namely Bryozoans, Platyhelminthes, Snails, Bivalves, Nematodes, Annelids, insects etc. especially
at first 18 m depth. There is no constancy of composition of different types of lakes because lakes do not have
profundal benthic animal population. Even within a single lake n different composition of population occur at
different places.
The nature of the bottom has selective influence upon the quality of the fauna. Baker (1981) classified bottom
materials in the littoral zone of lake Oneida into 6 different types namely mud, sand, clay, gravel, boulders
and sandy clay. Microfauna exists in the bottom deposits is also established and hence microorganisms are
considered as bottom dwellers and appear as :
1) free swimming or
2) free swimming only in some stage of life cycle or
3) always spend most of time on the bottom materials
Bigelow (1928) divided littoral benthic microorganisms of lake Nipigon, Canada into two ecological groups :
i) the ooze-film assemblage and
ii) the associated ooze–film assemblage
The former group comprises those microorganisms living in and on that film of ooze at upper surface of the
lake bottom contain certain algae, including diatoms, protozoa, rotifers and cladocerans, while the latter
directly dependent upon the ooze film and swim very close to it eg, Cladocerans and rotifers .
9.2. Quantitative and Qualitative movements, seasonal changes and migrations ofbenthos
Quantitative distribution
In shallow lakes, the entire bottom is uniformly productive. The growth of bottom dwellers, whose quantity of produce
at different depths especially in shallow lake, is not same.
The deeper inland lakes can be divided in to 2 groups 1) Those which do not develop chemical stratification during
summer and 2) Those which become chemically stratified and remain so throughout the summer period.
In non-stratified deeper lakes, the benthic forms extend much deeper into the basin resulting in greater mass production.
However,in stratified deeper lakes during summer, the bottom region exposed to hypolimnic conditions lead to less
production quantitatively than the regions above them.
Movements and migration ofbenthos
Under certain circumstances,the benthos exhibits movements within or on the bottom. Certain other organisms move up
and down in streams. Moffett (1943) observed movements of bottom organisms on large wave swept shoal and found
some changes in space due to bottom shifting.
Moon (1935) found that :
(a) the littoral fauna in lake Windermere is in a continual state of movements
(b) this fauna is sensitive to changes is surface level of the lake
(c) more active elements of the fauna move quickly into the inundate portions of the beach and
(d) a rise in surface level only 2.5cm is sufficient to produce a movement of the fauna.
Seasonal changes in benthos
Little is known about the seasonal changes in benthic organisms. In very shallow lakes, the seasonal changes in the
whole benthic region are essentially the same as those which prevail in the littoral zone of deeper lakes. In the abyssal
regions of deeper lakes which never overturn and hence the benthic conditions remain same throughout the year.
Benthos are known to show different morphological changes with respect to different seasons (spring, summer, autumn
and winter) at different zones (littoral, sub-littoral and profundal). In some lakes, the organisms may compose the
overwhelming bulk of entire population and significant fact that each profundal species manifests similar and

52
corresponding seasonalincrease and decrease magnitudes, which are characteristics of the species.
Origin and permanence ofprofoundal bottom fauna
The preformed bottom fauna occurs in inland lakes is composed of forms which occur in neither peculiar nor restricted
to the profundal region, they seem to occupy also the sub-littoral and some extent the littoral zones. The bottom fauna is
not qualitatively unique but is composed of representative of a few species belonging to larger littoral and sub-littoral
population. During spring and fall overturns, these population spread down the lake bottom into the profundal region
bringing into not only the grater numbers of individuals but certain additional species characteristics. However,the
gradual development of stagnation at the bottom bring about a condition which some of the species cannot under go.
Occasionally in unusually deep lakes, certain animals occur which never come to shallow depth (above 50m). Hence,it
appears that profundal bottom forms are not truly a permanent profundal fauna but may themselves be eliminated
completely or party by exposing to stagnation.
Vertical distribution of profundal bottom fauna
Evidently it has been assumed that the profundal bottom fauna largely confined to the uppermost layer of the bottom
deposits. Information secured by Lenz (1931) who by using constructed bottom sampler was able to bring virtually
undisturbed, vertical samples of bottom deposits to the surface and then isolating and examining horizontal strata in
their unaltered relations. Various horizontal levels have been studied down to a depth of 24cm. The largest part of the
fauna occurred in the upper half of the sampler. Some difference appeared in the vertical distribution of various
organisms for eg, Tubificidae concentrated in the upper position, while Chironomus were distributed from the surface of
the mud to a depth of 20cm or more. Moore (1939) indicated and noted that there was an obvious similarity in the
vertical distribution of micro and macro benthos.
Biological productivity
10.1 Circulation of food material, classification of lakes based on productivity
Circulation of food materials
Essential food stuffs in a lake undergo continuous, more or less definite cycles. Natural water body is
completely closed community since there are various direct and indirect influences exerted from outside. In
considering the circulation of food materials in a typical lake, the following fundamental facts must be kept in
mind.
1)The ultimate basic substances are
a) inorganic nutritive materials dissolved in water and
b) certain energies and gases from the atmosphere
2)Chlorophyll bearing plankton and flora and certain bacteria can utilize directly basic materials in
constructing living mater
3)Other organisms, plants or animals are of a dependent superstructure
4)Every organisms of a lake population may
(a) by death and disintegration contributes directly to the dissolved materials and detritus or
(b) be consumed as food by other organisms.
Circulation of food materials
Two general set of processes are construction process and reduction process. Building upward from the simple
food material into the higher is a construction process. Reduction through bacterial action into simple
substances is a reduction process. Cycles are so interrelated that materials may be built up to the same level in
different ways. One cycle through which animals are freed from dependence upon photosynthetic plants ie
from basic dissolved nutritive materials through bacteria which change CO2 to organic carbon in the absence
of sunlight to certain animals which consuming them.

53
Classification oflakes on the basis ofproductivity
Many attempts have been made to classify lakes on limnological bases,related in some way or another to productivity
during the past five decades. The combined contributions of a number of those attempts have been lead to the
classification of lakes into three major types viz,
1. Oligotrophic lakes
2. Eutrophic lakes and
3. Dystrophic lakes
10.2. Laws ofminimum, biotic potential and environmental resistance,quantitative relations in a standing crop
Law of the minimum
Existence and production of animal and plant life depend upon the proper quantitative and qualitative composition of
the environment for each component organisms. Liebig’s law of the minimum originally applied to plants and is stated
as each organism required a certain number of food materials and each of these materials must be present in a certain
quantity. If one of these food substances is absent or present in minimal quantity the growth will be minimal. The yield
of a plant or animal according to this law is determined by the quantity of that particular substance present in minimal
amount as per the demands of the organism.
The law of minimum has had a wide acceptance. Liebig’s law of the minimum is the foundation of law of limiting
factors which is dependent on one factor upon another. Various environmental factors acted independently wherein if
one factor in present in limiting quantity and increase of other factors would effect no change.
Biotic potential and environmental resistance
The biological productivity of any body of water or any portion of that body of water is the end result of the interaction
of organism present with the surrounding environment. Biotic potential is the characteristics and abilities inherent within
an organism which enable it to exist and reproduce. It is the sum total of all of those capacities of an organism which
determine its relative success in solving all problems of maintenance. It is a sum of the number of young produced at
each production.
Every environment contains active features which work toward the control of production in various organisms involved.
Thus the environment resists to a greater or less extent for the fulfillment of biotic potential. In the long run, nature acts
toward a balance between these two tendencies in which each organism maintains itself in a suitable environment
without overpopulation.
The principles of biotic potential and the
environmental resistance together with all of their
associated features are just a pertinent in aquatic biology as in terrestrial situations. Biological productivity of any

54
aquatic community is a general measure of all of adjustments between biotic potential and environmental resistance
existing within it.
Quantitative relationships in a standing crop
Any body of water maintains a certain standing crop of organisms composed primarily of 5 large groups viz,
phytoplankton, bottom flora, zooplankton and fishes. This series composes a nutritional chain in which the first two
constitute a producing class and the other three are the consumers. Therefore these organisms are an expression of the
productivity of water concerned.
The actual values expressed into this pyramid of aquatic life are different to some extent in different lakes but some
form of pyramid is the rule. This figure illustrate the dissolved organic matter composes approximately 60% of total
diagram, the fish only one-half of 1% and the other animals slightly more than 5%.
10.3. Laws ofminimum, biotic potential and environmental resistance,quantitative relations in a standing crop
Trophic dynamic
In the trophical dynamics of an ecological system, basic processes are in the nature of transfers of energy. The ultimate
source of such energy is solar radiation. Earlier work have raised the biological conclusions which seem to have a
certain validity like :
a. food cycles rarely have more than five trophic levels
b. separation of an organism from basic source of energy (solar radiation) lead to less chance of dependence upon
trophic level for energy
c. the consumers seem to be progressively more efficient in the utilization of food supply
d. productivity and photosynthesis increase from oligotrophy to eutrophy and then
decline in lake.
Successional phenomena
All environments are dynamic and undergo changes is the fundamental principle of
ecology. These fundamental changes more or less predictable alternations involving
expanses of time and these changes may be due to :
a) the action of predominating inorganic factors in the environment eg, erosion
b) the action of organisms in modifying the environment or
c) the combination of (a) and (b)
One fact common to all situations exists that the various components of the biota must meet the changing conditions in
one of the following ways, such as :
a) adaptation
b) migration and
c) extinction
Ecological successions of various kinds go on in lakes and other inland waters as certainly as they do on land. The
movement of the units of lentic series is in the direction of extinction by filling of basins and in the lotic series it is in
the direction extension of stream length and a cutting of stream bed to base level.
Eutrophication
In general and within limits, the productivity increases with the age of a lake. Storm (1928) has stated the process as
follows:
The natural process of the maturing of a lake is that of eutrophication. The original state of all lakes must be assumed to
be oligotrophic but later due to surplus organic sediment occurring from life process of a lake is changed to eutrophic
condition. The quantities of plankton, oxygen curves and average depths are the first features to be changed and later the

55
bottom fauna.
It must be clearly understood that the maturing process takes place at very different rates in different lakes. For example,
in northern United States,majority of lakes basin formed during glacial period but they have matured at different rates
and many small basins have long ago passed the succession stages into old age and are become dry land. If the lake is
smaller, a rapid eutrophication and further extinction take place but certain other lakes fail to go through the usual
evolution from oligotrophy to eutrophy even though natural filling may render the hypolimnion smaller than the
epilimnion.
Dystrophication
The dystrophic lake basins during their initial stages are low productive (essentially oligotrophic). These primitive
basins varied greatly in size and depth covering considerable areas having hypolimnion exceeding the epilimnion.
During certain circumstances an incomplete decay of plants and accumulation of humic materials appear the beginning
of dystrophication. After the initiation of dystrophy, the succession progressed by marginal plant encroachment or by
bottom accumulations in incompletely decayed plant materials or by both and passing through the stages into a peat bog.
Indices ofproductivity in lakes
Limnologists have looked for indices of general biological productivity in lakes. There are two considerations involved
and must be kept clearly distinguished, they are (a) the inherent capacity of a lake to support life (biotic potential) and
(b) the actual productivity at a given time. Obviously one or two indices of productivity would give a dependable
evaluation.
1.Average depth : The average depth of a lake is the determining factor for productivity. The dissolved oxygen content
of various layers of a lake is the indicator of richness in nutritive substances especially at a depth up to 10 m stratum.
The dissolved oxygen content is greater in oligotrophic lakes than that of epilimnion. Certain other features mainly the
degree of development of littoral regions constitutes important influences in determining the production of the lake.
2.Rooted submerged vegetation : Kluge (1926) claimed that the amount of rooted, submerged vegetation may be an
index of lake productivity. It is a well known fact that the amount of rooted submerged vegetation is governed by a
number of factors such as degree of exposure and slope of the submerged shelf. Large lakes for example, lake Nipigon
may maintain a great fish production which could be predicted from the scanty vegetation, whereas the small lakes
having submerged vegetation does not show productivity.
3.Plankton : Plankton is an index of generalproduction. Eutropic lakes are characterized by quantitatively rich in
plankton, while oligotrophic lakes have a plankton poor in quantity. It has been claimed that abundance of plankton is
associated with rich bottom fauna and paucity of plankton accompanies a poor bottom fauna.
4.Bottom fauna : European workers have stressed the quality of the bottom fauna at deeper water as an indication of the
productive character of a lake. Form of basin, character of bottom deposits, water movements etc. would be a true index
of the general richness of a lake. When a rich benthic fauna is present a high total productivity is common.
5.Organic content of water:The standing crop of dissolved organic matter is much greater than the total organic matter
in the plankton supported by the same water. The dissolved organic matter is said to be constant in quantity and
composition that the character of a lake may be judged. It has been shown that a constant relation exist between the
plankton and the total organic matter in the water. The presence of organic content has become a new subject to predict
the generalindex of productivity.
6.Chlorophyll content : Chlorophyll content is used as an index of the photosynthetic capacity. This measurement can be
used as a convenient method for evaluating biological productivity.
7.Other indices : The organic content of bottom deposits is important as food for benthic organisms. In general hard
water lakes are not highly productive. The total alkalinity and total phosphorous appear to be the most valuable indices
of productivity.
Artificial enrichment
The waste products of human beings and industries often find their way into natural waters and produce contaminations.
Removal of forests and tilling of land bring changes through the medium of drainage but are not the nature of
contaminations. The enrichment of water is due to the addition of substances and subsequent changes increase the
amounts of essential nutritive materials. Among the contaminations, most likely are the domestic sewages downwash

