Environment

1. Environment, Environmentalism, and Environmental science
The word Environment comes from the French verb ‘Environner’, means surroundings or something that
surrounds. It includes “all the conditions, circumstances, and influences surrounding and affecting an
organism or group of organisms”. Environment is taken to mean all those, which are physical and chemical,
organic and inorganic components of the atmosphere, lithosphere and oceans. Environment is the aggregate
of external conditions that influence the life of an individual or population, specially the life of men;
environment ultimately determines the quality and survival of life.
Environment - is anything immediately surrounding of an object and exerting a direct
influence on it. According to E.J. Ross - environment is an external force, which
influences us. Environment can be classified into three types as follows:
(i) Natural environment: It includes the natural things (air, water, mountain, sun, moon, etc.)
that are generally not influenced by means intelligence and powers.
(ii) Social environment: Man is always surrounded by society. This society remains with him from
birth to death.
(iii) Cultural environment: It includes social rules and regulations, traditions, customs, etc.
How the environment affects a culture (i.e. cultural dynamics):
1) Trade, 2) Food gathering, 3) Farming techniques, 4) Housing, 5) Communications/
transport, 6) Diet/nutrition, 7) Language (Eskimos have 50 words that categories
snow), and 8) Behavior/rationale.

2. SWE 534: Environmental Ecology 2 Credits/50 marks
Ecology and ecosystem. Soil as a habitat for organisms. Manipulation of soil ecology and soil
biotechnology.
Soil processes and properties involved in production of green house gases. Sources and sinks
of green house gases. Atmospheric chemistry of biogenic trace gases. Contribution of
terrestrial ecosystems to global climate change and vice versa. Global warming potential
(GWP) of greenhouse and anthropogenic gases, life time and CO2-equivalent.
Gas exchange and their impact on ecosystem.
Fluxes of carbon dioxide: emission from terrestrial ecosystems, effects of deforestation and
afforestation. Consequences of carbon dioxide emission.
Fluxes of Methane: Rice paddies and natural wetlands, methane consumption in terrestrial
ecosystem, factors regulation methane production.
Fluxes of nitrous oxide: Processes of nitrous oxide formation in soils, environmental and
agricultural control of nitrous oxide production, factors affecting nitrous oxide production,
emission of nitrous oxide from various ecosystems, Environmental consequences of
nitrification and denitrification.
Techniques for reducing greenhouse gases, C-sequestration. C-Sequestration potential in
different agricultural and forest ecosystems.
Types of general circulation models and their use in measurement of gas fluxes.

3. Main areas within society affected by the environment:
Cultural Ecologists argued that there were 4 main areas within
society which are particularly affected by the environment:
1) Division of labor - includes gender division of labor, age
division of labor, tasks done, if they are sedentary (sitting
much) or not.
2) Size and stability of people - includes food availability, size
of territory, type of territory.
3) Peoples’ distribution in space - includes availability of
food/water, vicinity to rivers, distance between groups (due
to conflict), and marriage rules.
4) Peoples’ residence rules - include gender division of labor,
female infanticide, and male domination.

4. Who, when wrote the book ‘Silent Spring’? What was its
impact on the society?
The late 20th century is known as the era of the modern environmental
movement. During this period, there was a significant increase in support
for the environment, which resulted in an increase in the number of laws
and policies established to help protect the environment. One of the most
influential events of the late 20th century was the publication of the
book Silent Spring by Rachel Carson in 1962.
In this book, Carson discussed the effects of pesticides and herbicides on
the environment, opening the public's eyes to the ways in which we are
harming our own environment. Carson's book caught the attention of the
Former US President John F. Kennedy and led to the formation of two
acts: the Environmental Policy Act 1964, which was the first legislation
that acknowledges a connection between human actions and
environmental systems, and the Wilderness Act of 1964, which
designated over 100 million acres of wilderness and gave the land the
highest level of protection.

5. Environmentalism - is a popular movement with political, social and
philosophical implications. Environmentalism is like "The Green Movement". It is a
social movement, which involves people who are environmentally concerned coming
together with certain ideas and who become activists. It protects the environment,
makes others aware of environmental issues, and reduces deforestation, the extinction
of species, the loss of habitats and indigenous knowledge. Environmentalism is
concerned with both our own society, and those of SSS (Small Scale Societies).
Environmental Science
Environmental science is the field of science that studies the interactions of the
physical, chemical, and biological components of the environment and also the
relationships and effects of these components with the organisms in the environment.
Environmental Science is the study of natural cycles and systems and their components.
It provides a means for obtaining precise information about the environment for better
understanding. Environmental science comprises those disciplines or parts of them,
which consider the physical, chemical and biological aspect of the environment. Any
study of the earth and the life it supports must deal with process and change. The earth
science and life science also deal with process and change, but environmental science is
especially concerned with change brought by human activities and their immediate and
long-term implications for the welfare of living organisms, including humans.

6. Goals of environmental science
The field of environmental science can be divided into three main goals, which are (i)
to learn how the natural world works, (ii) to understand how we as humans
interact with the environment, and also (iii) to determine how we affect the
environment. The third goal of determining how humans affect the environment also
includes finding ways to deal with these effects on the environment.
Interdisciplinary Field
Environmental science is also referred to as an interdisciplinary field because it
incorporates information and ideas from multiple disciplines. Within the natural
sciences, such fields as biology, chemistry, and geology are included in environmental
science. When most people think of environmental science, they think of these natural
science aspects, but what makes environmental science such a complex and broad
field is that it also includes fields from the social sciences and the humanities.
The social science fields that are incorporated into environmental science include
geography, economics, and political science. Philosophy and ethics are the two fields
within the humanities that are also included in environmental science. By combining
aspects of the natural sciences, social sciences, and the humanities, the field of
environmental science can cover more concepts and also examine problems and topics
from many different points of view.

7. What is Ecology?
A German scientist named Ernest Haeckel in 1869 first used the word ecology. It
comes from two Greek word oikos meaning home and logos meaning understanding.
Haeckel described ecology as ‘the domestic side of organic life’ and ‘the knowledge of
the sum of the relations of organisms to the surrounding outer world, to organic and
inorganic conditions of existence’. This ‘surrounding outer world’ is another way of
saying the environment. More precisely Haeckel defined ecology as “the
comprehensive science of the relationship of the organism to the environment”.
Ecology is the study of organisms in relation to the surroundings in which they
live. These surroundings are called the environment of the organism. Some other
scientists defined ecology in the following ways:
* Ecology is the science of the community (Frederick Clements, 1916).
* Ecology is the science of all the relations of all the organisms to their entire
environment (Trailor, 1936).
* Ecology is the study of interrelations of plants & animals with their environment
(Clarke,1954).
* Ecology is the scientific study of the structure and functions of nature (Odum, 1963).
* Ecology, in a broad sense, is the study of ecosystems (Misra, 1970).
* More recently Krebs (1985) has defined ecology as ‘the scientific study of the
interactions that determine the distribution and abundance of organisms’.
Khan, H.R. (2000) defined it as ‘Ecology is the science of relationships of an object
with its surroundings’.

