This presentation briefs the factors (physical) that may influence the lake ecology.

1. PHYSICAL AND
CHEMIOCAL
PROPERTIES OF LAKE
DR. SURJYA KUMAR SAIKIA
DEPARTMENT OF ZOOLOGY
VISVA-BHARATI

2. PHYSICAL PROPERTIES
TEMPERATURE
LIGHT
DEPTH
TURBIDITY
DISSOLVED SOLIDS

3. Lakes are extremely variable in their physical, chemical and
biological characteristics.
 Physical (level of light, temperature and water
currents)
 Chemical ( nutrients, major ions and
contaminants)
 Biological( biomass, population numbers and growth)
MAJOR FACTORS INFLUENCY LAKE BIOLOGY

6. PHYSICAL FEATURES
 TEMPERATURE
 WATER CONDITIONS
 DEPTH
 LIGHT
 TURBIDITYAND
 COLOUR

7. Primary role of light
- Plankton production – photosynthesis
(day)
- Respiration (night)
- Metabolism of the lake – controls the
ecosystem

8. Depending on light, lake is divided into two zones

9.  Autochthonous - energy
stored in photosynthetically
formed organic matter and
synthesised within the lake or
stream
 Allochthonous - energy stored
in photosynthetically formed
organic matter within drainage
basin and brought to the lake
or stream in various forms

10. ◦ Latitude
◦ Season
◦ Angle of contact of light rays at water surface
◦ Time of the day
◦ Degree of cloudiness or clearness of the sky, presence of
fog, smoke, dust or other atmospheric conditions.
◦ Dissolved ions – diminish light absorption. Traces of
ammonia, proteins and nitrates in solution still reduce
transparency of water to Ultraviolet light
◦ Suspended materials – composed of organic or inorganic
materials. They screen out the light (ex. Phytoplankton,
clay particles and abiotic materials)
◦ Presence of ice or snow cover – more light is reflected
Factor affecting penetration of light

11.  Light intensity at the lake surface
varies seasonally and with cloud
cover and decreases with depth
down the water column. The
deeper into the water column that
light can penetrate, the deeper
photosynthesis can occur.
 Photosynthetic organisms include
algae suspended in the water
(phytoplankton), algae attached to
surfaces (periphyton), and
vascular aquatic plants
(macrophytes).

12. Water is most dense at 4°C and becomes less
dense at both higher and lower temperatures.
Because of this density-temperature
relationship, many lakes in temperate climates
tend to stratify, that is, they separate into
distinct layers

13. Thermal Stratification – the presence of
different temperatures in a body of water

14. Stratification of water in a natural water body (lake).
Formation of horizontal water current and shearing plane in upper portion (epilimnion) is shown
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m

15. www.esf.edu

17. Turbidity
• Turbidity is a condition of water resulting
from the presence of suspended matters
• (1) Settling suspended matters
• (2) Non-settling suspended matters

18. Secchi disc, a metal painted black and white as shown attached to
graduated chainfor lowering in the water

19. Colours
of Lake
Blue water- water with
normal constituents
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Bright-green – water over
algae-covered depression
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Yellow - due to clayey
turbidity as well as also water
overlying a clean sandy area
Brown - abundance of diatoms
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Green- due to algal bloom
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Reddish-brown colour
of blooms of
dinoflagellate
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