56
from manured fields and other organic matter.
The enrichment effects due to contamination are more to be expected in the smaller lakes than larger ones. Evidences
have shown that the sewage from large cites brought into the larger lakes enters farther into the open lakes and dilutions
becomes greater leading to enrichment having distinctly increased biota.
Sometimes and also at present use of fertilizers have favoured the fish production in the water bodies. Repeated
application of artificial fertilizer to natural waters are dangerous leading to winter kill of fish in the northern United
States lakes. Increasing production in enclosed waters such as ponds, small lakes and reservoirs is more prominent
compared to large natural bodies and water
Lotic environments
11.1 Running waters in general
Running waters
Investigation on running water series is less compared to that of lakes. A comprehensive and prolonged study
has been made in America on Illinois river over a period of 50 years. The lotic environments differ from lakes
and similar waters in the following respect :
1)Depth – As a rule, the depths of running water units are small compared to lakes
2)Width of basin - Apart from the channel expansions (sometimes designated as river lakes), the water is
confined to relatively narrow channel.
3)Current - Whole volume of water flows in one direction.
4)Condition of gradient from source to month - All conditions such as physical, chemical and biological
gradually change with distance along the main channel in a definite direction.
5)Extension of channel with age - Stream systems usually increases their length, width and depth with
increasing age.
6)Permanent removal of eroded and transported materials - At any position during the course of running
water unit, materials eroded are transported downstream.
7)Absence of prolonged stagnation - Constant flow and mixing of water usually eliminates prolonged
summer stagnation of the bottom waters.
8)Relative influence of physical factors - Physical factors of the environment are relatively more important
then in lentic waters.
9)Basic food materials - Streams manufacture within themselves the basic food materials but much depends
upon the contribution from surrounding land areas.
Physical and Chemical conditions of Lotic environments
1)Water movement
Current in one direction is the outstanding feature of lotic environments. Current is the greatest velocity which
interfere during water falls and finds minimum where long distances of slope of channel becomes negligible
during which the channel approaches base level. Some streams are slow and sluggish throughout their length
and other swift throughout their whole course. The distribution of velocities in streams is determined by
different factors such as shape of channel, roughness of channel, size of channel and slope channel. The
maximum velocity is usually found somewhere within the first one third of the depth of water. The velocity
pattern of a stream altered by strong winds which blowing either sometimes upstream or predominantly
downstream. Ice cover reduces the surface velocity because of the greater retarding effect of ice as compared
with air. The current rate may vary markedly at positions on the front, top, sides and rear side of submerged
stones likewise the same is true of the gaps, channels and interstices between stones and similar objects.
Erosion, transportation and sedimentation are inseparable accompaniments of stream currents. Those materials
which are not carried in suspension are rolled downstreams. The transporting power of the streams varies with
changes in velocity.
2)Temperature
In lotic environments, the temperature phenomena are different from those in lentic situations. The principles
features are :
a) tendency toward a uniform temperature at all depths

57
b)tendency to follow air temperatures more closely
c)thermal stratification usually absent or temporary
The temperature variation is common in stream especially in long stream and slow current situations. Certain
circumstances leading to temperature variations are differences in
a. depth of water
b. current velocity
c. bottom materials
d. temperature of entering of tributary / small stream
e. exposure to direct sunlight
f. degree of shading and
g. time of day
In long stretches of shallow unshaded, slow moving currents, there is gain in temperature during the clear days
of mid summer, but there is different temperature during night.
3)Turbidity
A greatest extreme of turbidity occur in the flowing water series. Streams in mountain and rock beds the
turbidity is minimal while in the plain region the turbidity is high (eg, North American Missouri and Kansas
rivers). In some stream systems, high turbidity is a permanent feature throughout the year. The turbidity in
streams is largely due to silt, detritus and other non-living materials. Since plankton production is commonly
restricted, it usually plays a minor role in turbidity production. Domestic sewage and other forms of stream
pollution commonly increase turbidity.
4)Light
The most important factor in the determination of light punctuation is turbidity and its influence is great in
certain waters which reduce the development of plants. In turbid rivers where light decreases due to presences
of suspended silt in excess of 90% in first 25 mm of water depth.
Chemical conditions
1)Dissolved gases
Due to the involvement of mechanical condition in water current, the dissolved oxygen supply of
uncontaminated streams is high leading to saturation point. Generally oxygen content begins to increase soon
after sunrise, reaches a maximum shortly after mid-day and then declines to a minimum. This variation extend
from considerable supersaturation to a substantial reduction in some instances is due to oxygen production by
green plants during day and consumption by respiration of biota and decay of organic matter during both days
and night. Under some circumstances, some rivers show very distinct diurnal oxygen pulses. The factors
affecting the dissolved oxygen are: character of stream flow, slope of channel, temperature, oxygen released
by chlorophyll bearing plants, oxygen consumed in respiration of the biota and oxygen consumed in the decay
of organic deposits on the bottom.
2)Dissolved solids
The dissolved solids vary greatly depending upon the regional characteristics of the drainage basin. It is
known that in general the lotic water contains more salts and less soluble nitrogen than lentic waters
(Chapman, 1931). The dissolved solid content is often subjected to changes by dilution or addition at stream
junctions. Loads of solids in streams are common and it has been estimated that the range of total solid in the
river systems of Upper Peninsula is 100 to 200 ppm while in Lower Peninsula is 200 to 500 ppm.
3)Hydrogen ion concentration
The general features of pH in lotic environment are not different from that of lentic environments. Currents
tend to keep the pH uniform over considerable distance; it keeps any acidity due to accumulating free carbon
dioxide reduced. However, a uniform pH over considerable distance in lotic environment is kept. So, the
streams would never develop more intense acidities unless they are contaminated or receive heavy seepages
from mineral deposits.

58
11.2 Biological conditions, productivity features of lotic environments, Influence of currents,Plant
growths
Biological conditions
The range of conditions is reflected in the biota which varies from distinctly characteristic organisms to lentic
flora and fauna of the system. The greater the current velocity, the greater will be the divergence of lentic and
lotic populations. The lotic assemblages occupy the upper elevated positions of stream system. Certain groups
of animal exclusively lotic ones such a stone–fly larvae (Plecoptera), black-fly larvae (Simuliidae) etc. are
restricted to running water series. Generally it is said that the lotic populations are more restricted in the
number of species.
Productivity features of lotic environments
The quantitative features of plankton and productivity of the microorganisms are very important in the lotic
series of water bodies. According to Needham (1930), the ecology of the smaller streams especially brooks
and creeks have general features and they are :
1. Distribution of aquatic animals in brooks and creeks are dependent largely upon
a) temperature of the water
b) nature of the bottom
c) velocity of current
2. Smaller streams from the source of mouth have 2 distinct types of habitats such as pools and riffles
3. Riffle bottoms greatly exceed the pool bottom in productivity
4. Fishes in brooks and creeks tend to seek the pools. Pools act as catch basins for animals brought down from
the riffles and these drift animals serve as food for pool fishes.
5. Absences of higher aquatic vegetation leading to productive silt bottom for small organisms
6. Plant beds in smaller streams markedly affect productivity. Stream bottom supporting growths of aquatic
plants were found seven times more productive than stream bottoms bare of vegetation.
7. Small cold, headwater streams less than 7 ft are more productive (twice) than the maximum width.
Influence of current
Lotic fauna is typically composed of animals whose dissolved oxygen demand is fulfilled by the oxygenated
waters of streams. In some forms, the requirement of inherent current demand is more when compared to
oxygen demand in lotic environment. The gill area of May fly nymphs in mountain streams varied inversely
with the dissolved oxygen content, but not close relation with the current rate. Some organisms are more
dependent upon the increased amount of dissolved oxygen and the mineral salts in solution than upon current.
In certain May fly nymphs and caddis – fly larvae from a swift stream, the oxygen consumption is higher than
the closely related , equal sized nymphs and caddis – fly larvae from a pond. The same situation is exit in
aquatic crustaceans (Asellus aquaticus), where swift stream consume more oxygen than that of sluggish
flowing water. Nymphs are less resistance to oxygen deficiency than those in quiet water.
Running water animals seek certain physico-chemical conditions and are compelled to tolerate current as a
mechanical condition against which they struggle. With the exception of the plankton, all other biota have
developed means of maintaining themselves (except during floods) in the streams have adopted to thrive well
and even exist. Among organisms of running waters, the character facilitating to maintain their position is
diversified. Some of the insect larvae build heavier cases in running water than the quiet water.
An accompanying feature of current is molar action. The action and severity of this vary widely with current
velocity, the nature of the bottom materials and other circumstances. Injury and mortality may be very high at
times of flood. In addition to molar action, eroding and scouring action of flood waters often depopulate the
streams, so that restocking is necessary.
Nature has numerous and effective means of restocking populations such as upstream or down stream
migration of animals from adjacent waters, transportation by currents, reproduction by the individuals, spread
of aerial adults from nearby waters and transportation as wind -blown materials. The production of drift
materials in a stream is one of the invariable effects of the current, even in the absence of floods.
A phenomenon arising out of current action is the depositions of eroded silt. In some lotic conditions, e.g.
Instep, rock bed streams such deposits are absent. Certain organisms regularly occupy regions of silt deposit
with no detrimental effects. Some of the organisms possess certain mechanical means of avoiding suffocation
by the mud. Another influence of current is the elimination of surface breathers except in the very slow

59
moving regions.
Plant growth
The larger aquatic plants do not occur in stream except where the current is greatly reduced. Occasionally,
certain rooted plants (Chara and others) may be found in rapid streams. There is distinct tendency to dwarfing
in plants that grow in mountain streams. Certain water mosses are found in rapid current, especially in streams
not subject to severe floods. Sometimes, it is also important to note that slow moving sluggish streams become
plant choked maintaining flora composed of submerged and floating types of plants. In the slower water of
stream edges, a narrow margin of aquatic plants occur but with limited success. The plants provide benefits in
fish production owing to supply shelter, protection for young ones, abundance of food; aquatic invertebrates
which are sometimes become food for fishes.
Algae of swift streams possess the holdfast cells or other structures to support over any substratum and to
remain there against the strong current. The fresh water red algae, Lamanea is found only in rapid waterfalls.
Green algae, Cladophora, attaches to stones and other supports in slow streams. Certain other algae which lack
holdfasts resist current action because of abundant mucous secretion.
11.3 Nekton, benthos, Temporary and head water streams,general ecological succession
Nekton – benthos characteristics
Since streams are shallow water bodies and hence they do not support organisms inhabiting at the bottom but very rarely
the deep waters of rivers support such organisms. In most of the streams a sharp dividing line between nekton and
benthos on natural basis does not exist. Of the vast communities of organisms involved, fishes are the only group which
might be called nektonic. The benthos and nekton have been jointly grouped to have abundant quantities in shallow
moving water bodies.
Temporary and head water streams
During dry seasons, the channels are either completely devoid of water or at most contain few isolated pools. Such
water may not support life but really and especially during certain season certain assemblages of organisms are present
which possess the following features :
1. Life histories requiring water only in a portion of the cycle and therefore such streams do not support aquatic
residents.
2. No development of higher aquatic plants but few plant eaters available among the fauna.
3. Very rarely found carnivorous who feed upon detritus and microorganisms.
4. Positive rheotropism in some of the motile forms: cling or attach to the substrates.
5. Some of the tolerant species may carry over in pools from one flowing water system to the other.
6. Linear sequence distribution of fishes. With the onset of drought, some fishes move downstream, with rise of water
level, they move towards upstream but maintaining their general distribution.
7. Aquatic insects form the most diversified group of the fauna
The two large types of stream communities are a) those characteristics of swift waters with hard, stable bottom and b)
those characteristics of slow moving waters with soft, unstable bottoms. In swift water type, there is no pelagic
community. The sluggish water type depends upon soft bottom and slow current, decaying organic matter,accumulated
on bottom, support large quantities of bacteria,motile pelagic communities and remain in no fixed position in relation to
bottom.
General ecological succession
It is a known physiographic fact that the head water region of running water unit / system will migrate. Streams for
example extend their growth and proceeds by continually cutting back at their back (source). As the time goes on, the
young stream condition migrate upstream with the migration of head waters and older set of environmental conditions
move upstream to occupy the level occupied by young stream environment.
The migration of stream dependent largely upon the rate of erosion and transportation of materials at the source and is a
slow process. An interesting development in the subject of succession of stream communities as pointed out by Shelford
and Eddy (1929) that permanent stream communities exist, undergo successional development, reach and maintain a
quasi–stable condition and manifest seasonal and annual differences as do terrestrial and marine communities.

60
1. Morphometry oflakes, ponds and streams
Morphometry is the measurement of external form or shape of a selected water body. It is that branch of limnology
which deals with the measurement of significant morphological features of any basin and its included water mass is
known as morphometry. Morphometry defines a physical dimension and involves the quantification and measurement of
any basin. These dimensions influence the water quality and productivity levels.
Morphological features,age and geology of the lake basin along with the level of human interference have a direct and
significant bearing on the structural and functional attributes of the aquatic habitats. Therefore,before undertaking any
limnological investigation it is essential to prepare the maps and generate information on the morphometry and general
characteristics of the area.
A. Morphometry oflakes
a. Location : Trace the correct name of the locality and its latitude, longitude and altitude from authentic sources such as
government records and publications, maps and topo-sheets of the Survey of India etc.
b. History : It is important to know the history of the area,land use of surroundings, formations or excavation of the
basin, past glaciations or tectonic activities if any and other relevant information available from published or
unpublished work, district gazetteer and by interviewing the local inhabitants.
c. Area : Surface area is an extremely important dimension for it is at the surface that the solar energy enters into the
lake and marks the beginning of the lacustrine energy exchanges. As a result many limnological data related to
productivity and heat budget etc. are generally given as unit area of the lake surface,making it possible to compare
meaningfully the limnological characteristic of different sized water bodies.
Requirements: Stakes, measuring tape,graph paper,planimeter
Method
i. Mark a base line AB of suitable length on one side of the water body and plot it on a graph choosing a suitable scale.
ii. Depending on the shape of the water stretch,take two or more such base
lines at right angles to each other.
iii. Put
stakes
along the
shore line at
suitable
distances.
iv. Measure
the vertical
distances
between the baseline and stakes on the shore line at regular or suitable
intervals and note them against the point number 1, 2 and 3 and so on.
v. On the graph sheet plot the vertical distances in accordance with the scale.
vi. Connect all points to form a shore line diagram.
vii. Compute the area directly from the graph or with the help of a planimeter.