8. Aims of an Ecologist:
Ecologists, those, who study ecology, are always aiming to understand how an
organism fits into its environment. The environment is of supreme importance to an
organism and its ability to exist in the environment where it lives will determine its
success or failure as an individual.
What are the main approaches to study ecology?
The only way to find out how any organism survives, reproduces and interacts with
other organisms is to study it. This makes ecology a practical science. There are three
main approaches to the study of ecology.
(1) The simplest method is to observe and record the organism in its natural
environment. This is sometimes described as observation ‘in the field’ or fieldwork.
(2) A second type of study is to carry out experiments in the field to find out how the
organism reacts to certain changes in its surroundings.
(3) The third approach involves bringing organisms into a controlled environment in a
laboratory, cage or greenhouse.
This experimental aspect can be very useful, as it is often easier to record information
accurately under controlled conditions. However, it must be remembered that the
organisms may react differently because they have been removed from their natural
home.
No single study can hope to discover everything there is to know about the relationships
between an organism and its environment. These relationships are so varied that
different kinds of investigation are needed to study them.

9. Ecosystem:
Living organisms and their environments together make up an
ecosystem, as patterned arrangement of exchanges and energy flows. A
habitat and the community contain single working systems. Organisms
and their physical environment are therefore interacting parts of a
system. The term ecosystem is now used to describe such a system. An
ecosystem is a small segment of nature embracing communities of living
things and their physical environments. An ecosystem is a discrete
structural, functional and life sustaining environmental system.
The basic and most important concept of an ecosystem is that everything
is somehow related to everything else in nature.
Major types of ecosystems are -
Soils, 2. Wetland and aquatic ecosystems (Water - lake pond, Types of
wetlands: Sea, Stream & River, Groundwater and rain & snow),
3. Marine wetland (mangrove swamps and salt marshes),
4. Flood land ecosystems, 5. Swamp and Marsh ecosystems, 6. Bog
ecosystems, and 7. Aquatic ecosystems.

10. Some technical terms regarding Environment:
TDS (Total dissolved solids or salts), TSS (Total suspended solids),
Total Hardness (Ca + Mg), Total Alkalinity (Total carbonate + bicarbonate),
PM10 & PM2.5 (Particulate mater of 10 and 2.5 micron or micro-meter in size),
SPM (Suspended Particulate Matter), ppmv (parts per million by volume), etc.
NOx (Oxides of nitrogen), DOC (Dissolve organic carbon),
CBOD (Carbonaceous Biological Oxygen Demand),
NBOD (Nitrogenous Biological Oxygen Demand),
IPCC (Intergovernmental Panel on Climate Change
HFCs (Hydrofluorocarbons), PFCs (Perfluorocarbons), and SF6 (sulfur hexafluoride)
Dissolved Oxygen (DO): Oxygen dissolved in water has been an important vital
species, which gets consumed by oxidation of organic matter/reducing agent. It is
regarded as an important water quality parameter. Its optimum value for good quality
water has been 4 to 6 mg L-1 of dissolved oxygen (DO), which is able to maintain
aquatic life in a water body. If DO values are somewhat lower than this value, this
indicates water pollution.
Biological Oxygen Demand (BOD): Oxygen demand by aquatic lives is usually
referred to as BOD.
Chemical Oxygen Demand (COD): Oxygen required for the oxidation of chemical
compounds or elements is referred to as COD. In normal water, the value of COD will

11. What is meant by the diversity- stability- hypotheses?
The relative stability of many ecosystems, although measurable, is difficult to explain. Particularly in
sixties ecologists have hallowed the diversity-stability-hypotheses which basically states that
increasing diversity causes increasing stability. This hypothesis appears to be supported by the
stability of two of the most species-rich ecosystem types of the world are tropical rainforests and coral
reefs.
Food Webs:
A food web consists of many food chains. A food chain only follows just one path as animals
find food. eg: A hawk eats a snake, which has eaten a frog, which has eaten a grasshopper, which has
eaten grass. A food web shows the many different paths plants and animals are connected.
Food Webs: A food web summarizes the feeding relations in a community.
All organisms have a community and ecological role. The chief roles are (Fig.):
1. Producers (autotrophs) - algae, plants, photosynthetic bacteria, etc.
2. Consumers (heterotrophs) – herbivores, carnivores and top carnivores.
3. Decomposers (microconsumers or saprophages).
Gross primary production is the amount of material synthesized by autotrophs per unit time.
The organisms which feed on the (net) primary production are known as heterotrophs or
consumers. The energy stored in consumers is called secondary production.
Decomposers or saprophages feed on waste products and dead tissues.
An ecosystem contains two chief types of food web:
(i) a grazing food web (plants, herbivores, carnivores, top carnivores) and (ii) a decomposer
or detritus food web.

12. How is a food chain related to a food web?
Food webs, on the other hand, show how several food chains are related. It is a more complex
depiction of how the plants and animals in an ecosystem relate. A food web may begin with prairie
grass, which would be eaten by insects, mice or rabbits, which would be eaten by different predators
(Mar 13, 2018).
How do food webs work?
A food chain describes how energy and nutrients move through an ecosystem. At the basic level there
are plants that produce the energy, then it moves up to higher-level organisms like herbivores. In
the food chain, energy is transferred from one living organism through another in the form of food.
What is an example of the food chain?
Food chain refers to the sequence of events in an ecosystem, where one organism eats another and
then is eaten by another organism. It starts with the primary source like the sun or hydrothermal vents
where producers make food, continues with consumers or animals that eat the food, and ends with the
top predator.
How does a food web differ from a food chain?
A food web consists of many food chains. A food chain only follows just one path as animals
find food. eg: A hawk eats a snake, which has eaten a frog, which has eaten a grasshopper, which has
eaten grass. A food web shows the many different paths plants and animals are connected.
What is the 10% rule in the food chain?
The 10% Rule means that when energy is passed in an ecosystem from one trophic level to the next,
only ten percent of the energy will be passed on. A trophic level is the position of an organism in
a food chain or energy pyramid.

13. WhatIsBiodiversity?
Did you know there are more than 10,000 species of birds, 200,000 species of flowering plants and
almost one million species of insects in the world? The number of species identified has increased
substantially in recent years, and there are over 1.5 million species currently known. Although this
number might seem large, it is thought that this number is actually only a fraction of the number of
species that exist today. New species are being identified every day, and it is estimated that there are
anywherebetweenthreeandfiftymilliondifferentspecieslivingonEarth.
When discussing the number of species on earth, the term biodiversity is often
mentioned.Biodiversity, also known as biological diversity, is the variety of life on Earth across all
of the different levels of biological organization. On a smaller scale, biodiversity can be used to
describe the variety in the genetic makeup of a species, and on a larger scale, it can be used to
describethevarietyofecosystemtypes.