61
The method is convenient only for small water bodies but for larger water bodies more sophisticated survey
techniques should be used.
Bathymetric map (Contour map). It can be prepared by recording the depth at several points at equidistance
in the lake; the number of points will depend on the size of the size of the water body. The shoreline map is a
pre-requisite for this exercise and the observer should know the cross-wire bearing in the lake at a given point.
This method is convenient for shallow lakes only.
a. Maximum Length (L): It is distance between two most distant points on the surface of the lake without land
interruptions.
b. Depth (Z): Depth is the minimum vertical distance between the surface and the underlying bottom of the
lake at any point, along with the area it gives an idea of the volume of water in the lakes.
Requirement : Heavy metallic plate (circular) with a central hook (Secchi disc can be used), good quality
nylon rope and measuring tape.
- Tie one end of the graduated rope to the central hook of the metallic plate
- Lower the plate in water till it reaches the bottom
- Measure the length of the rope in water with the help of the measuring tape and the marking on the rope
Result : Express the depth in meters (m).
c. Maximum Depth (Zm): It is the measured at the deepest point of the lake.
d. Volume (V): Volume of the basin is the integral of the areas at successive close depth starting from the lake
surface to the deepest point. It can be computed by the summation of the volume (m3) of truncated cones of
the entire column, (V=∑v). The volume of each stratum is calculated as under:
Where, h = Vertical depth of the stratum
A1 = Area of upper surface of the stratum
A2 = Area of lower surface of the stratum
(The area of the upper and lower surfaces of the stratum can be calculated from the contour map).
e. Mean depth (Z): Mean depth is calculated by dividing the volume of the lake by its surface area (Z/A).
f. Geology: This includes the geomorphological, pedological (origin and development of soil), edaphological
(soil characters) and topographical information, which can be collected from reliable sources like local and
regional offices of survey of India, Geological survey of India, District Gazetteer and relevant published
Literature. In case, no such information is available the help of a Geologist should be taken.
g. Catchment area: It is the surrounding area of the lake which influences it either directly or indirectly
through run off or otherwise. Information regarding the catchment area includes its geology, drainage pattern,
agricultural and other land uses; industrial and sociological aspects; the extent of forest and other natural
resources, and water use pattern etc. Information on the above can usually be collected from appropriate
government authorities or the concerned University departments.
B. Morphometry of ponds
A farm complex comprises of different types of ponds namely nursery ponds, rearing ponds, production ponds
and breeding ponds in aquaculture system. The number and size of these ponds depend upon the water
resources, variety, size of fish to be cultured and type of management.
A viable fish culture practice primarily depends on the selection of a suitable pond size, which in turn depends
upon water retention capacity of the soil and availability of adequate water supply during the culture period.

62
Knowledge of the construction of different types of fish ponds is a pre-requisite for a profitable fish culture.
Areas of silt and clay which retain water to a greater extent are preferred for the construction of fish ponds.
Fish pond soil should have a pH of 7-9. It is always better to determine the nature of soil up to 1.5m depth.
Structures of fish ponds
A typical earthen pond will have the following structures, namely bunds or dikes, harvesting pit, inlet, outlet
and core trench.
Bunds
Bunds are the protecting structures of fish ponds and are very essential. They may be of three types
a) Main bund or peripheral bund – essential for larger fish farms enclosing a number of fish ponds of varied
sizes.
b) Bunds holding water on one side, and
c) Bunds dividing two adjacent ponds.
Slope
The life span and strength of any bund depend not only on the quality of soil but also
on its slope and crown. The slope may be defined as “the ratio of horizontal increase in
the base of the bund from the point of perpendicular to the top edge of the bund to the
edge of the base of the bund on the same side per unit length”. For ordinary ponds of
less than 0.5 ha, the wet side slope may be 1:1.5 and the dry side slope 1:1.
Berm
If the production pond is more than 0.5ha, a platform – like space between bund and
watery area known as berm or bench line should be made available. The width of the
berm may vary between 0.5 and 1.0m, depending on the height of the bund and size of
the pond. The berm apart from serving as a walkable space also protects the bund from
direct contact with water.
Inlet and outlet
These are required especially for larger ponds, in order to ensure a smooth water supply and drainage. Further,
they are helpful in preventing the entry of wild fish from outside and escape of the fish from inside the pond.
The size and shape of these structures largely depend on the area and water spread of the ponds.
Crown
The crown width also depends upon the height of the bund. However, a minimum of 1m crown width is
invariably needed for any bund.
Other measures to be considered during the construction of a fish farm
1. A sedimentation pond or a filtration system is made as a wall with layers of gravel, sand and mud in order
to filter the water, if turbid, before its entry into fish ponds.
2. Nursery ponds may be constructed using brick and cement above ground level in order to reduce mortality
of fish fry.
3. If areas of water scarcity and seepage are to be utilized for fish culture, cement ponds have to be
constructed there.
4. Turfing or stone pitching may be adopted to avoid the sliding of earthen bunds.
It is also advisable to keep fencing around the fish farm to keep the cattle off ponds.
C. Morphometry of Stream
Only narrow and shallow streams can be surveyed by this method. Measure a 50 m or more stretch of the
stream to be mapped. Mark at each interval of one meter and also mark a line called base line, thereafter on
the graph paper representing the points on a sustainable scale. Measure the distance from each point to the
near boundary of the stream by joining the points and the map of stream can be constructed. (Fig 1 & 2)

63
The profile of any section of a stream can be prepared by recording the depth across the stream at small intervals
prepare a graph between the distance and depth to obtain the profile.
Stream morphometry is the measurement of physical dimensions of a (fluvial) object. This is done in the similar manner
of taking measurements with a tool and is applied them to define a dimension. So, quite often the use of stream
morphometry is to get an accurate representation morphology, but more importantly, an accurate characterization of
stream morphology.
Velocity (m/sec) : Rate of movement
Water in a stream moves fastest near the surface and slows down near the bottom,
where the flow is slower by friction from the roughness of the bed material. To
compute the discharge of a stream, we need to compute velocity, which changes with depth. To make the best
estimate of a stream's velocity hydrologists use the average velocity of a stream.
Quick stream flow measuring is best done with a meter to measure water current velocity. Stream flow
measuring is easily accomplished using a water current meter and a tape measure. The current velocity meter
allows to measure stream flow velocity in feet or meters per second and measure water depth in hundredths of
a foot up to three feet. The average stream flow velocity times the cross-sectional area of the stream
determines the stream flow measurement in cubic feet or meters
per second. The area for a channel is known for pipes, or is
determined for a stream flow measurement by measuring the
distance from shore and water depth at various points across the
stream flow to construct a channel profile.
The water current meter offers two unique methods for
determining average water velocity:
1) For small stream flows and pipes, the current velocity meter
may be moved smoothly and uniformly throughout the stream
flow profile until a steady average reading is displayed. This
steady reading is the true average velocity for the stream flow.
2) For larger streams, the current velocity meter may be used to

64
measure a vertical profile of water velocity at several points across a stream channel. The stream flow
measurement for the profile is the sum of the average velocity of each subsection of stream flow times its
cross-sectional area.
Gradient (m/km or %) : drop in elevation over a distance
Stream gradient is the ratio of drop in a stream per unit distance, usually expressed as feet per mile or meters
per kilometer. A high gradient indicates a steep slope and rapid flow of water (ie. more ability to erode);
whereas a low gradient indicates a nearly level stream bed and sluggishly moving water, that may be able to
carry only small amounts of very fine sediments. High gradient streams tend to have steep, narrow V-shaped
valleys, and are referred to as young streams. Low gradient streams have wider and less rugged valleys, with a
tendency for the stream to meander. These are older streams, in geological time.
A stream that flows upon a uniformly erodable substrate will tend to have a steep gradient near its source, and
a low gradient nearing zero as it reaches its base level. Of course a uniform substrate would be rare in nature;
hard layers of rock along the way may establish a temporary base level, followed by a high gradient, or even a
waterfall, as softer materials are encountered below the hard layer.
On topographic maps, stream gradient can be easily approximated if the scale of the map and the contour
intervals are known. Contour lines form a V-shape on the map, pointed upstream. By counting the number of
lines that cross a stream bed within a measured distance, and converting this to the actual measurements of the
land surface, will determine the actual gradient. For example, if one measures a scale mile along the stream
length, and counts 3 contour lines crossed on a map with ten-foot contours, the gradient is approximately 30
feet per mile, a fairly steep gradient.
Stream Gradient Calculations
Cross-sectional area (m2) : Area of the stream perpendicular to main flow
The cross-sectional area of the stream is determined by multiplying channel depth by channel width along a
transverse section of the stream. For a hypothetical stream with a rectangular cross-sectional shape (a stream
with a flat bottom and vertical sides) the cross-sectional area (A) is simply the width multiplied by the depth:
A= (W x D)
Discharge (m3/sec) : Rate of water movement - influences:
1) substrate conditions
2) disturbance of biota
Stream discharge is the volume of water passing through a particular cross-section in a unit of time, measured
in cubic meters per second or cubic feet per second. The discharge of a perennially flowing stream is provided
by the influx of groundwater into the channel. This influx provides what is called the ‘base flow’ of the
stream. Water is added to the stream by runoff from the surrounding terrain during storm events.
Discharge (Q) can be expressed as
Q = A x V
where,
A= cross-sectional area
V= velocity
Determination ofphysical characteristics ofinland (lentic and lotic) waters
Physical properties of water in any aquatic system are largely regulated by the existing meteorological conditions and
chemical properties. The effect of physical forces like light and heat is of great limnological significance as they are
solely responsible for many of the phenomena like thermal stratification, chemical stratification, diurnal and seasonal
variations in the number and distribution of plankton, spatial distribution of micro - and macroorganisms. In the light of
above considerations it is essential to record the important physical parameters as much relevant information can be
derived from it.
Lentic systems are diverse, ranging from a small, temporary rainwater pool a few inches deep to Lake. Examples
include ponds, basin marshes,ditches, reservoirs, seeps, lakes, and vernal / ephemeral pools.

65
Lotic is nothing but the running water series are included all forms of inland waters in which the entire water moves
continuously in a definite direction. Genetically it is stated as brook – creek – river series.
Lotic water bodies (River & Stream)
Lentic water bodies (Lake & Pond)
The most important features which are having practical implications are delineated here.
1. Water surface
Visual changes in the nature of water surface are mainly due to the wind action and to a certain extent are
governed by the topography of the surrounding area. This phenomenon is responsible for the localization and
dispersion of the algal bloom and other particulate organic matter. Therefore, observe the water surface and
record its condition as mirror smooth, rippled, wavy and highly wavy and so on.
2. Water colour
Light coming from the lake surface yields an apparent colour which is the result of the true colour of water
(due to materials in solution), seston (due to living and non-living particulate matter) and the reflections of
surface and sub surface objects. The colour is best judged by observing through a water telescope or also by
the standard empirical colour scale
3. Water temperature
The temperature of surface and subsurface waters can be recorded by drawing water samples with the help of
a sampler (preferably having an inbuilt thermometer) or by dipping the thermoprobe to the desired depth.
Water temperature is measured using a thermometer. Keep the bulb of a thermometer completely immersed in
the surface layers of water for 2-3 minutes until it reaches a constant value. Measure the temperature of the
water while keeping the thermometer in the water.
i. Surface temperature
Measurement of surface water temperature is very important. Any good grade, simple type of mercury
thermometer would serve the purpose. Any common chemical thermometer graduated to 0.2°C can
conveniently be used, but it should be secured well in a metal case to avoid loss in the field. Surface water is
taken in a plastic container and its temperature is recorded immediately by dipping the thermometer for about
one minute or more.
ii. Subsurface temperature
Measurement of temperatures at various depths below the water surface requires specially designed
instruments. Temperature often differs with depth and positions at which temperature is to be measured are
remote from the observer. Subsurface water temperature can be measured by different apparatus and are
delineated below.
a. Thermo-flask sampler method
A thermos flask sampler along with in-built thermometer is lowered in water to desired depth and closed with
the help of cord. Then it is pulled out of water. The temperature is read from the in-built thermometer.
b. Reversing thermometer method
This instrument has a main thermometer which registers the temperature and an ordinary thermometer which
is used for correcting the change brought about by atmospheric temperature. It consists of a conventional bulb
connected to a capillary in which a constriction is placed so that upon reversal the mercury column breaks off
in a reproducible manner. The mercury runs down into a smaller bulb at the other end of the capillary, which
is graduated to read temperature. A 360° turn in a locally widened portion of the capillary serves as a trap to
prevent further addition of mercury if the thermometer is warmed and the mercury expands past the break-off
point. The remote-reading potentialities of reversing thermometers make them particularly suitable for use in
measuring subsurface temperature as a function of pressure. In this application, both protected thermometers
and unprotected thermometers are used, each of which is provided with an auxiliary thermometer. They are

66
generally used in pairs in Nansen reversing water bottles. They are usually read to 0.01°C, and after the proper
corrections have been applied, their readings are considered reliable to 0.02°C.
4. Turbidity
Suspension of particles in water interfering with passage of light is called turbidity. The suspended particles
may be clay, silt, finely divided organic and inorganic matter, plankton and other microscopic organisms. The
following methods are generally used for determining the turbidity of water sample.
a. By Jackson’s candle Turbidity meter (JCT) and
b. Electrical / Electronic turbidity meter commonly called as Naphlometer
a) By Jackson’s candle Turbidity meter (JCT)
It is based on the transmittance of light from a frame of a ‘standard candle’ through the sample column of
certain path length such that the flame becomes indistinguishable against background illuminations. Turbidity
is inversely proportional to the path length. In brief, it is based on comparison of intensity of light scattered by
the sample and a standard reference under comparable conditions. Higher the intensity of scattered light,
higher is the turbidity.
The lowest turbidity which could be measured with JCT is 25 units. As such indirect secondary methods are
required for measuring turbidities in the range of 0-5 units. However, the results obtained with different types
of secondary instrument do not match with one another because of fundamental difference in the optical
systems even though the instrument are all pre-calibrated against JCT. This method is not in much use today
mainly because of difficulties in getting the standard candle.
b) Nephlometric method
Principle : Formalin polymer is the turbidity standard preference suspension for water. It is easy to prepare
and is more reproducible in its light scattering properties. A given concentration of formalin suspension
having 40 NTU has approximately a turbidity of 40 JTU. Therefore, turbidity based on formalin will
approximate units desired from JCT but will not an identical.
Materials : i) Turbidity meter – It consists of a light source for illumination of the sample and one or more
photoelectric detectors with readout device to indicate the intensity of light scattered at 90o incident light. The
sensitivity of the instruments permits detection of turbidity difference of 0.02 NTU or less in water having
turbidity <1.0 NTU. The instrument measures generally from 0-40 NTU. Various ranges are necessary to
obtain both adequate coverage and sensitivity. However, meters having wider ranges are also available today.
ii) Sampler tube – Clear colourless glass scrupulously cleaned both inside and outside without scratch the tube
be sufficiently long so that they are not required to be touched where light strikes.
Reagents :
i) Turbidity free water – It is obtained by passing distilled water through membrane filter having pore size <
100 mm. If filtration does not reduce turbidity, distilled water itself is used.
ii) Stock turbidity suspension
a) Solution I – It is prepared by dissolving 1.0 g of Hydrazine sulphate in distilled water and diluted to 100 ml
in a volumetric flask.
b) Solution II – It is prepared by dissolving in 10.0 g of Hexamethylene Tetramine in distilled water and
diluted to 100 ml volumetric flask.
c) In a 100 ml volumetric flask, 5.0 ml of solution I is mixed with 5.0 ml of solution II. Allowed to stand for
24 hours at 25+3oC. This be diluted to 100 ml mark of the flask and shake properly. Turbidity of this
suspension is 400 NTU.
iii) Standard turbidity suspension – 10 ml of stock suspension be diluted to 100 ml by turbidity free water. The
turbidity of this suspension is defined as 40 NTU. Such suspension is prepared weekly.
Procedure :
i) Turbidity meter calibration – Generally these meters are kept calibrated by the manufacturers. Further,
manufacturers operation manual could be useful in calibration if required.
ii) Measurement of turbidity of < 40 NTU – The sample is thoroughly shaken. The air bubbles are allowed to

67
escape. The sample is poured into the turbidity meter tube and the turbidity is read directly from the scale or
from the calibration curve.
iii) Measurement of turbidity of . 40 NTU – The sample is diluted with turbidity-free water until its turbidity
falls between 30.0 and 40.0 NTU. Now the turbidity of the original sample is computed from the turbidity of
the diluted sample and dilution factor. The stock turbidity suspension of 400 NTU be used for continuous
monitoring. High turbidities determined by direct measurement are likely to differ appreciably from those
determined by dilution technique.
Calculation :
NTU = A (B+C)/C
Where, A = NTU found in the diluted sample
B = Volume of dilution water
C = Sample volume taken for dilution.
Interpretation of Result :
The turbidity readings be reported as follows
5. Transparency
The turbidity of water is directly related to light penetration and visibility or transparency which can be measured by
Secchi disc. This disc was devised by an Italian scientist, Secchi
(1865) for studying the transparency of aquatic bodies. The Secchi
disc is a metallic plate of 20 cm diameter with four (alternate black
and white) quadrants on the upper surface and a hook in the centre
to tie a graduated rope.
Principle : The transparency is inversely proportional to the turbidity
of water,which in turn is directly proportional to the amount of
suspended organic and inorganic matters. When the disc is gradually
lowered in water it remains visible in the euphotic zone, only to that
lower level where light is about 15% of the radiation at the surface.
Requirement : Secchi disc, measuring tape, graduated nylon rope etc.
Method :
a. Lower the disc in water and note the depth (in cm) at which it disappeared
b. Now slowly raise the disc upward and note the depth at which it reappears
c. Take the average value of Secchi disc depth (SDD) or transparency
Calculations : Calculate the euphotic limit and vertical attenuation coefficient as follows
Euphotic limit (cm) = 2.5 x SDD
Vertical attenuation coefficient (Extinction coefficient) = 1.7/SDD
Determination of chemical characteristics of inland (lentic and lotic) waters
Chemically, pure water does not exist on the earth but the natural waters differ in their chemical content. As
discussed under physical characteristics of inland waters, the chemical properties are also equally important
because the existence and continuance of life in water depend upon the presence of substances which natural
water contains, thereby greater the biological productivity. Therefore it is concerned in a way not only with
the water itself but also with its large and varied chemical content. Hence, the most important chemical
characteristics of inland waters are considered here for their analyses as per the standard methods.
1. Determination of pH
It is the measure of the relative acidity or alkalinity and represents the negative logarithm of the concentration
of free hydrogen ions in a solution. The ‘p’ of pH denotes the power of hydrogen ion activity in mole per litre.
pH = log10 [H+] = log10 1/H+

68
Neutral
|______Acid_______|______Alkaline_______|
0 7 14
For convenience, only the logarithm of the number of hydrogen ions is used. pH scale ranges from0 to 14 with
7 as neutral point, below and above which it is acidic or alkaline respectively. In natural waters, the pH
extremes and may reach 3 and 12. Most of the Indian lakes show pH normally between 6 and 9. Increase in
pH during day time is largely due to photosynthetic activity, whereas, decrease at night is the result of
catabolic process.
The pH in water is a measure of hydrogen ion concentration present in water. If the pH value is 7 it is
expressed as neutral while pH values below 7 indicates acidity whereas values above 7 indicates the alkalinity
of the water sample. The pH probe measures pH as the activity of hydrogen ions surrounding a thin-walled
glass bulb at its tip. The probe produces a small voltage (about 0.06 volt per pH unit) that is measured and
displayed as pH units by the meter.
Water pH meter
Principle: The basic principle of the electrometric pH measurement is determination of the activity of the
hydrogen ion by potentiometric measurement using a standard hydrogen electrode and a reference electrode.
Apparatus: pH meter consisting of potentiometer, a glass electrode, a reference electrode and a temperature-
compensating device.
Glass electrode: The sensor electrode is bulb of special glass containing a fixed concentration of HCl and a
buffered chloride solution in contact with an internal reference electrode.
Procedure:
• Before use, remove electrode, rinse, and blot, dry with a soft tissue paper.
• Calibrate the instrument with standard buffer solution. [eg, KCl solution of pH 7.0]
• Once the instrument is calibrated remove the electrode from standard solution; rinse, blot and dry.
• Dip the electrode in the sample whose pH has to be measured.
• Stir the sample to ensure homogeneity and to minimize CO2 entrainment.
• Note down the reading (pH) from the pH meter.
2. Determination of Dissolvedoxygen by Winkler’s method
Principle:
Manganous sulphate reacts with the alkali to form white precipitate of Manganese hydroxide which is the
precipitate of O2 and get oxidized to a brown color of higher hydroxide, which on acidification liberate iodine
equivalent to that of O2 fixed. The iodine is titrated against sodium thiosulphate using starch as indicator.
Reagents
a. Manganous sulphate solution : Dissolve 480 g of MnSO4.4H20 or 400 g of MnSO4.2H20 or 363 g of
MnSO4.H20 in 1000 ml distilled water.
b. Alkaline iodide solution : Dissolve 500 g NaOH (or 700 g KOH) and 135 g NaI (or 150 g KI) in 1000 ml
distilled water (or dissolve 100 g KOH and 50 g KI in 200 ml distilled water).
c. Concentrated Sulphuric acid
d. Starch solution : Dissolve 2gm laboratory grade soluble starch and 0.2 g salicylic acid in 100 ml hot
distilled water.
e. Sodium thiosulphate solution (0.025 N): Dissolve 6.203 g of Na2S2O2.5H2O in 1000 ml distilled water.
Procedure :
• Water sample is collected from surface in 125 ml Dissolved Oxygen bottle avoiding formation of bubbles.
• Add 1 ml alkaline iodide and 1 ml MnSO4 into the bottle.
• Mix well and the precipitate formed is allowed to settle for few minutes.
• Add 1 ml of conc. H2SO4 and shake well to dissolve the precipitate.
• Take 50 ml solution in a conical flask.
• Titrate against std. Na2S2O3 using starch as indicator (2-3drops).
• The end point is blue to colorless and titer value is measured.
Calculation

69
A x N x V x 1000 x 22.4
DO (mg/l) = ______________________
B (A-L) x 0.4 x 0.698
Where,
A= Volume of the DO bottle
N= Normality of Na2S2O3
V= Titrate value
B= Volume of sample taken
L= Volume of reagent used
3. Estimation of free Carbon dioxide
Titrimetric method
Principle: Free CO2 reacts with NaOH or Na2CO3 to form Na(HCO3)2, the completion of the reaction is
indicated by the appearance of pink color in the presence of phenolphthalein indicator at pH of 8.3.
Reagents:
a. Stock NaOH solution : Dissolve 4 g NaOH in 1000 ml distilled water.
b. Std. NaOH solution (0.02N) : Dissolve 200 ml of stock solution to 1000 ml with distilled water.
c. Phenolphthalein indicator : Dissolve 0.5 g of phenolphthalein powder in 50ml of 95% C2H2OH and add
50ml distilled water.
Procedure:
• Take 50 ml of sample in a conical flask.
• Add 4 to 5 drops of phenolphthalein indicator
Upon addition of the indicator if the colour changes to pink it indicates absence of CO2 and if no change, then
titrate the sample against standard 0.02 N Sodium hydroxide until the pale pink color develop and remain for
30 sec.
• Note down the burette reading
Calculation :
V x N x 44 x 1000
Free CO2 (mg/l) = _________________
Volume of sample
V = Volume of 0.02N NaOH
N= Normality of NaOH
4. Determination of Alkalinity in water
Titration Method
Principle:
Hydroxide ions present in a sample react with acid at a specific end point pH. Alkalinity is primarily due to
anionic carbonate and bicarbonate. The pH equivalent at the end point of titration is determined by the
concentration of CO2 at that point and it is in turn is regulated by concentration of carbonate. Phenolphthalein
alkalinity is a term generally used for titration at a pH of 8.3 when hydroxide and CO3
- are present the end
point is indicated by disappearance of pink colour. Similarly, methyl orange alkalinity is the alkalinity due to
the presence of CO-
3 and HCO3
- and the sample aquires yellow colour and at the end point of titration changes
to orange red or red at a pH of 4.4.
Reagents :
• Phenolphthalein indicator : Dissolve 0.5 g of phenolphthalein powder in solution of 95% ethyl alcohol and
add to it 50ml distilled water.
• Methyl orange indicator : Dissolve 0.5 g methyl orange in 100 ml distilled water.
• Std. (0.02 N) Sulphuric acid
Procedure :
• Take 100 ml water sample in a 250 ml conical flask.
• Add 3 drops of phenolphthalein indicator.
• If turns pink, titrate with 0.02 N H2SO4 until the pink color just disappears.
• Note down volume of acid used.
• Then add 3 drops of methyl orange indicator to the same water sample.

70
• If the water turns yellow, titrate acid until a faint orange end point is obtained.
• Note the volume of the acid used decreasing this titration.
5. Determination of reactive Phosphate – Phosphorus
Principle :
The method depends on the formation of phosphomolybdate complex and its subsequent reduction to highly
coloured blue compounds. The water sample is allowed to react with a mixed reagent containing molybdic
acid; ascorbic acid and trivalent antimony. The resulting complex heteropolyacid is reduced to give a blue
solution, the extinction of which is measured at 8850 Ao or 885 nm using a spectrophotometer.
Reagents :
• Ammonium molybdate : Dissolve 15g of ammonium molybdate in 500ml of distilled water.
• Sulphuric acid : Add 140 ml of conc. H2SO4 to 900 ml distilled water.
• Ascorbic acid solution : Dissolve 27g of ascorbic acid in 500 ml distilled water.
• Potassium Antimony Tartarate (PAT) : Dissolve 0.34 of PAT in 250ml of distilled water.
• Mixed reagent : To prepare 500 ml of mixed reagent, mix together 100 ml ammonium molybdate, 250ml
H2SO4, 100ml ascorbic acid and 50 ml PAT. Prepare this reagent for use and discard any excess.
Procedure:
• Take 100ml of sample in conical flask.
• Add 10+0.5ml of mixed reagent.
• After 5 min and preferably within 2-3 hrs, measure the extinction of the solution at 885 nm.
Calculation :
µg at. P/l = Extinction x F
Where, F=Factor value
6. Determination of Nitrate - Nitrogen in water
Cadmium reduction method
Principle : Nitrate is the reduced almost quantitatively to nitrite, when a sample is run through a column
containing Cadmium fillings loosely coated with metallic copper. The nitrite thus produced is determined by
diazotizing with sulphanilamide and coupling with NNED [N-(1-naphthyl ethylene diamine dihydrochloride)
to forma highly colored azo dye, the extinction of which is measured at 543 nm. A correction may be made
for any nitrate initially present in the sample. The nitrate in the sample can also be reduced to nitrate by an
overnight reduction method.
Reagents :
• Ammonium chloride solution (concentrated) I : Dissolve 125g of AR quality ammonium chloride in 500 ml
distilled water.
• Ammonium chloride solution II: Dilute 50 ml of conc. Ammonium chloride solution to 200 ml with distilled
water.
• Sulphanilamide solution : Dissolve 5g of sulphanilamide in a mixture of 50 ml of conc. H Cl and about
300ml of distilled water.
• NNED [N-(l-Naphthyl) – ethylene diamine dihydrochloride solution] : Dissolve 0.5g of NNED in 500ml
distilled water.
Procedure :
• Add 1-2 of ammonium chloride to the 50 ml sample in the conical flask and mix it.
• Add the sample to the column and allowed to pass through it.
• Collect 25 ml of the reduced solution in measuring cylinder.
• As soon as possible after reduction, add 0.5 ml sulphanilamide and add 0.5 ml of NNED solution and mix.
• Measure the extinction between 10 min to 2 hrs at 543 nm wave length.
Calculation:
µg at. NO3 –N/l = (E x F) – C
Where,
F = Factor value
C = Concentration of nitrite present in sample (mg at. N02 –N/lt).
7. Estimation of chemical oxygen demand (COD)
The chemical oxygen demand or permanganate value of water is normally estimated by adopting alkaline