14. Types of Biodiversity
Biodiversity is a very broad term and is often divided into three types. The first type of biodiversity is
species diversity, and this is the type of biodiversity most people are familiar with. Species
diversity is defined as the number and abundance of different species that occupy a location. To
accurately determine species diversity, both the species richness, which is the number of different
species, and the relative abundance, which is the number of individuals within each species, must be
considered. An example of species diversity would be the number and abundance of different types of
mammals in a forest.
The second type of biodiversity is genetic diversity. Genetic diversity is the amount of variation in
genetic material within a species or within a population. There is a high level of diversity among
species, but there is an even higher level of diversity among the genetic material of the individuals of
a specific species. An example of genetic diversity is the variation in the genes that encode for hair
color in humans.
The third type of biodiversity is ecological diversity, and this is the variation in the ecosystems found
in a region or the variation in ecosystems over the whole planet. Ecological diversity includes the
variation in both terrestrial and aquatic ecosystems. Ecological diversity can also take into account the
variation in the complexity of a biological community, including the number of different niches, the
number of trophic levels and other ecological processes. An example of ecological diversity on a
global scale would be the variation in ecosystems, such as deserts, forests, grasslands, wetlands and
oceans. Ecological diversity is the largest scale of biodiversity, and within each ecosystem, there is a
great deal of both species and genetic diversity.

15. #Whatarethebasicconceptsofbiodiversity?(P.118,BotkinEnv.Sci)
Biodiversityraisesthreeconcepts.
Generic Diversity: Generic diversity refers to the mixture and the range of genes, i.e. the total
numberofgeneticcharacteristics,sometimesofaspecificspecies,suspicious,orgroupofspecies.
Habitatdiversity:Thediversityofhabitatsinagivenunitarea.
Speciesdiversity:Meansthevarietyofdifferingwildlifespecies.Ithasthreeaspects:(a)Species
richness the total no. of species; (b) Species evenness the relative abundance of species; (c) Sp.
dominancethemostabundantSpecies.

16. What is being done to help conserve the biodiversity and endangered species?
(Ref. Env. Sci. Botkin p. 246)
We candoagreatdeal tohelpconserve biological diversityandendangeredspecies by:
1. takingemergencyactionsfor seriouslyendangeredspecies;
2. determiningtheminimumviablepopulationsizefor aspecies;
3. assistingaspeciesinachievingthatsize,includingartificial breedinginzoosandgardens;
4. determiningthecharacteristics of aminimumviablehabitat andecosystemforaspecies;
5. restoringadamagedhabitatandecosystemor creatinganewhabitatappropriatefor thespecies;
6. takinganecosystemapproachtoconservation;
7. understanding and applying the concept of an ecological island and acting to overcome the
limitationsof suchislands;
8. monitoringthepopulationanditshabitat andecosystemto maintaininformationabout trendsand
conditions; and
9. developing better means to project future population levels using mathematical models and
computer simulation.

17. Briefly describe some major factors which increase and decrease the biodiversity
A. Factors that tend to increase diversity
1. A physically diverse habitat
2. Moderate amounts of disturbance (such as fire or storm in a forest of a
sudden flow of water [from a storm] into a pond)
3. A small variation in environmental conditions (temperature,
precipitation, nutrient supply, etc.)
4. High diversity at one trophic level, increasing the diversity at another
trophic level (many kinds of trees provide habitats for many kinds of
birds and insects)
5. An environment highly modified by life (e.g., a rich organic soil)
6. Middle stages of succession
7. Evolution
B. Factors that tend to decrease diversity:
1. Environmental stress
2. Extreme environments (conditions near to the limit of what living thing
can withstand)
3. A severe limitation in the supply of an essential resource
4. Extreme amounts of disturbance
5. Recent introduction of exotic species (species from other areas)
6. Geographic isolation (being on a real or ecological island)

18. Environmental Quality Standard (EQS)
A ‘Standard’ constitutes a prescribed limit, which, in the case of environmental
pollution, is the permissible discharge of pollutants into the media, such as air, water
and land, which in turn, sets the environmental quality criteria. These are essential for
managing the environment. These standards to be effective as a management tool must
be in consistent with the implementation capabilities of each country. Increasingly,
standards are prescribed by the governmental authorities following consultations with
relevant stakeholders, including the private sector; to ensure an incremental advance
towards higher standards of environmental quality.
Control mechanisms are those that are employed to enforce the prescribed
environmental standards and realize the agreed environmental criteria. Licenses and
permits are used for this purpose. For large projects that are likely to cause significant
harm to the environment, an Environmental Impact Assessment is used. Guidelines are
designed to assist parties to follow the prescribed conduct, and thus provide a basis for
ensuring both, certainty with regard to specifics, and consistency.

19. Standards for Water (Environmental Procedures & Guidelines, 1999)
(A) Standards for inland surface water
Best Practice based classification pH
BOD
(mg/l)
DO
(mg/l)
Total Coliform
(number/100 ml)
a. Source of drinking water for supply
only after disinfecting:
6.5-8.5 2 or less 6 or above 50 or less
b. Water usable for recreational activity:
6.5-8.5 3 or less 5 or more 200 or less
c. Source of drinking water for supply
after conventional treatment:
6.5-8.5 6 or less 6 or more 5000 or less
d. Water usable by fisheries: 6.5-8.5 6 or less 5 or more ---
e. Water usable by various process and
cooling industries:
6.5-8.5 10 or less 5 or more 5000 or less
f. Water usable for irrigation: 6.5-8.5 10 or less 5 or more 1000 or less
Notes:
1. In water used for pisciculture, maximum limit of presence of ammonia as Nitrogen is 1.2 mg/l.
2. Electrical conductivity for irrigation water –2250 μS/cm (at a temperature of 25˚C); Sodium less than 2.6%; boron less
than 0.2%.

20. Sl.
No.
Parameter Unit Standards
1 Aluminum mg/l 0.2
2 Ammonia (NH3) mg/l 0.5
3 Arsenic mg/l 0.05
4 Barium mg/l 0.01
5. 13. Chlorine (residual) mg/l 0.2
6. 14. Chloroform mg/l 0.09
7. 15. Chromium (hexavalent) mg/l 0.05
8. 16. Chromium (total) mg/l 0.05
9. 17. COD mg/l 4
10. 18. Coliform (fecal) n/100 ml 0
11. 19. Coliform (total) n/100 ml 0
12. 20. Color Hazen unit 15
13. 21. Copper mg/l 1
14. 22. Cyanide mg/l 0.1
(B) Standards for drinking water

21. Comparison of environmental regulations for textile industries (Old data, i.e. before 1996)
Parameters Germany Indonesia Japan Venezuela India Bangladesh
pH 6.6-8.5 6-9 5.8-8.6 6-9 5.5-9.0 6.5-9.0
BOD5 (mg/l) 40 85 30-120 60
100-
150
150
COD (mg/l) 280 250 30-120 350 - 400
Suspended solid
(mg/l)
40 60 200 60 100 100
Oil & Grease
(mg/l)
- 5 5-35 20 - 10
Phenol (mg/l) - 1 5 0.5 5 5
Chromium (mg/l) 2 2 2 2 2 2
Parameter standard mainly dependent on receptor’s condition and different country has different kind of receptor. So, these parameter standards
vary from country to country.
Are these Standards static?
No, these standards are not static because in the regulations, there is no point mentioned about the validity of the discharged standard set for the
ambient and industrial conditions. The Envi. Quality Standard (EQS) have been subjected to change in many countries over period of time.