71
oxidation with permanganate. Chromic and permanganate in acidic conditions are not suitable for oxidizing
the organic matter present in water, these oxidants are known to oxidize the chloride ions of the water into
free chlorine keeping this in view, the oxidation of organic matter with permanganate in alkaline condition is
preferred for the analysis of COD in water.
Principle
Under alkaline condition, permanganate oxidizes only the organic matter present in water without oxidizing
Cl, Br and I to Cl2, Br2 and I2 respectively when all such organic matter is oxidized permanganate is allowed
to liberate iodine, from potassium iodide under acidic condition. Iodine so liberated is titrated against
thiosulphate using starch as an indicator. By running a blank, the quantity of thiosulphate required to react
with all the iodine liberated by the unreduced permanganate is estimated. From those 2 litre values, the
chemical oxygen demand of the sample is calculated.
Reagents
1. 0.1N potassium permanganate stock solution : 3.16g of KMnO4 is dissolved in a little distilled water and
the volume is made up to 1 litre with distilled water. this solution is stable when kept in a amber, coloured
bottle.
2. 0.01N potassium permanganate working solution : 100ml of the above stock solution is made up to 1lit with
distilled water.
3. 25% sulphuric acid solution : 100ml of concentrated sulphuric acid is carefully mixed with distilled water
and is made up to 400ml.
4. 5% sodium hydroxide solution : 5g of sodium hydroxide is dissolved in 100ml of distilled water.
5. 0.1m potassium iodide solution
16.6g of KI is dissolved in distilled water and the volume is made up to 1 litre with distilled water.
6. 0.02N sodium thiosulphate solution : 4.964g of sodium thiosulphate pentahydrate is dissolved in 1 litre of
distilled water.
7. 1% starch solution (indicator) : 1g of soluble starch is added to 100ml of boiling distilled water. to this
0.5ml of phenol is added as preservative.
Procedure

72
The blank value is estimated by using 100ml of distilled water instead of the water sample. All over the
treatments and chemical analysis of the blank should be carried out as per the procedure – adopted for the
sample.
Calculation :
Chemical oxygen demand or permanganate value is calculated using the formula
COD (mg/l) = 8 x N x 1000 (b – s) / 100 (volume of the sample)
N – Normality of sodium thiosulphate (0.01 N)
b – ml of sodium thiosulphate solution used for titrating the blank
s – ml of sodium thiosulphate solution used for titrating the sample.
Collection and identification ofFreshwater Plankton
Plankton
The term ‘plankton’ was coined by Victor Henson in 1887 to designate the heterogeneous assemblage of suspended
microscopic materials, minute organisms and detritus in water which wander at mercy of winds, currents and tides.
However,the use of the term has been confined to designate only the microscopic, free-floating organisms; which
depending on their nature are divided in two major groups, namely,
phytoplankton and zooplankton.
Based on the size, the plankton have been classified as ultra (0.5 to 10µm),
nano (10 to 50µm), micro or net (50 to 500µm) and macroplankton
(>500µm).
Phytoplanktons are chlorophyll bearing suspended microscopic organisms
consisting of algae with representative from all major taxonomic phyla; the
majority of members belong to Chlorophyceae, Cyanophyceae and
Bacillariophyceae. Their unique ability to fix inorganic carbon to build up
organic matter through primary production makes their study a subject of prime importance. The quality and quantity of
phytoplankton, and their seasonalsuccession patterns have been successfully utilized to asses the quality of water and its
capacity to sustain heterotrophic communities.
Collection ofplankton
Collection of nano plankton
The nano plankton compared to net plankton has less number of species flagellates diatoms which have a size range of
5-20µm contribute more than 90% in the phytoplankton biomass.
Methods of collection
1. Bottle sampler
2. Pump and hose
Bottle sampler
Bottle samplers are ideal for small quantitative phytoplankton collection. It is mainly used for the collection of water
samples from any desired depth of shallow ecosystem from a stationary vessel – near shore waters,estuaries and
mangroves. Surface water can be obtained by gently scooping water in to a container of suitable size from the leeward
side of the ship. Subsurface water can be obtained by using sampler like Mayer’s Water Sampler, Friedenger’s Water
Sampler, Nansen reversing water sampler, Vaan Dorn water sampler, Niskin water bottle, NIO water bottle, Universal
water sampler, etc. Samplers are sent to a desired depth on the rope in an open condition. Messengers are sent to close
the lids to secure and lift the sample onboard.

73
Pump and hose
Pump and hose is used to collect water sample for quantitative plankton analysis from the
desired depth. An electrically operated rotary pump or centrifugal pump having flexible inlet
and outlet hose pipes is suitable. The water is taken on to the vessel from the desired depth
and transferred to sedimentation chamber or poured through one or severalhand nets of
various mesh sizes. The plankton collected from different bag nets is preserved for further
analysis.
Methods of concentration
1. Mesh filtration
2. Centrifugation.
3. Settling sedimentation
4. Membrane filtration
Mesh filtration
1. Fixed volume of water is passed through a mesh of about 200µm mesh size
2. Then the micro zooplankton in the water is
concentrated with small conical nets of fine gauge
(20-25µm mesh size)
3. Small flagellates, ciliates, diatoms, etc. pass
through the 20-35µm mesh
4. This fraction of the sample can be concentrated
by centrifugation, settling or settling filtration
methods
Centrifugation
1. 10-20ml of the water sample is centrifuged for about 15-30min at 1500-2000rpm with centrifuge.
2. The supernatant water is removed until the volume reduced to 1/10-1/30 of the initial.
3. The plankton is re suspended in the remaining volume of water.
4. The sample is fixed and preserved in neutralized formalin or Lugol’s solution for subsequent analysis.
Sedimentation
1. After the filtration, the organisms are allowed to settle and undisturbed for 1-2 days
2. Supernatant is carefully siphoned out
3. This process may be repeated until the sample is concentrated to 10-25ml
Membrane filtration
1. A known volume of water is filtered through a membrane filter of 0.5-1.0 µm porosity
2. The filtrate with filter is dehydrated by passing through the concentrated ethanol stained with alcohol (0.1% in 95%
ethanol) and finally washed with ethanol.
3. The filter is then cleared with creostone or immersion oil and mounted on a slide using Canada balsam or filtrate may
be subjected to immersion oil and taken for utermohl counting.
Collection ofnet (micro) plankton
Plankton of more than 50µm size can be collected by ordinary net sampling. This method could preferably used for
quantitative plankton collections, as large quantity of water is filtered. Net is towed vertically, horizontally, or obliquely.
Shape of nets commonly used is conical, conico- cylindrical and conical with a mouth reducing cone. Rectangular
shaped nets have been designed. The net is attached to the wire directly with a bridle. At the cod end of the plankton net,
a sampling bucket is attached.

74
Sampling methods
Vertical haul
In a vertical haul the entire water column is filtered through from the bottom to the surface,or only a top part is filtered.
The net is lowered to the determined depth from the anchored research vesseland" slowly hauled up. The hauling speed
is determined principally by the mesh width of the net (1 m/sec for a 300 µ size net), a weight is attached to the net
bucket.
A net is lowered to a fixed depth from a stationary boat and immediately pulled upward at a speed of 0.7-1.0m/sec.
When a net is lowered from a research vessel,the mouth rings of the net is folded vertically and descended smoothly
with the help of weight (10-15kg).
Horizontal haul
The horizontal haul is used to obtain plankton samples from a particular water layer. A weight holds the net while it is
being towed in the depth. The depth position of the net can be determined
from the wire angle and the length of the cable paid out. Net is hauled horizontally behind the vesselat a speed of
1m/sec.
Oblique haul
The net is lowered to a particular depth from a stationary vessel. Afterwards the vesselis slowly moved forward. The
net would come up to the surface filtering' an oblique column of water. The advantage of this method is that the water
column is more intensively filtered in this manner than in a vertical haul. In another type of oblique haul, the ship will
be in motion while the net is being lowered as well as hauled up. The net were towed obliquely from a desired depth
towards water surface during a boat is moving. It is done by slowly releasing plankton net from water surface to the
given depth and then tow at that depth for a while before pulling the net towards the water surface.
Preservation ofplankton
After the collection of plankton, the samples should be preserved immediately. For determination of chemical
composition, specimens should be fixed within 10 min after collection. For taxonomic studies samples should be
narcotized, fixed and preserved in this order. Otherwise autolysis, bacterial
action, cannibalism or chemical deterioration will set in.
a. Norcotisation (relaxation)
Norcotisation is a vital process before fixation and preservation. It is to
prevent from contraction and distortion of organisms at the time of fixation
and ensuring easy identification of the organisms.
Preparation of Norcotics :
1) Osmic acid : Dissolve 200mg osmium tetroxide in 10ml of distilled water
2) Formalin (20%) : Dilute 200ml of 40% formaldehyde solution to 800ml of
filtered water in a beaker. Add 0.5g borax (sodium borate +6.5g disodium
hydrogen sulphate). Allow the solution for 24 hrs for settlement. The
supernatant solution is siphoned out and used.
3) Menthol crystal
4) Magnesium chloride
5) Acetone-chloroform
6) MSS-222 etc
Procedure
1. Menthol - Small flakes of menthol are dropped on the surface of the sample. The crystal will gradually dissolve and

75
anaesthetize the plankton.
2. Formalin - Animals are placed into a volume of water 50-500 times their own volume. Add 3 drops of 2.5% formalin
to each 100ml of sample for 15min for the first hour. Add 6 drops in the second hour and 12 drops in the third hour at
15min intervals.
3. Propylene and phenoxytol - Add 3 drops of concentrated propylene phenoxytol into 1 litre of water containing
plankton.
I. Fixation
Fixation is the application of a chemical (fixative) to kill an organism but to retain its morphological characteristics as
far as possible.
Preparation
Buffered formalin : Add 30g of borax (sodium tetraborate ) to 1000ml of 40% formaldehyde and mix well. Allow the
solution to stand for 1-2 months. Filter the solution to remove the borax precipitate.
Steedman’s fixative : Dissolve propylene phenoxytol in propylene glycol in 0.5:4.5(v/v). To this solution add 5 volume
of Buffered formalin (undiluted)
Glutaraldehyde : Dissolve 8g of glutaraldehyde in 100ml distilled water and neutralize the solution with 1N Na OH
solution and preserved at 4oC. Supernatant solution is used as fixative.
Rodhe’s iodine solution: Add 10g of iodine, 20g of potassium iodide and 20ml of acetic acid to 200ml of distilled water
and mix well.
Procedure
1. Micro plankton
• Flagellates : add 1-5 % (v/v) of buffered formalin.
• Micro zooplankton: add 5-20ml of glutaraldehyde to 100ml of sample.
• Ciliates: add 5ml of Rodhe’s iodine solution to 100ml of sample.
• Phytoplankton: add 5 drops of osmic acid to 100ml phytoplankton sample.
2. Net plankton
• Sample is transferred in to a 500ml container.
• Add buffered formalin in the ratio of 5-90 parts (v/v)
• Invert the sample bottle after adding fixative for dispersing
• Add 5/ (v/v) formalin solution.
• In case of steedman’s fixative –the sample to fixative ratio should be 10:90 (V/V)
• The pH of both solution should be maintained around 7.6 to 8.3
II. Preservation
Preservation is the maintenance of fixed condition for extended periods of time. Specimens after one week fixation are
used for preservation after thorough washing with distilled water.
Preparation
1. Lugol’s solution
Dissolve 10 gm of potassium iodide, 5 gm of doubly sublimed iodine in 20 ml of distilled water. To this add 50 ml of
distilled water and 5gm of sodium acetate or 5 ml of 10% of acetic acid. Then the solution is made up to 100ml with
distilled water.
2. Ethanol solution
Prepare 30 %,50 % and 70 % with distilled water
3. Steedman’s preservative
Buffer formalin (undiluted) – 2.5 ml + Propylene phenoxytol – 1 ml + Propylene glycol- 10ml + Filtered water (88.5ml)
Procedure
1. Buffered formalin – 2.5 – 5 % formalin is used in ratio of 1:9 (sample to preservative). pH should be maintained at 7
2. Ethanol – One week after fixation wash thoroughly in distilled water before transferred into ethanol. The specimen is
then immersed in 30 % ethanol for 10 min; move to a 50 % solution and after 1 hr transfer to 70 % solution.
3. Lugol’s solution – Add 1- 2 ml of preservative to 1000ml of phytoplankton sample.
4. Osmic acid – Add 3-6 drops in 100 ml phytoplankton sample.
5. Glutaraldehyde – Preserve phytoplankton in the ratio of 1:1
Note : To preserve the natural colour of the plankton, fish and crustaceans may be preserved in phinolic antioxidant such
as 40 % emulsifiable concentrate of butylated hydroxyl toluene or butylated hydroxyl anisole (BHA).
Storage ofsample

76
Container such as glass bottles with wide mouth, polypropylene with plastic screw on lid, polycarbonate containers,
whirl pack – polypropylene bag are commonly used.
• Store the sample in a dust free dark and cool place
• Maintain the pH between 6.5 and7.5
• Periodic checking for colour and pH is required
• The preservative should be changed if necessary.
Labels :
Water resistant papers are used for external and internal labeling with following information in each container. External
label should have bottle no, station no, date of sampling, day/night, sky, time, depth of sampling, type of net, mesh
aperture,type of haul, flowmeter reading, collector name etc. and internal label should have station no, date of sampling,
sampling depth, type of net, mouth size and mess size, type of haul, number of turns in flowmeter, collector’s name, etc.
Identification ofphytoplankton
1. Chlorella
Cells spherical to ellipsoidal, solitary or aggregated,small smooth walled, chloplast single parietal, cup-shaped or
laminate, with or without a pyrenoid, reproduction by autospores, free living or symbiotic.
2. Pediastrum
Colonies stellate to disc-shaped, monostromatic disc entire or perforate,cells 4 to 128, polygonal, marginal cells mostly
with one, two or four processes,chloplast single parietal with a pyrenoid, diffuse in mature cells with one or more
pyrenoid, cells multinucleate, reproduction by zoospores and isogamets, planktonic.
3. Coelastrum
Colony hallow sphere, rarely polygonal to pyramidal, cells 4 to 128, radially arranged,spherical, ovoid or pyramidal,
closely adjoined and interconnected by narrow processes forming intercellular spaces,chloroplast cup-shaped to diffuse
with a pyrenoid, reproduction by autocolonies, planktonic.
4. Ankistrodesmus
Cells acicular or cresent shaped,solitary or in small loose groups, usually not enclosed in a mucilaginous envelope, cells
straight or curved, often twisted around one another, wall smooth with gradually tapering ends, spines lacking,
chloroplast single, parietal with or without pyrenoid, reproduction by autospores, planktonic.
5. Clostridium
Cells solitary or in loose aggregates,semicircular to lunate orcylindrical and involved with a short stout spine at either
pole, gelatinous sheath absent, cell wall relatively thick, chloroplast single, large and usually with a pyrenoid,
reproduction unknown, planktonic.
6. Selenastrum
Colonies without an outer mucilaginous envelope, consist of 4, 8 or 16 cells, cells arcuate to lunate with convex faces
apposed, apices acute,chloroplast single, parietal, lying along the convex wall, with a pyrenoid, reproduction by
autospores, planktonic.
7. Kirchneriella
Colonial, gelatinous, envelope homogeneous, cells lunate to sickle shaped with pointed ends or irregularly spirally
curved cylinders with rounded ends, cells usually in even numbers, chloroplast single, parietal usually with a pyrenoid,
reproduction by autospores, planktonic.
8. Scenedesmus
Colonies flat plate like, 2-4-8 (rarely 16-32) celled, cells in one plane, multiplies of two, cells acicular, ellipsoid, ovoid
or cylindrical (never globose), cells arranged in a single or double series of alternating cells with long axis parallel to
one another, cell wall smooth or granulate, with or without lateral ridges, teeth or spines, chloplast single, laminate with
a pyrenoid, cells uninucleate, autospores form autocolonies, planktonic.
9. Crucigenia
Colony enclosed by a thin inconspicuous gelatinous envelope, cells flattened, spherical to rhomboidal, quadrately
arranged with a large or small open space in the centre, frequently form multiple colonies of 16 or more cells, cell wall
without ornamentation and spines, chloplasts 1=4, parietal or disc-shaped and usually with a pyrenoid, reproduction by
autocolonies and akinetes, planktonic.
10. Tetrastrum
Colonies flat plate like, always 4 celled, cells triangular, cruciately arranged with or without an open space at the centre,
lie in a thin gelatinous matrix, angles rounded (never lunate), with one or more setae,chloplast 1 to 4, parietal with or
without pyrenoid, reproduction by 4 autospores which form autocolonies, planktonic.