22. Biogeography: It refers to the large scale geographic pattern in the distribution of
species, and the causes and history of this distribution.
The kinds of species as well as the number vary greatly from place to place on earth. If
we are interested in conserving biological diversity, it is important that we understand
these large scales, global patterns, which we refer to as patterns in biogeography.
Knowledge on biogeography helps us to predict what will grow where based on climate
similarity- has been used for major economic benefits.
Major global patterns in the distribution of species have long been recognized. Aristotle
recorded some of the first principles of biogeography; he distinguished boreal,
temperate and tropical life zones. During the nineteenth century, global patterns
becomes a subject of scientific study, partly because of explorations of new world
tropics, South America, the south pacific, Australia and parts of Asia.
Biomes: A biome is a regional community of animals and plants. Another way of
looking at biome means the biogeography of earth is in terms of similarity of
environment. Similar environment lead to the evolution of organisms, similar in form
and function (but not necessarily in genetic heritage or internal makeup) and similar
ecosystems. This is known as the rule of climate similarity and lead to the concept of
biome. A biome is a kind of ecosystem, such as a desert, tropical rain forest, or
grassland. For example, rain forests occur in many parts of the world but are not all
connected with each other. Biome is also defined as a biological community and the
environmental conditions that characterize it. Assemblies of organisms living in
generally similar surroundings over a large geographic area constitute a biome.

23. 10. Intertidal biomes: The intertidal biomes are made up of area exposed alternately to
air during low tide and ocean water during high tide. Constant movement of water
transports nutrient into and out of these area, which are usually rich in life and are major
economic resources.
11.Open Ocean: Open water of much of the Oceans. These vast areas tend to be low in
N and P, which is known as chemical deserts with low diversity of algae.
12. Benthos: Benthos (deep) is the bottom portion of Ocean. Primary input of food is
dead organic matter that fully from above; water is too dark for photosynthesis, so no
plant grows there.
13. Upwelling: Deep ocean water is nutrient rich because of numerous creatures who
die in surface water and sink. Upward flow or upwelling of deep ocean waters brings
nutrient to the surface, allowing abundant growth of algae and animals that depends on
algae. Upwelling is important for the production of commercial fish.
14. Hydrothermal vents: This recently discovered biomes occur in deep Ocean, where
tectonic (geologic) process creates vents of hot water with a high concentration of S-
compounds. These compounds provide an energy basis for chemistry, bacteria which
support giant clams, worms and other unusual life form. Water pressure is high and
temperature ranges from boiling water at the top of the vents to the frigid (above 4ºC)
water at deep Ocean.

24. Life at low temperatures
The greater part of our planet is cold (below 5°C) and ‘cold is the
fiercest and most widespread enemy of life on earth’ (Franks et al.,
1990). More than 70% of the planet is covered with sea water: mostly
Deep Ocean with a remarkably constant temperature of about 2°C. If we
include the polar ice-caps, more than 80% of earth’s biosphere is
permanently cold. We inhabit a cold planet, and should perhaps regard
those organisms that are best able to cope with low temperatures as being
its most successful colonizers (Russell, 1990).
By definition, all temperature below the optimum are harmful but
there is usually a wide range of such temperatures that cause no physical
damage and over which any effects are fully reversible. There are,
however, two quite distinct types of damage at low temperatures (chilling
and freezing), that can be lethal either to tissues or to whole organisms.

25. Injury from chilling
Cold itself can have physical and chemical consequences even though ice
may not be formed. Water may supercool to temperatures at least as low
as – 40°C, which changes its viscosity (increases), diffusion rate
(decreases). Over the range from 25 to –25°C the degree of ionization of
water decreases nearly 100-fold, and as hydrogen ions (H+) and hydroxyl
ions (OH+) are involved in almost all biological processes. Many
organisms are damaged by exposure to temperatures that are low, but
above freezing point – so-called ‘chilling injury’. Many species of
tropical rainforest are sensitive to chilling. The nature of the injury is
associated with the breakdown of membrane permeability and the
leakage of specific ions such as calcium (Minorski, 1985). Organisms are
said to be ‘chill tolerant’ when they survive temperatures that are
suboptimal but are never low enough for freezing to occur. Chilling
injury and tolerance (like the response to super cooling) are quite
different from injury by and tolerance to the formation of ice, i.e.
freezing.

26. Injury from freezing
Ice seldom forms in an organism until the temperature has fallen several degrees
below 0°C – it remains in a super cooled state until it solidifies suddenly around
particles that act as nuclei. When ice forms in plant or animal tissues it is almost always
extracellular water that freezes. It is very rare for ice to form within cells and it is then
inevitably lethal, but the freezing of extracellular water is one of the factors that prevent
ice forming within the cells themselves (Franks et al., 1990). As extracellular ice forms,
water is withdrawn from the cell, and solutes in the cytoplasm (and vacuoles) become
more concentrated. The effects of freezing are therefore mainly osmoregulatory: the
water balance of the cells is upset and cell membranes are destabilized. The effects are
essentially similar to those of drought and salinity. Extreme water withdrawal from
plant cells destroys the semi-permeability of the plasma membranes and may even
cause the physical tearing of the cytoplasm away from the cell walls.
The risk of damage from freezing is greatest if super cooling has occurred and ice
forms suddenly – it is then that there is the greatest chance that lethal intracellular ice
will form. Certain bacteria (Pseudomonas syringae and Erwinia herbicola) are able to
synthesize materials that catalyse the formation of ice at temperatures as high as – 4°C
(Schnell & Vali, 1976). Some species of bivalves and gastropods also produce ice-
nucleating protein that induce the formation of extracellular ice during the winter
(Johnston, 1990). Cont’d……..

27. Con’td……
When extracellular ice is formed, the withdrawal of water from the
cells is resisted by the accumulated osmotically active molecules and
ions. In addition, much of the ability of both plants and animals to
tolerate freezing temperatures (and drought and salinity), appears to
depend on antifreezes. For example, the blood of the fish, Pagothenia
borchgrevinki, from McMurdo Sound, Antarctica, has a freezing point
of –2.7°C compared with –0.8°C for a comparable but more typical
marine fish, and this is due partly to a higher concentration of sodium
chloride and partly to peptides and large glycopeptides which depress
the freezing point 200-300 times more than expected from their
concentration. Such compounds are particularly important in the
process of ‘frost hardening’ by which organisms acquire a tolerance of
low temperatures.