77
11. Ulothrix
Simple unbranched filaments of indefinite length, basal cell present, cells uninucleate, mostly cylindrical, often broader
than long and never in pairs, terminal cell never pointed, chloplast single, riddle shaped parietal band, partially or fully
encircling the protoplast, pyrenoids one or several, reproduction by fragmentation, bi- or quadriflagellate zoospores or
biflagellate gamets, epiphytic or planktonic.
12. Microspora
Filaments unbranched, usually sessile when young or free floating, protoplast enclosed by the conjoined halves of two
successive H-pieces,each protoplast surrounded by thin cellulose layer, interpolation of H-pieces in diving cell, H-
pieces impregnated with silica, outer most layer of filament is made up of pectin, cells uninucleate with a central
vacuole, chloroplast in young cells irregularly expanded and perforate and reticulate sheet,without pyrenoid, zoospores
bi-or quadriflagellate.
13. Cladophora
Filaments repeatedly branched with basal-distal differentiation in the habit of branching, lateral branches arise close to
the upper septa and often appear to be bi or trichotomous (due to evection), cells 5-20 times longer than breadth,
multinucleate, cell wall thick and stratified, reticulate chloroplast with pyrenoids at intersections, reproduction by
quadriflagellate zoospores and biflagellate gamets, mostly attached rhizoidal branches when young.
14. Pithophora
Filaments branched, lateral branches arise a short distance from the upper septa,cells cylindrical, coenocytic, cell wall
thick but without lamellation, apical cell prominent, cylindrical akinetes common, intercalary or terminal, only half cell
takes part in their formation, free floating.
15. Mougeotia
Filamentous, cells conspicuously longer than breadth, chloroplast laminate, axial plate like, mostly one, pyrenoids
many, conjugation usually scalariform, zygospore always formed in conjugation tube, adjoined by two or four cells,
gametangia with cytoplasmic residues and without gerlatinous material after zygote formation.
16. Zygnema
Unbranched filaments of short or long cylindrical cells, chloroplast two, stellate, each with a central pyrenoid,
gametangia not filled with gelatinous material after zygote formation, zygospore either in the conjugation tube or in one
of the gametangium
17. Spirogyra
Filaments long, unbranched, cells as long as broad or severaltimes the breadth, chloroplast 1 to 16, parietal, ribbon
shaped with half to 3 or rarely 8 left hand spirals, pyrenoids many in a single series, lying equidistant from one another,
gamets physiologically anisogamous, aygopore in either of the conjugating cells.
18. Closterium
Cells solitary, elongate without a median constriction, poles distinctly attenuated but without spines, chlorplasts two,
sickle shaped, with or without longitudinal ridges, pyrenoids mostly few.
19. Cosmarium
Cells compressed,oval to spherical with a deep median constriction, length slightly greater than the breadth, cell wall
smooth or ornamented, semicells without spines, apex not incised, each semicell with single axial chloroplast with four
radiating plates, pyrenoids axial in position.
20. Staurastrum
Cells strongly compressed,bilaterally or radially symmetrical, deeply constricted with acute-angled sinus, cell wall
smooth or ornamented, apex of semicells extended into 2 or more divergent arms, chloplast axial pyrenoids one to
many.
21. Desmidium
Filamentous unbranched, spirally twisted in gelatinous envelope, cells broader than long, triangular or quadrangular in
vertical view, without deep median constriction, cell wall smooth, chloroplast axial, with a lobe (deeply incised) and a
pyrenoid in each angle of a semicell.
22. Tetmemurous
Cells solitary, cylindrical to fusiform, median construction with open sinus, length 2 to 8 times the breadth, apex of
semicells rounded with a vertical incision, cell wall smooth, punctuate or minutely scrobiculate, without transverse rings
of spines or verrucae,chloroplast single, axial with many longitudinal radiating plates, pyrenoids many, axial and
arranged in a row.
23. Xanthidum

78
Cells solitary, compressed, median constriction deep, semicells with 1 to many simple lateral spines, middle front of
semicells wall thickened, semicells not incised at apex and with two laminate axial or four parietal chloroplast,
pyrenoids usually one.
24. Arthrodesmus
Cells solitary, length and breadth about equal, strongly compressed, deeply constricted, sinus widely open to linear, cell
wall uniformly thick and smooth, with straight or strongly curved spines at angles, chloplast axial laminate, pyrenoids 1
to 2.
25. Penium
Cells solitary, cylindrical with parallel sides and rounded or truncated poles, long axis straight, mostly without a median
constriction, more than one gridle piece in each semicell, striae or puncate in regular longitudinal rows, semicell with
axial chloroplast, pyrenoids on to many.
26. Gymnozyga
Unbranched filamentous, often with a gelatinous sheath, cells barrel shaped, length double the width, median
constriction very slight, semicells inflated at the base and flattened at the apices, base and apices with or without
longitudinal striae, chloroplast axial, pyrenoid single.
Euglenophyta (Euglenoids)
27. Euglena
Cells uniflagellate, fusiform to acicular, flexible, constantly change their shape, posterior end more or less pointed,
gullet and eye spot anterior, contractile vacuole 1 to many. Chloroplasts many, discoid to band shaped, pyrenoids may
be present,flagellum bifurcated at base,neuromotor apparatus present, planktonic.
Pyrophyta
28. Peridinium
Cells slightly flattened dorsoventrally, hypotheca with 5 postcingular and 2 antapical plates, epitheca with 6 to 7
precingular, none to 8 inercalary and 3 to 5 apical plates, plates usually ornamented with spines or reticulum of small
ridges, sutures broad with striations which are often longitudinal or transverse,planktonic.
29. Ceratium
Cells broadly fusiform, hypotheca with 5 postcingular and 2 antapical plates which terminate in posterior horns,
epitheca with a series of 4 precingular and 4 apical plates, apical plates form an apical horn, girdle transverse,ventral
plate large, membranaceous and anticulated with pre-and postangular plates, planktonic.
Bacillariophyta (Diatoms)
30. Melosira
Cells united to form long unbranched filaments, gridle sculptured, valves circular in vertical view, ornamentation in two
parts, concentric, cylindrical in gridle view, polar margins with denticulations, chromatophores many, discoidal,
planktonic.
31. Cyclotella
Cells usually solitary, gridle unsculptured, valves circular, ornamented in two concentric regions, outer peripheral
radially costate, inner smooth and irregularly finely punctuate, intercalary bands absent. Chromatophores many and
discoidal, planktonic.
32. Stephanodiscus
Cells solitary, gridle unsculptured, valves circular with radiately alternating punctuate and smooth areas,peripheral
portion with short spines which extend beyond the edge of the valve and multiseriate punctuate, rectangular in gridle
view, planktonic.
33. Coscinodiscus
Cells solitary, gridle unsculptured, valves circular to elliptical in valve view, irregularly ornamented with minute forking
rows of punctuate to coarse areolae,valve surface without radiate hyaline areas,denticulation at margin may be present,
rectangular in gridle view, planktonic.
34. Tabellaria
Cells generally in free floating zigzag chains, sometimes semistellate, septa more than two, longitudinal, straight,
perforate,present between gridle and intercalary bands, valves enongate, inflated laterally in the middle and at the poles,
transverse finely punctuate striae lateral to median pseudoraphe, planktonic.
35. Diatoma
Frustules lanceolate to linear in valve view, often subcapitate poles, valves bilaterally symmetrical in both axis, septa
transverse,many run across the valves to the inercalary bands of the gridle, pseudoraphe faint, valve and gridle

79
ornamented, planktonic.
36. Fragilaria
Cells attached side by side to form ribbon shaped colonies (rarely flat stellate), linear to fusiform in valve view and
rectangular in gridle view, bilaterally symmetrical in both axis, pseudoraphe present, valves with transverse striae or
punctae, planktonic.
37. Synedra
Frustules usually narrow,many times longer than broad, solitary or in radiate fan shaped free-floating or epiphytic
colonies, needle shaped in both views or with slightly capitates poles, valves linear to lanceolate, straight to curved,
pseudoraphe and transverse ornamentation present, apices truncate in gridle view, bilaterally symmetrical in both views,
epiphytic or planktonic.
38. Asterionella
Colonies stellate, cells in one plane, ends of valves flat, dissimilar in size, broader ends joined by gelatinous cushions,
indistinct pseudoraphe and transverse ornamentation present,planktonic.
39. Navicula
Frustules symmetrical, rectangular in gridle view, raphe and axial filed straight, latter is narrow and without any
expansion, lateral to axial field striae or punctuate in transverse rows,stauros absent, planktonic.
40. Pannularia
Frustules symmetrical, axial field broad and expanded next to the centraland polar nodules, raphe with somewhat
sigmoid or straight outer fissure, valves with smooth transverse costae,rectangular in gridle view, gridle smooth and
without intercalary bands, planktonic.
41. Gyrosigma
Valves convex, sigmoid, gradually attenuated,poles acute or rounded axial field raphe sigmoid, punctae in transverse
and longitudinal rows making a pattern of intersections, planktonic.
42. Pleurosigma
Similar to Gyrosigma, valves with one transverse and two oblique rows of punctae to the axial field.
43. Gomphonema
Frustules transversely asymmetrical in both views, raphe straight with centraland polar nodules, valves with transverse
rows of delicate or coarse punctae,frustules borne on tips of dichotomously branched gelatinous stalks, epiphytic or
planktonic.
44. Nitzschia
Frustules with tranverse septa,keel single, excentric, on lateral margin of valve, raphe lies within it, keeled margin of
one valve faces the unkeeled margin of the other valve, rapheal fissure with uniseriate row of circular pores (carinal
dots), planktonic.
45. Surirella
Face of valve flat or spirally twisted, valves with keel (containing raphe) on both margins and a pseudoraphe in the
middle, costae prominent, transverse,planktonic.
46. Microcystis
Colonies many celled, microscopic or macroscopic, spherical to irregular or net like, cells spherical, densely aggregated,
without evident sheaths and even distribution, pseudovacuoles often present, mostly planktonic.
47. Spirulina
Trichomes unicellular, without sheath and lack dissepiments, cells terminals round, usually not tapering, trichome,
regularly spirally coiled, spirals broad or narrow, planktonic.
48. Anabaena
Trichomes solitary or aggregated in a soft amorphous mucilaginous mass,never contorted like Nostoc, thickness of
trichome usually the same throughout, trichome with watery and inconspicuous sheath, heterocysts intercalary akinetes
single or in series.
49. Anabaenopsis
Filaments unbranched, short, spirally coiled, hetercysts terminal, at both the ends of the trichome and usually at different
stages of development heterocyst in pairs when intercalary, akinetes remote from the heterocysts,planktonic.
50. Nostoc
Trichomes within a definite sheath, contorted, colonical matrix firm with a definite shape,heterocyst, intercalary,
akinete solitary or in chains.
51. Oscillotoria