28. Acclimation to life at low temperatures
Perhaps what is most striking about the tolerances of organisms to
low temperatures is that they are not fixed but are preconditioned by the
experience of temperatures in their recent past. This process is called
acclimation when it occurs in laboratory and acclimatization when it
occurs naturally. The exposure of an individual for several days to a
relatively low temperature can shift its whole temperature response
downwards along the temperature scale. Similarly, exposure to a high
temperature can shift the temperature response upwards.
In higher plants the development of cold tolerance is triggered by
environmental cues. Most commonly a period of 4–6 weeks at
temperatures of 0–5°C, usually accompanied by decreasing day length
(photoperiod), provides the stimulus for acclimatization.

29. Soil Biotechnology
In recent years, a greater understanding of soil ecology has facilitated the
emergence of a soil biotechnological revolution where biological
components (plants, microbes and animals) of the soil/plant system are
manipulated to increase plant (i.e. crop) productivity. These
manipulations are increasingly involving genetic change although many
can simply involve the selective introduction, control or removal of soil
organisms. The first microbial inoculum to be introduced into agricultural
systems as a biofertilizer was almost certainly Rhizobium, the controlled
use of rhizobial inocula dating back to the late nineteenth century.
Biofertilization by Rhizobial Inoculation
In tropical agriculture, the potential for improved crop productivity from
rhizobial inoculation is generally much higher than for temperate
systems. Crops such as soybeans (Glycine max.), peanuts (Arachis
hypogea) and mung beans (Vigna radiata) are good examples of tropical
legumes that can benefit enormously from rhizobial inoculation.

30. When will inoculation be most effective?
In general, inoculation will be most effective when the soil’s indigenous rhizobia are
either ineffective or present in insufficient numbers to provide a reasonable inoculum.
An extreme case of this latter problem can be found in Australia where native
populations of rhizobia are often completely absent. Similar situations may also exist
when previously barren soils, such as in arid areas, are brought into cultivation. These
types of situation contrast sharply with temperate agricultural soils, which can have an
indigenous rhizobial population of about one hundred thousand per gram.
Common methods of inoculum introduction
For large legume seeds such as those of soybean, inocula are only really effective with
about 1 million viable cells per seed. Sometimes single strain inocula are used, whereas
sometimes multiple strains are preferred. The latter tends to be more effective over a
broader range of crop and soil conditions. The most common method of inoculum
introduction is to incorporate the rhizobial cells with a carrier that can act as a sort of
coating for the legume seeds as they are sown. This coating may often be peat, clay, or
peat-charcoal based, and enables both prolonged survival of the inoculum (both in
storage and in the field) and close contact between legume seed and inoculum.
Sometimes, the carrier is stuck to the seed with gum aerobic or similar resinous
compounds as a true seed coating, sometimes applied in granules, and sometimes
sprayed into the seed furrow as a slurry suspension. Crop response to these rhizobial
inoculation procedures is greatest when the soil is first planted with a particular legume.

31. Factors affecting inoculums success
Factors affecting inoculums success include considerations at all stages
of inoculum use – strain selection, culturing of the strain, carrier
preparation, mixing of the culture and carrier, maturation, storage,
transport and application. A key factor in the success of a rhizobial
inoculum will be the level of moisture at which the cells are maintained.
The peat or clay rhizobial carrier must remain moist prior to sowing.
After sowing, the water potential regime of the recipient soil will be a
fundamental factor in determining inoculum success. Other important
factors determining inoculum success include soil temperature, diffusates
from legumes and/or other higher plants, microbial antagonism,
bacteriophage activity, microbial parasitism and protozoan predation
(Natman, 1971).

32. Factors affecting the success of a microbial inoculum in soil.
In many soils, acidity will also play an important part in determining the survival and
success of an inoculum. In acid soils, it is generally the high availability of aluminum
that provides the biggest problem for the soil biota. Reduced by 50 µM aluminum at pH
4.5. More relevant, however, is to study the effect of aluminum and acidity when the
rhizobia are in the presence of the host legume (Andrew, 1978). This approach shows
that pH 4.3 can cause death of a rhizosphere population of R. trifolii but does not affect
root elongation or root hair formation of white clover (Trifolium repens: Wood, Cooper
and Holding, 1983). Many legumes, therefore, may not be nodulated by rhizobia in acid
soils, largely the result of the high susceptibility of rhizobia in acid soils, largely the
result of the high susceptibility of rhizobia to aluminum.
Successful inoculation of a legume may be hampered because of the poor nutrition of
the legume itself. Legumes tend to have restricted root systems and are poor nutrient for
agars. This is particularly true for phosphorus, which is deficient in most tropical soils.
Improved inoculation will often result from either additions of phosphate fertilizer or
from VAM (vesi-cular arbascular micorrhiza) infection. Once VAM fungal inocula can
be effectively produced, perhaps a combined VAM/rhizobial inoculum will be most
effective for tropical legumes.
Cont’d…

33. Cont’d….
The soil factors that influence the survival and success of rhizobial inocula are not
likely to act independently. For example, there is a strong interaction between soil
moisture status and soil temperature (Danso and Alexander, 1975) and the clay content
of the soil environment modifies the strength of this interaction.
Factors affecting the success of a microbial inoculum in soil are shown by the following flowchart.
Method of inoculum
production, storage
and introduction
Soil chemical factors -
pH, avail. nutrients,
pesticides, redox
Soil physical factors -
water potential,
temperature, clay,
etc.
Vegetations factors - host
specificities, diffusates,
rhizosphere effects
SUCCESS OFA
MICROBIAL
INOCULATION
Climatic factors -
Seasonal, Freezing,
Thawing
Effects of viruses
particularly
bacteriophage
Interactions with soil
animals- Protozoan
predation, dispersal
Competition from
indigenous soil
microbes

34. Potential benefits of mycorrhizal fungal inoculation
The potential benefits of mycorrhizal fungal inoculation for
biofertilizing arable and forest crops are very considerable.
These benefits to the plant host range from enhanced nutrient
uptake, through increased tolerance of the host to
environmental stresses such as soil water stress and heavy-
metal toxicity, enhanced resistance to many of the soil-borne
pathogenic microbes.
With a trend towards less intensive agriculture in the UK and
much of Europe, the associated application of lower levels of
fertilizers and pesticides should increase the importance of
mycorrhizal associations of crops, both in terms of
enhancing crop nutrient uptake from soil, and also of
combating

35. Genetically modified plants and microbes for use in the environment
Genetic modification of plants to improve crop yields and increase
efficiency of agriculture represents one of the most rapidly developing
areas of biotechnology. Great advances have been made with regard to
modification of crop plants to enhance resistance to pests such as fungi,
viruses and insects (Primrose, 1991) as well as to the chemicals
(pesticides) currently used to control these pests (Gasser and Fraley,
1992). Ultimately, it may be possible to carry out genetic modifications
to the photosynthetic mechanisms of plants to enable more efficient
fixation of atmospheric carbon dioxide and hence increase the potential
of agriculture for primary production (Lindsey and Jones, 1989).
As more potential is identified for the use (agricultural and otherwise) of
microbial inocula in soils, so too will increase the possibility of refining
these systems (and developing new systems) through the use of genetic
engineering. Even genetically modified viruses may be used in pest
control in crop and tree production.

36. Soil ecological effects of the use of genetically modified plants and microbes
The biotechnological development and use of genetically modified plants and microbes
although offering a wide range of potential benefits which must be assessed (usually in
contained trials) before any environmental introduction can be made.
Assessment of the ecological effects of modified plants and microbes should include – 1.
monitoring of competition (persistence and invasion of indigenous communities), 2.
pathogenicity and toxicity (to non-target organisms), 3. gene transfer (to indigenous
organisms) and 4. dispersal (beyond the intended target environment). The techniques
required to do this for plants are much better established than for microbes and
additionally, 5. assessment of the soil ecological effects of GMM’s necessitates sensitive
detection in the soil environment.
Detection and monitoring of GMM’s in soil involves a range of both extractive and in situ
techniques, as well as development of new techniques with improved power and sensitivity.
Ideally, techniques are needed that can detect single cells in situ, assay their activity, and
facilitate genomic tracking. One such technique involves the cloning of flux genes for
bioluminescence from marine vibrios into the selected soil inoculum (Grant et al., 1991).
Because there is little or no background of bioluminescence (production & emission of light by living
organisms), cells can be imaged with the degree of bioluminescence (catalyzed by the enzyme
luciferase) proportional to their metabolic activity. The bioluminescence marker system has
the additional advantage that it does not give rise to the environmental concerns associated
with antibiotic resistance markers.

37. Phytoremediation:
Phytoremediation is a new technology that uses specially selected metal
accumulating plants to remediate soil contaminated with heavy metals and
radionuclides. Phytoremediation offers an attractive and economical alternative to
currently practiced soil removal and burial methods. The integration of specially
selected metal accumulating crop plants (e.g., Brassica juncea) with innovative soil
amendments allows plants to achieve high biomass and metal accumulation rates
from soils.
The use of plants to remove toxic metals from soils (phytoremediation) is being
developed as a method for cost-effective and environmentally sounds remediation
of contaminated soils. Metal (hyper) accumulating plants have been required that
have the ability to accumulate and tolerate unusually high concentrations of heavy
metals in their tissue. Accumulators of Ni, Zn, for example, may contain as much
as 5% of these metals on a dry-basis weight. This process of extracting metals from
the soil and accumulating and concentrating metals in the aboveground plant
tissues enables plants to be used as part of a soil cleanup technology.
Phytoremediation is a modern technology that uses metal accumulating plants to
remediate contaminated soil and water.
Phytoextruction:

38. Phytoextraction is a sub-process of phytoremediation in which plants remove dangerous
elements or compounds from soil or water, most usually heavy metals, metals that have a high
density and may be toxic to organisms even at relatively low concentrations.[1] The heavy metals
that plants extract are toxic to the plants as well, and the plants used for phytoextraction are
known hyperaccumulators that sequester extremely large amounts of heavy metals in their
tissues. Phytoextraction can also be performed by plants that uptake lower levels of pollutants,
but due to their high growth rate and biomass production, may remove a considerable amount of
contaminants from the soil.[2]
Heavy metals can be a major problem for any biological organism as they may be reactive with a
number of chemicals essential to biological processes.
They can also break apart other molecules into even more reactive species (such as: Reactive
Oxygen Species), which also disrupt biological processes. These reactions deplete the
concentration of important molecules and also produce dangerously reactive molecules such as
the radicals O. and OH..
Non-hyperaccumulators also absorb some concentration of heavy metals, as many heavy metals
are chemically similar to other metals that are essential to the plants life.
The process:
For a plant to extract a heavy metal from water or soil, five things need to happen.
1. The metal must dissolve in something the plant roots can absorb.
2. The plant roots must absorb the heavy metal.
3. The plant must chelate the metal to both protect itself and make the metal more mobile (this
can also happen before the metal is absorbed). Chelation is a process by which a metal is
surrounded and chemically bonded to an organic compound.
4. The plant moves the chelated metal to a place to safely store it; and
5. Finally, the plant must adapt to any damages the metals cause during transportation & storage.

39. Dissolution
In their normal states, metals cannot be taken into any organism. They must be dissolved as
an ion in solution to be mobile in an organism.[3] Once the metal is mobile, it can either be
directly transported over the root cell wall by a specific metal transporter or carried over
by a specific agent. The plant roots mediate this process by secreting things that will capture
the metal in the rhizosphere and then transport the metal over the cell wall. Some examples
are: phytosiderophores, organic acids, or carboxylates[4] If the metal is chelated at this
point, then the plant does not need to chelate it later and the chelater serves as a case to
conceal the metal from the rest of the plant. This is a way that a hyper-accumulator can
protect itself from the toxic effects of poisonous metals.
Root absorption: The first thing that happens when a metal is absorbed is it binds to the
root cell wall.[5] The metal is then transported into the root. Some plants then store the
metal through chelation or sequestration. Many specific transition metal ligands
contributing to metal detoxification and transport are up-regulated in plants when metals
are available in the rhizosphere.[6] At this point the metal can be alone or already
sequestered by a chelating agent or other compound. To get to the xylem, the metal must
then pass through the root symplasm.
Root-to-shoot transport: The systems that transport and store heavy metals are the most
critical systems in a hyper-accumulator because the heavy metals will damage the plant
before they are stored. The root-to-shoot transport of heavy metals is strongly regulated by
gene expression. The genes that code for metal transport systems in plants have been
identified. These genes are expressed in both hyper-accumulating and non-hyper-
accumulating plants.