80
Trichome unbranched and without a distinct sheath, solitary and scattered or form expanded masses,trichomes may
dissociate easily, mostly straight or in irregular spirals, ends distinctly marked, attenuated, rounded bent or coiled and
with or without calyptras, cells discoidal or cylindrical, homogonia may have a thin sheath.
52. Lyngbya
Trichomes many celled, cylindrical, occur singly or interwoven, with thin but firm colourless or brownish sheath.
53. Phormidium
Single trichome within a thin watery or less sheath, cells barrel shaped, sheath of filaments agglutinated with one
another and trichomes do not dissociate easily, never grow in erect tubes, mostly subaerial, morphology and apical cells
much similar to Oscillotoria.
Protozoa (Rhizopoda)
54. Amoeba
Body shape irregular, asymmetrical and changes constantly, pseudopodi and body with ecto and endoplasm, lobopodia
many, indeterminate a directing locomotion, without shell or pellicle, covered with plasmalemma usually uni or
binucleate, single contractile and food vacuoles conspicuous.
Verticellidae
55. Vorticella
Body inverted bell shaped, solitary (never colonial), usually in groups stalk unbranched, long and contractile, it is
secreted by aboral tip, oral groove, circular around the edge of the cup and extends inward, plugged by a raised disc, two
circles of cilia on the disc, endoplasm with a long and horse-shoe shaped macronucleus and a small micronucleus,
colourless, green or blue
Collection and identification freshwater Zooplankton
Zooplankton, the microscopic free swimming animal components of aquatic systems,are represented by a wide array of
taxonomic groups; of which the members belonging to protozoa, rotifer, cladocera and copepod are most common and
often dominate the entire consumer communities. They are endowed with many remarkable features and are often
armoured with spines, which hamper their predation by higher organisms. The ability of movement not only provide
them an effective defense measure but also enable them to actively search and feed upon the phytoplankton. Their high
and rapid rate of parthenogenetic reproduction usually overcomes the predation losses and enables them to exploit algal
blooms. They constitute important link between primary producers and consumers of higher order in aquatic food webs.
Therefore,the population dynamics of zooplankton with reference to system provides key information for the
management practices.
Preparation of sample
• Collect known amount of water sample eg. 25 litre and filter through a plankton net of bolting silk of No. 25
• Transfer the net plankton in 50ml bottle and preserve in 5% formalin. Add few drops of glycerin to it.
• If further concentration is required allow the sample to stand for a day.
• Practically all the zooplankton will settle down at the bottom of the bottle.
• Remove supernatant plankton-free water with the help of pipette and reduce the sample to the designed volume.
Qualitative and quantitative analysis
Identify the zooplankton in the sample using keys and monographs.
1. Brachionus
Lorica dorso-ventrally flattened, anterior end with 2, 4 or 6 spines, posterior end angled, rounded or with 1 to 2 spines,
foot opening posterior, foot long, worm like, wrinkled annulated, flexible, sharply marked off from body, 2 toes forked
completely retracible within lorica, eye present, cosmopolitan, planktonic.
2. Keratella
Lorica thick, dorsally curved and ventrally flattened or concave,dorsal plate strong with polygonal facets,ventral plate
delicate, anterior spines – 6, symmetric, posterior spines mostly present, foot and toes absent,cosmopolitan, planktonic.
Cladocera (Water fleas)
3. Daphnia
Body compressed, valve surface squarish or rhomboidal, dorsal and ventral margins rounding over towards each other,
posterior part provided with a sharp caudalspine, head not separated from body by a dorsal notch, females with well
marked and pointed rostrum, small antennules, 3-4 abdominal processes-anterior one bent forward, tongue shaped and
long, males with large antennules and first leg with hook and long flagellum, lack rostrum.
4. Moina

81
Valves thin, somewhat rhomboidal, not covering wholly the thick, heavy body and post abdomen, posterior margin of
carapace without spine, cervical sinus present,head large, thick, rounded in front and bent downwards, without a beak,
fornix small, rostrum and ocellus lacking, in female abdominal projection horse-shoe shaped, post abdomen wide, bears
ciliated spines and bident, abdominal setae long, claw small, in male antennules long and stout, denticulate, oval
ephippium with 1 or 2 eggs.
Ostracoda
5. Cypris
Shells tumid, broad, length lesser than twice the width, shells covered with tubercles and hairs, left valve slightly larger
than the right, valve margins without irregular canalsystem, natatory setae of second antenna long and at least reach the
tips of the terminal claws, masticatory process with smooth spine like setae,second thoracic leg with
bent denticulate claw and its second segment with single seta,furca well developed, long, elongate
with subterminal and normal dorsal seta,whitish in colour.
Copepoda
6. Cyclops
Anterior part fatter and antennae comparatively shorter, first antennae 17 segmented, three distal
segments with row of fine hyaline spines, second antennae 4-segmented, first 4 pair of legs 3-
segmented, fifth pair of legs 2-segmented, the dorsal segment small, narrow and bears a long terminal
bristle and short or moderately long inner lateral spine, receptaculum seminis round, eggs sacs two, caudal ramus
usually with longitudinal dorsal ridge and inner margin armed with fine hairs.
7. Nauplius
Body oval unsegmented, smaller in size, do not resemble the parents, eye frontal, median, appendages incompletely
developed, typically three pairs, first pair (antennules) uniramose, second and third (antennae,mandibles) biramose,
furcal setae long, project on either side of the rear end, free swimming.
8. Diaptomus
Body slender, rami 3 segmented in first four pairs of thoracic legs except the first endopod which is 2-segmented,
endopod of 1st leg 2-segmented, 3rd and 4th legs 3-segmented, 5th leg biramos, rami 1 to 2-segmeted with or without
two apical setae and in male asymmetrical, endopod rudimentary, right leg ending in a single claw, furcal processes
short, divided into many sub-genera, freshwater,planktonic.
Enumeration and biomass estimation of freshwater plankton
Qualitative estimation of plankton :
Qualitative analysis of plankton involves three steps, they are Splitting,
Sorting, Counting
a. Splitting:
• Transfer well mixed sample in to the Folsom’s plankton splitter.
• Circular drum is moved back and forth to homogenize and to divide the sample into equal parts
• The well mixed representative subsamples are poured in to container or boats.
• The aliquot of each boat / container is the representative of the total catch
• The aliquot obtained from each container may further split depending on the concentration of the plankton.
b. Sorting:
• Well mixed representative sample is poured into a clean petridish.
• Place the petridish on the dark background
• Use hand lenses or eye pieces (10 x) to identify the bigger organisms.
• Individual specimens belonging to same genera or species are grouped together and preserved separately.
• Identify the specimens to generic or species level.
c. Counting:
• Remove all macro zooplankton in the sample.
• Measure the total volume of water and mix well
• Transfer 1 ml of water sample into Sedgwick rafter counting cell by using stempel pipette or wide mouthed pipette.
• Place the cover slip diagonally across the counting cell and introduce the sample from the corner. The cover slip
moves into its proper position by capillary action.

82
• The prepared cell is placed under microscope and allowed for sedimentation.
• The cell is moved horizontally or vertically along the first row of squares and the organisms in each square are
counted.
• Organisms are identified to genera/species and counted accordingly.
• If one lack sufficient time to count all the squares in the counting cell, count just a few transects considering the
homogenous settlement of the plankton.
• The total number of organisms are then computed by multiplying the number of individuals counted in these transects
with the ratio of the whole chamber area to the area of intercepted transects.
• For error free results take replicate counts.
Calculation:
The total number of zooplankton present in a litre is given by
N= n × v / V
Where : N = total number of zooplankton per litre
n = average number of zooplankton in 1 ml
v = volume of plankton concentrate (ml)
V = volume of total water filtered
Quantitative estimation of plankton
i. Volumetric analysis :
a. Settlement volume method:
• The plankton is allowed to settle by gravity and the space occupied by the settled material is taken as settled
volume.
• Concentrate the sample using a net. A known volume of sample is transferred into a graduated cylinder or
sedimentation / centrifuge tube.
• Mix well and allow the sample to settle for 1-2 days.
• The settled volume of the sample is recorded (cc).
• The volume of the sample s then calculated in m3
b. Displacement method:
• The space occupied by the plankton is measured in terms of the equivalent volume of liquid displaces.
• The sample is filtered through plankton net of known mesh size.
• The concentrated plankton is carefully removed and transferred to 25ml measuring jar.
• Pour the water from 25ml burette into the measuring jar till the 25ml marks is reached.
• Record the volume remained in the burette (cc).
• Displaced volume is equivalent to the plankton present in the sample.
ii. Gravimetric method:
It is the total weight of planktonic organisms concentrated from the known volume of water.
a. Wet weight
It is the raw weight of the planktonic organism with their natural body fluids.
• Plankton sample is screened through filters.
• Adhering water is blotter off with filter paper.
• Transfer the plankton matter to a pre-weighed aluminium foil.
• Weigh the sample near to a milligram.
b. Dry weight
It is the raw weight of the planktonic organism without water content.
• The plankton concentrate for which the wet weight is already known is placed in pre-weighed platinum dish
or silicon crucible.
• Dry in a electric oven at 60oC until all the water is evaporated
• The weight of the dish and contents are then weighed.
• The difference between the final weight and dish weight gives the dry weight.

83
Note : The best expression of plankton biomass is dry weight preferably ash free dry weight or carbon weight.
It is important to indicate the method of measurement along with results.
Estimation of Primary Productivity in freshwater bodies
The primary production in the aquatic ecosystem starts with the synthesis of organic compounds from the
inorganic constituents of water by the activity of plants / phytoplankton in the presence of sunlight. The
inorganic constituents which form the raw material for this synthesis are water, carbon dioxide, nitrate ions,
phosphate ions and various other chemical substances. The products are mainly carbohydrates and proteins
and fats in very small quantities. Organic production by plants is the first step in tapping energy by living
beings from non-living natural resources and hence called primary productivity.
The method of estimating primary productivity by dark and light bottle method was introduced by Garder and
Gran (1930). In this method, the water samples are incubated for a certain period in light and dark bottles
which are then suspended at the same depths from where the sample are taken. In light bottles, oxygen is
released as a result of photosynthesis and a part of oxygen is used for community respiration. In the dark
bottles, only oxygen consumption takes place as a result of respiration. The amount of oxygen liberated by
phytoplankton during photosynthesis is considered as a measure of primary production.
Material required
BOD bottle (2 light / transparent and 1 dark), Nylon or Jute ropes, Burettes, Reagents (Manganous sulphate
solution, Alkaline iodide azide solution, Sodium thiosulphate, Concentrated Sulphuric acid, Starch indicator
solution) etc.
Procedure:
a. Fill three BOD bottles with water sample in round stoppered bottles (1 Light bottle, 1 dark bottle and 1
control light bottle) avoiding air bubbles.
b. Water sample in the control bottle is immediately fixed by using Winker’s fixatives
c. The dark bottle is wrapped with aluminum foil and kept in a black bag to protect from light.
d. Use one of the light bottles for estimating the initial dissolved oxygen As control)
e. Suspend both light and dark bottles exactly at the depth from where the sample was drawn are then
suspended on to a raft and anchored.
f. The bottles are normally incubated for a period of 3-4 hrs between dawn to midday or sunset in the
respective depths
g. At the end of incubation period, the bottles are retrieved and fixed with oxygen fixatives.
h. The oxygen content in the sample is determined by using Winkler’s method.
Calculation
Let the initial oxygen level be- IB
Let the final oxygen level in dark bottle be - DB
Let the final oxygen level in light bottle be - LB
Net oxygen production - LB – IB
Oxygen consumed for respiration - IB – DB
Gross production of oxygen - LB – DB
Let ‘t’ be the number of hours of incubation
Therefore the Primary productivity can be calculated from the formula
LB – DB x 1000 x 0.375
Gross primary productivity = ____________________________ mg C/m3/hour
1.25 x t
LB = IB x 1000 x 0375
Net primary productivity = _____________________________ mg C/m3/hour
1.25 x t
IB – DB x 1000 x 1 x 0.375
Community respiration rate = __________________________ mg C/m3/hour
t

84
Collection and identification ofbenthos from inland water bodies
The heterogenous assemblage or organisms attached or resting on the bottom or living in the bottom sediments of a
body of water are known as benthos. Phytobenthos and zoobenthos are the terms used for benthic plants and animals
respectively. The term benthos is widely referred to flora and fauna which are intimately associated with sediments in an
aquatic system. Benthic environment represents bacteria,plants and animals including bottom living fishes from all
phyla and their sizes widely varied. Benthic organisms are,in general sessile and slow moving in nature. About 75% of
benthic animals live on firm substrates (rocks, corals), 20% occur in sandy / muddy bottoms and only 15% of the total
are planktonic.
Most of the benthic organisms are detritivores and form an important life in the food chain on account of their ability to
convert low quality and low energy detritus into better quality food for higher organisms in the food web. By virtue of
being relatively stationary, they are constantly exposed to changes in the mud-water interface and respond very well to
it. Therefore, severalpollution indices have been proposed using qualitative and quantitative change in benthic
populations.
In the collection of benthos the samplers should be such that they penetrate well into the sediments to a sufficient depth
in order to capture the organisms inhabiting in that area. The benthic samplers are of mainly two types, viz., grabs and
core samplers.
Peterson grab : It is consisting of two hinged pincer like buckets which are sent down to the sediments in open
condition. As the drawing line slackness, the release mechanism is activated. In retrieval, the two buckets come together
and thus a semi-circular section of sediment is cut and entrapped. The drawing line is then pulled and the grab which is
now in a closed condition is made open in a tray or bucket.
Ekman- Birge grab : This is the commonest grab devised for use in muddy bottoms by Ekman (1911) and Birge
(1922). The two shovels which are kept open against very strong spring action by means of two chains are closed from
the above by means of a weight (metallic messenger). Immediately after this operation, one can pull the grab out of the
bottom and finally out of the water column. It is very heavy and made of brass in order to avoid rusting in the water. The
upper portion is box shaped and it is closed by two movable covers which fall in under the pressure of the water when
the grab is sent down. The basalsurface of this grab is about 250cm2
.
Van Veen’s grab : It is also a very convenient and reliable grab devised by Van Veen (1936). The working principle of
this grab is more or less similar to Ekman-Birge. However,it is held open by a small bar and is not operated by a
metallic messenger. During operation, the grab is sent down the bottom when the two shovels out so that the bar is
released automatically. The draw rope is attached in such a way that with the pull from above, the two shovels of the
grab are made to close tightly with mud sample entrapped in it. The basal area of this grab may be 1/20m2
.
Core sampler : It consists of metallic tube of 50 cm length and 3cm diameter and is loaded at the top with a heavy lead
weight. A valve present at its upper end allows the water in the tube to escape upwards when the corer is sent down to
the bottom and it closes again when the tube is pulled up. The lead weight drives the tube strongly in to the mud, so that
a profile of the bottom sediment is cut out. The sample is later removed from the tube with a rod.
Identification ofbenthos
Oligochaeta
1. Chaetogaster
Body very transparent, anterior part broader, postomium well developed, in some bluntly pointed with stiff sensory
hairs, dorsal setae totally absent,2 bundles of hooked setae on the ventral side of each segment, no bristles in the
segments 3 to 5, blood colourless, commonly associated with tubes of insect larvae.
2. Nais
Head distinct, both dorsal and ventral setae present,dorsal setae long, hair like, start at segment 6, not serrate,similar in
length, ventral setae short and with cleft ends, of segments 2 to 5 mostly well differentiated than the posterior segments,
posterior end not forming retractile appendages, blood yellow or red, only anterior body segments with lateral
commissural blood vessels, spermatothecae in the same segments where testes are situated, body somewhat transparent.
3. Dero
Setae similar to Nais, posterior end modifies into a ciliated gill bearing retractile respiratory organ, the branchial area
without long process or palps, blood reddish, eyes absent often in tubes.
4. Aulophorus
Dorsal and ventral setae as in Nais, posterior end modified into the respiratory organ, the branchial area,ventral margin
of branchial area with long processes or palps.