40. There is a large body of evidence that genes known to code for the transport systems of heavy metals
are constantly over-expressed in hyper-accumulating plants when they are exposed to heavy
metals.[7] This genetic evidence suggests that hyper-accumulators overdevelop their metal transport
systems. This may be to speed up the root-to-shoot process limiting the amount of time the metal is
exposed to the plant systems before it is stored. Cadmium accumulation has been reviewed.[8]
These transporters are known as heavy metal transporting ATPases (HMAs).[9] One of the most well-
documented HMAs is HMA4, which belongs to the Zn/Co/Cd/Pb HMA subclass and is localized at
xylem parenchyma plasma membranes.[10] HMA4 is upregulated when plants are exposed to high levels
of Cd and Zn, but it is down regulated in its non-hyperaccumulating relatives.[11] Also, when the
expression of HMA4 is increased there is a correlated increase in the expression of genes belonging to
the ZIP (Zinc regulated transporter Iron regulated transporter Proteins) family. This suggests that the
root-to-shoot transport system acts as a driving force of the hyper-accumulation by creating a metal
deficiency response in roots.[12]
Storage Systems that transport and store heavy metals are the most critical systems in a hyper-
accumulator, because heavy metals damage the plant before they are stored. Often in hyper
accumulaters the heavy metals are stored in the leaves.
How phytoextraction can be useful For Plants
There are several theories to explain why it would be beneficial for a plant to do this.
The "elemental defence" hypothesis assumes that maybe predators will avoid eating hyper accumulaters because of the heavy metals. At
this time though scientists have not been able to determine a correlation.[13]
In 2002 a study was done by the Department of Pharmacology at Bangabandhu Sheikh Mujib Medical University in Bangladesh that
used Water Hyacinth to remove arsenic from water.[14] This study proved that water could be completely purified of arsenic in a few hours
and that the plant then could be used as animal feed, fire wood and many other practical purposes. Since water hyacinth is invasive it is
inexpensive to grow and extremely practical.

41. Purification of industrial effluents:
The huge amount of water is used for industrial purposes as a consequence of
rapid industrialization; the problem of industrial effluent has grown significantly.
Since a large majority of industries are water based, a considerable volume of
wastewater emanates from them. Industrial effluents are varied in nature among
industries or even within an industry. Therefore, the problem gets further
aggravated as no standard procedure for treatment can be recommended.
Industrial effluents are generally discharged into surface watercourses, sewers and
on the land, without treatment or inadequately treated. This has created a problem
of surface/subsoil water pollution and soil pollution. Industrial effluents contain
some heavy metals such as Pb, Cd, Zn, Cu and Cr, etc.
Industrial effluents can be treated by natural (sand-gravity-filter), chemical (using
alum, etc.) and by filtering processes. The treated effluents can be discharged into
surface watercourses, sewers and on the land, so the problem of pollution can be
minimized, if not totally eliminated. It is important to bear in mind that some of
the established industrial effluents have a good manorial potential, which should
be exploited. This practice will not only be beneficial for our soil but would also be
a constructive step towards minimizing pollution. Nevertheless, it has to be
ensured that the treated effluent is safe enough to be used for irrigation purposes.

42. C-N sequestration:
State of the different forms of carbon and nitrogen in the soil-plant-water air
environments is known as C-N sequestration. These are influenced by organic
matter composition, recycling susceptibility, the effectiveness of the biological
pump, etc. For example, the long-term effectiveness of the "biological pump"
depends on a net transfer of C from the upper ocean-atmosphere system to the
deep ocean where the C is removed from contact with the atmosphere for an
extended period of time. Approximately 600 GT of dissolved organic carbon
(DOC) are sequestered in the deep sea. The degree of organic matter
biodegradation and recycling depends on the "reactivity" of compounds
synthesized by the biota, which in turn, is controlled by the structural
characteristic of these compounds. There is considerable evidence that different
phytoplankton taxa differ substantially in their biogeochemical characteristics and
it is likely that the relative abundance of different compounds synthesized by these
distinct taxa, and even within each group at different growth conditions, will differ
too. This variability in biosynthesis and thus abundance of a wide range of organic
compounds in the water column would lend itself to different susceptibility for
biodegradation and regeneration.

43. Control of the Soil Biota - Pesticidal control:
Improved crop yields in world agriculture in the past few decades are probably more the
result of pesticidal applications than any other management practice.
What is pesticide?
A pesticide is any agent that controls one or more pest populations. Most modern pesticides
are chemicals broadly classified according to their target population (e.g. herbicides,
control weeds; fungicides, control fungi; insecticides, control insects etc.).
In addition to removing or controlling target pests in the soil/crop system, pesticides in some
way applied to the soil can change the soil ecological balance either by directly affecting
non-target soil organisms or by changing the soil’s physico-chemical characteristics, which
in turn dictates the composition of the soil biota.
Herbicides
Amongst the herbicides, for example, the widely used ‘glyphosate’ is a non-selective, post-
emergence herbicide. It controls almost all annual and perennial weeds through a variety of
possible mechanisms such as reductions in chlorophyll and carotenoid, and increases in
ethylene and cellulase activity (Ashton & Crafts, 1981). It is also systemic, meaning it is a
pesticide that penetrates deep into plant tissue. It is a ‘hormone’ herbicide and its mode of
action is similar to that of natural plant auxins, promoting cell elongation, so that treated
plants show lethally abnormal growth.’Paraquat’. Paraquat is active in the presence of light
and oxygen; the molecule is reduced to radical ions with associated production of hydrogen
peroxide. The peroxide kills the plant through peroxidation of the lipids in the cell
membranes.

44. Fungicides
As with herbicides, fungicides vary greatly in their selectivity and in terms of their
systemic properties. Almost all fungicides, however, must be non-phytotoxic,
‘Captan’ is a non-slective, non-systemic fungicide that reacts with any sulphydryl
compound (Figure 40a). Reaction with any sulphydryl groups (cellular thiols)
produces toxic thiophosgene, which poisons the fungal cell. Many soil fungi may be
affected as a result of foliar spraying of horticultural plants, Captan enters the soil.
Further soil ecological consequences of Captan entering soil are considered for
‘non-target’ population.
Insecticides
A whole host of soil animals that are known to cause crop diseases, particularly
associated with roots, are treated with insecticides. Most of these insecticides are
organophosphorus compounds such as ‘malathion’
Although Malathion is rapidly activated to Malaoxon through oxidative
desulphuration by most soil insects and mammals (Fukuto & Sims, 1971), the soil
and other mammals are able to detoxify Malaoxon to water-soluble excretion
products through carboxyesterase activity. Malathion is therefore active against
soil insects because of their comparatively low carboxyesterase activities. DDT is
an insecticide initially developed for control of the malarial mosquito. Although no
longer used is many countries, its non-target activity has ensured that the soil
ecological ramifications of its use are still being felt.

45. Pesticide type Pesticide Target Soil Population
Insecticides 1. Malathion Aphids, Mites, Thrips, etc.
2. DDT Mosquito Larvae
Fungicides
1. Captan Many Moulds, Scabs, Rots,
Rusts, Blights
2. Carboxin (Oxicarboxin) Cereal rusts, Smuts and Bunts
Herbicides
1. 2,4-D Broad-leaved (dicotyledon)
2. GlyPhosphate Broad-leaved weeds and
grasses (Di-Monocotyledon)
3. Paraquat Broad-leaved weeds and
grasses
Nematocides 1. Nellite Nematods
Mulluscides 1. Methocarb Slugs and Snails
Acaricides 1. Mitac Mites, Scale insects
Some major pesticides and their target soil populations.