85
5. Stylaria
Prostomium long, tentacles like, forming a long conspicuous narrow proboscis, a pair of eye spots present,setae an in
Nais, dorsal setae begin in 5th or 6th segment.
6. Lumbriculus
Worms usually red or brown in colour, prostomium not elongated into a proboscis, paired setae on both surfaces of the
segments, all of one form, forked at the end, distal tooth smaller than the proximal, dorsal blood vessels with paired
contractile blind appendages, two pairs of sperm ducts with a pair of openings.
7. Branchura
Body may be reddish, fairly stout, very contractile, prostomium bluntly conical, ventral setae cleft,dorsal bundles
comprised of 1-3 hairs, 5-8 needles forked in anterior region, anterior segments smaller, increasing posteriorly, with
small at the tip, posterior segments with a dorsal and a ventral gill, gills non-ciliated, last segment without gill, live in
tubes.
8. Tubifex
Worms reddish, coils into balls by slight disturbance, anterior end embedded in mud, waves the posterior end in water
for aeration, segments clearly demarketed, prostomium short, triangular, tips pointed, eye spot and cilia absent, dorsal
bundles with forked and usually hair setae,setae on ventral bundles usually forked, two lateral teeth of dorsal pectinate
setae widely divergent, live in tubes.
9. Tipula
Larvae large, about 3 cm or more when extended, head retractile, head capsule broad and massive, non-sclerotized
posteriorly and often also ventrally, last abdominal segment has rectangular plate surrounded by 6 to 8 lobes, anal gills
not pinnately branched, pupa with long breathing horns.
10. Antocha
Head capsule slender, spiracular disc with 2 ventral elongated lobes and the rest reduced or vestigial, spiracles lacking
or vestigial, larva and pupa enclosed in silken case,pupal respiratory tube 6 to 8 branched.
11. Psychoda
Body more or less cylindrical, without sucker discs, intermediate body segments without spiracles, thoracic and
abdominal segments secondarily divided, at least terminal abdominal segments with sclerotized plates, preanal or
prosternal plates absent, adanal region with a transverse plate, dorsal plates usually less than 26.
Mollusca
12. Lymnaea
Shell thin with a prominent acute spirae, dextral, large often flaring aperture,columella hoisted, tentacles flattened on
pair with eyes at their base,lip simple, acute,inner lip of aperture smooth, radula composed of 3 pieces, one large
transversely elongated and two small, foot rounded behind.
13. Gyraulus
Shell discoid, small, apparently dextral, orbicular above, flat beneath, whorls few,rounded to carinate, rapidly
increasing, shell with rounded periphery, shell compressed vertically so that aperture is much greater in breadth than
height (oblique), somewhat deflected, tentacles cylindrical, jaws in 3-segments, radula with numerous teeth.
14. Pisidium
Shell small, oval to round thin, greenish or yellowish,3 cardinals, one cardinal in the right and 2 in the left wall, siphon
two, short consolidated into a single tube, umbo back of the middle, directed backwardly, foot flattened, tongue shaped,
capable of great extension.
15. Corbicula
Shell triangular, thick, equilateral, having the beaks central, outer surface with rather concentric ridges, lateral teeth
serrated,2 cardianal teeth in each valve.
16. Lamellidens
Shell nacreous,equivalve, oval, anterior end rounded posterior more or less pointed, umbo towards the anterior end,
hinge teeth consisting of cardinals and posterior lateral, siphones short, complete, adductor muscles two, equal in size,
foot large, byssus in young, cosmopolitan, freshwater in habit.

86
Enumeration and biomass estimation of benthos from different freshwater bodies
Collection and preparation of sample: Since benthos dwell at or below the surface of the bottom sediments of
littoral and profundal zones, they are collected with the help of mud samplers.
Requirements : Mud sampler, Oven, Muffle furnace, Crucibles, Sieve (2mm and 0.5mm mesh size), Bucket,
Hand-lens, collection bottles, forceps, 70% alcohol (preservative), Whatman ash free filter paper, etc.
Method
 Collect sediment sample by suitable mud sampler
 Take the sample in a bucket, note its volume and add water to it.
 Sieve out the suspension through 2mm and 0.5mm mesh size sieves, one after the other.
 Collect the micro and macro invertebrates from the sieve with the help of forceps and transfer them to
a wide mouth bottle containing 70% alcohol.
 Transport residual organic matter retained in the sieve to the laboratory and 50 to 100ml of water to it.
 Dissolve 5gm of sucrose in it. (This helps in easy collection of benthic fauna. Because they now float
on the surface due to change in the density of the medium).
 Alternatively, the colouring of dyes of the organism (by treating residual matter with 0.1- 0.2% eosin,
erythrosin or acid fuchsin in 70% alcohol) helps in easy collection of smaller organism like
Oligocheats, Chironomids, Nematodes, etc. which pose a greater problem in comparison to Sponges,
Mollusks, Arthropods and others.
 Fix the organism in 70% alcohol
 Qualitative and Quantitative analysis
 Identify the organism using keys and monographs.
 Count their numbers species-wise in the sample and note.
 Keep the organism species-wise on pre-weighted ash free filter paper and transfer to a crucible of
known weight.
 Deduce the fresh weight of the material and transfer to a dust free oven at 105 2oC till you get a
constant weight.
 Cool in desiccators, weigh and deduce the dry weight.
 Keep the crucible with the contents in a muffle furnace at 550oC for 6-8 hours.
 Cool in a desiccator, find out ash content and note.
 Calculate the number of organisms per unit area and the biomass species-wise and for total benthos.
Observations :
1. Site of collection :
2. Locality :
3. Depth (m) :
4. Date of collection :
5. Type of sampler :
6. Area of sampler (cm2) :

87
Calculations:
Individual m-2 = (N/a) x 104
Where N = Average number of organism per sample
a = area of sampler (cm2)
Result: Express number of total benthic organism per m2 and total benthic biomass as OM g/m2.
Biomass of benthic animals
For collecting benthic animals belonging to deeper muddy areas (15-20 cm deep), corers of 71cm2 are ideal.
After operating the corers in the specific areas, the corers should be washed through a screen with openings of
6 mm square and the organisms are separated by hand from the material that the screen retained. This screen
could retain all the organisms weighing 0.2 gm. The smaller farms would also be entangled in the debris on
the screen. The organisms are separated into taxonomic groups, counted and weighed intact after blotting with
paper. These live weights, which may include inorganic shells and the water trapped within the body cavities,
should be multiplied by appropriate factors to convert them to weights of dry tissue. The factors are obtained
by drying representative species at 105oC for about 24 hrs. prior to drying, molluscs, crustaceans etc. should
also be decalcified by immersing them in 20% HCL until all hard parts are dissolved.
Collection and identification ofaquatic plants from different freshwater bodies
The plants vary greatly in the degree to which they have become truly aquatic and present in an interesting series of
gradations from those which are little more than amphibious, living at the edge of the water in very moist or water
saturated soil. Aquatic plants are those unwanted and undesirable vegetation which reproduce and grow in water and if
left unchecked may choke the entire body of water posing a serious menace to pisciculture. Another definition is that the
surplus growth of a plant that influences adverse physical, chemical and biological effects on a water body with its
resultant economic and aesthetic losses.
Collection ofAquatic plants
The aquatic plants can be collected using a long handled hook, nets or by hand. For quantification of sample in a given
area the floating or sinking type of quadrates of known size namely (1m x 1m or 0.5m x 0.5m) made up of PVC pipes or
wood are used. These quadrates are placed to mark the area from which sample is to be taken. After collection, these
plants are brought to the laboratory for identification. Before identification of these plants, they must be classified based
on their habitat into the following classifications, they are :
i. Floating macrophytes
ii. Marginal macrophytes
iii. Submerged macrophytes
iv. Emergent macrophytes
Identified ofplants using the following keys :
i. Floating macrophytes
1. Eichhornia sp (Water hayacinth or blue devil)
Class : Angiosperm
Family : Pontederiacea
It is native of Brazil, accidentally brought to India and released in West Bengal, one of the most damaging aquatic
weeds,inhabits stagnant and slow moving rivers.
Leaves broad with swollen stalks filled with air to enable them to float on water surface,dense leathery roots, flower
pinkish in colour, multiplication by vegetative propagation, dries off in winter and spourts during summer.

88
2. Salvinia (water fern velvet)
Family : Salviniaceae
This plant has got rhizome, stalk or stem is delicate, oblong or hemispherical leaves, actual roots absent, leaves sessile
with short stalk, leaves in two or more whorls, second whorl is either lateral and floating, third one submerged in water
which looks like roots, lateral leaves sometimes filled with air which aids in floating.
3. Pistia (water lettuce)
Family : Araceae
A free floating perennial plant, plant body comprise a shell like rosette of tongue shaped leaves, reduced stem, sessile
leaves and numerous branching roots, leaves form common cup shaped structure,leaves ovate and surrounded at the
base by membranous sheath.
4. Lemna (duck weed)
Light green in colour, occurs in group of one to three, no distinct stem, leaves have flattened, minute leaf-like fronds,
vegetative reproduction is rapid, often forming a scum over the surface,flowers are rare and so small that they are
invisible to naked eye, appear as small weeds.
5. Azolla (water velvet)
Family : Azollaceae
Smaller plant, found in stagnant water bodies, leaves lobed, scale like, thick and about 0.5 mm in length, the entire plant
is 1.5 – 2.0 cms in length, impart reddish green colour to water surface by covering it, it fixes atmospheric nitrogen.
ii. Marginal macrophytes
1. Colocasia
Family : Araceae
This plant covers large areas of the water body, leaves ovate, 6-20 inches long and 3-12 inches wide, leaf margin dark
green in colour, base of stem triangular, petiole long up to 3-4 inches, colour of petiole green, violet or purple.
2. Typha (Cat tail or Elephant grass)
Family : Typhaceae
Common in margins of ponds, lakes, rivers and canals, perennial, creeping rhizome with leaves growing up to 2 m
height and leaves have sheath at the base. Leaves bi-serrate,thick and spongy, secreting organ present at the leaf base,
flower numerous and cylindrical.
3. Marsilea (water shamrock)
Family : Marsiliaceae
It inhabits ponds, rooted in shallow and stagnant waters,roots slender, stalks slender and thin, roots burrowed into the
ground, petiole long with four cloves like or sharp pointed leaflets.
4. Scirpus (Bullrush)
Family : Cyperaceae
Annual herb, triangular in cross section, stem bears sheath at the base but sometimes leafy and naked, spiklets numerous
with one or more long leaves from the base of branch, spiklets are usually with more flowers.
5. Cyperus (Flat sedges)
Family : Cyperaceae
Perennial herb with a single stem, cylindrical in cross section and hallow. The stem has sheath at the base and with one
or more leaves on top forming a cluster, flowers or spikltes are present at the top.
iii. Submerged macrophytes (Rooted)
1. Hydrilla
Family : Hydrocharitacea
It is found to occur in almost all water bodies in India like ponds, lakes tanks etc. Leaves linearly arranged in whorls
while stem is slender, grows up to 45 cms, has got fibrous roots, multiplies very rapidly by spores and vegetative
propagation, infestation density is 20-30 kg per square meter, broken parts of this plant develops into a new plant by
attaching themselves with the help of roots, provides shelter to young fish in aquaria offer a substrate for attachment of
spawn of common carp.
2. Chara (stonewort)
Occurs in all types of freshwater bodies, stem has got erect branches and are gregarious in habit, nodes and internodes
can be easily distinguished, grow up to 15 – 30 cm in length, remains unattached to the bottom, plant is rough to touch.
3. Vallisneria (eelgrass / tape grass)
Plant with long ribbon like leaves measuring 0.5 – 1 m width, female flowers are long, thread like, twisted and appear at

89
stalks, propagation is by offshoots, it can tolerate temperature of 25 – 30o
C and medium water hardness.
4. Ceratophyllum (Horn wort) - (Non-rooted)
It has got a fragile algal like structure, grows to about 80 cms in length, roots are lacking, leaf branches are sometimes
modified into rhizoids, lower part of stem serves as an anchore and helps in the absorption of nutrients, leaves are set in
whorls, repeatedly forked with minute teeth on the side of the segment.
5. Cobamba (Fan wort)
Leaves are opposite, cut into thread like regions, stem slender with a gelatinous lining; plant provides shade and shelter
for small organisms and forms a beautiful aquarium plant.
iv. Emergent macrophytes
1. Nymphaea (Water lily / Nilkamal)
Found in ponds, lakes, canals and also in water up to 1.5 m depth, perennial herb, petiole with lower end of leaflet, leaf
round, veins radiating from the centre,leaves float on the surface of water,flower white or pink and solitary.
2. Nelumbo (Lotus)
Perennial herb, inhabiting tanks, ponds, lakes and other stagnant water bodies, leaves almost brown and are raised well
above the water surface when mature,petiole attached to the centre of leaf, veins prominently radiate from the centre,
flower large pinkish red leaf diameter ranging from 30 to 90 cms.
3. Trapa (Water chestnut / Singhara)
A perennial herb, occurs commonly in wild waters,leaves floating, solitary, branched or rhomboidal in shape, petiole
with spongy swelling, flowers are solitary projecting over water surface,nuts with two or four sharp spines.
4. Myriophyllum (Parrot head / Water milfoil)
Found in stagnant and slow moving waters especially in places which are sheltered from wind, plants with slender,
sparingly branched floating system mostly rooting freely at lower nodes, leaves opposite or whorled, the emergent
leaves are horn like, flowers are very small and sessile and found in the axis of upper, emergent leaves grows to
moderate height.
Other emergent type of plants are Nymphoides (Floating or Tringed water lily), Nuphar (Yellow lily or Cow lily) etc.

Limnology 2nd sem (full sylabus)

More Related Content

What's hot

Similar to Limnology 2nd sem (full sylabus)

More from SHUBHAM PATIDAR FISHERIES ADDAA

Recently uploaded

Limnology 2nd sem (full sylabus)