46. Pesticidal control of soil processes
Urease activity: Costly losses of nitrogen in agricultural systems that receive
either urea fertilizer or manures are partly caused by excessively high rates of urea
hydrolysis, catalyzed by the soil enzyme urease. The nitrogen loss is largely the result
of volatilization of the ammonia formed by the urea hydrolysis. This gaseous loss can
often account for more than 50% of the applied fertilizer. Losses tend to be highest in
tropical situations where urea/manure is often applied to soil under hot, dry conditions.
Very high rates of ammonia volatilization are not only indicative of fertilizer N-loss, but
may also cause crop damage. The dramatic increase in the use of urea as a nitrogen
fertilizer over recent years, coupled with the known high N-losses associated with urea
application, has focused research on developing pesticides to effectively control the rate
of urea hydrolysis in soil.
Although many compounds have been patented as urease inhibitors over the last few
years, most have proved ineffective and only a few have shown real promise. These
include the phosphoroamides phenylphosphorodiamidate (PDD) as well as N-
butylphosphorothioic triamide (NBPT) & N-(diaminophosphinyl)-cyclohexylamine
(DPCA).
A second approach to minimizing loss of nitrogen from urea fertilizers has
been the use of slow-release fertilizers such as ureaform, which is a reaction product of
urea and formaldehyde. Ureaform consists of a methylene urea polymer of much lower
solubility than urea alone. Sulphur-coated urea is another type of slow-release urea
fertilizer. In both cases, the slower dissolution of the urea enables the crop to compete

47. Nitrification: A range of compounds are now available for the inhibition of nitrification
in soil. The aim of their use is to control the nitrification process in order to couple it
closely with the rate of nitrate uptake by the plant root. This coupling both ensures the
most efficient N-fertilization/nutrition of the plant and minimizes the environmental
pollution that can result from excessive nitrification – nitrate not taken up by the plant
may be subject to leaching into ground and surface waters, as well as to possible
denitrification under anaerobic soil conditions.
The main approach to reducing the potential environmental problems
associated with the use of ammonium-based nitrogen fertilizers and to increase the
recovery of fertilizer nitrogen by crops has been to use compounds that will effectively
inhibit the oxidation of ammonium to nitrite by the microbial nitrifiers in soil. Most
compounds tested have been showed considerable promise as effective inhibitors are (i)
nitrapyrin (‘N-serve’), (ii) dicyandiamide (‘DCD-didin’) and (iii) etridiazole (‘dwell’).
(iv) Acetylene has been found to be an effective inhibitor of ammonium
oxidation in soils and this method of blocking has been used by soil microbiologists
worldwide as a means of characterising soil nitrogen dynamics. Non-gaseous,
substituted acetylene compounds such as phenylacetylene (C6H5C:CH) and
ethynylpyridine (C5H4N)C:CH, therefore, may prove to be successful soil nitrification
inhibitors in the field.
(v) Carbon disulphide has been shown to strongly inhibit nitrification.
Compounds such as xanthates and thiocarbamates, which release carbon disulphide,
may, therefore, be cheap and effective nitrification inhibitors.

48. Combined pesticidal control of urease and nitrification: Ideally, pesticides are needed that are
effective controllers of both urease activity and nitrification in soil although, to date, the most
potent inhibitors of nitrification have proved to be ineffective urease inhibitors and vice versa.
Processes controlling the movement of pesticides in soil
Unfortunately, many pesticides are not deactivated in soil as readily as Paraquat. The
proportion of a pesticide application that leaches to ground water is the result of a number of
processes that occur in the soil, as follows. (a) Transformations including photochemical
processes at the soil surface as well as microbial and chemical transformations in the soil.
Generally, the fraction of a pesticide leached from the soil decreases with increasing rate of
transformation. One therefore expects persistent pesticides to leach more than labile pesticides,
(b) Plant uptake – systemic pesticides will tend to be readily taken up by the plant root. The
extent of this uptake will largely depend on the development of the root system and the
bioavailability of the pesticide, (c) Distribution and transport: pesticides with a high sorption
coefficient (e.g. Paraquat) will tend not to be subject to movement whereas those with a lower
sorption coefficient (e.g. substituted urea herbicides) will be more readily mobilized. Movement
of pesticides through soils occurs both by diffusion and mass flow. Although diffusion can be the
dominant form of herbicide transport in soil, movement via mass flow is generally responsible for
the most widespread distribution of pesticides through soils. Transport of non-sorbet pesticides
and residues by mass flow will largely depend on the hydraulic properties of the soil and the
extent to which rainfall or irrigation exceeds evapotranspiration.
Persistent pesticides with poor sorption properties in soil will tend to be moved through
soil into ground and surface waters most readily, particularly in freely draining soils and
especially after significant events of rainfall/irrigation. More basic research, however, is required
to develop a detailed understanding of the movement of pesticides and residues into
ground/surface waters to ensure the acceptable quality of drinking water supplies.

49. Biological control
It is becoming increasingly recognized that many of the pesticides traditionally used for the control of crop
pests can cause a range of deleterious effects in the environment. Although chemicals are continually being
developed to reduce this environmental risk, an alternative strategy may be required. The use of organisms as
biocontrol agents may provide such a strategy and this area of biotechnology offers considerable promise.
A wide range of biological control agents have been identified, although many more remain to be discovered.
The key target environment for biological control in the soil is the rhizosphere as it represents the zone where
plant infection attack occurs.
Biological control in the rhizosphere
Control of plant pests in the rhizosphere has been associated with a range of soil bacteria and fungi. These
organisms readily appear to utilise Rhizodeposited carbon and successfully colonise the rhizosphere. In the case
of bacteria, the term ‘rhizobacteria’ is used to describe aggressive colonisers of the rhizosphere. Most
rhizobacteria are Gram-negative.
Improved plant growth due to the introduction of rhizobacteria and rhizosphere-colonising fungi may be caused
by a variety of mechanisms, including biological control of pests. In the case of bacteria, the term ‘plant-
growth-promoting rhizobacteria’ or ‘PGPR’ is used when any beneficial effects on plant growth result from
bacterial activity in the rhizosphere.
Bio-fertilization by Mycorrhizal Fungal Inoculation/Potential benefits of mycorrhizal fungal inoculation
The potential benefits of mycorrhizal fungal inoculation for bio-fertilizing arable and forest crops are very
considerable. These benefits to the plant host range from enhanced nutrient uptake, through increased tolerance
of the host to environmental stresses such as soil water stress and heavy-metal toxicity, to enhanced resistance
to many of the soil-borne pathogenic microbes.
Mycorrhizally infected plants can also be linked via their mycorrhizal fungal hyphae and these links can
provide the means of inter-plant transfer of photosynthate and other nutrients. Inter-plant transfer for both
ectomycorrhizal and VAM systems has been demonstrated and the suggestion made that these mycorrhizal
pathways facilitate nutrient conservation at the ecosystem level. In arable situations, however, mycorrhizal
fungal transfer of nitrogen from legumes to non-legumes is unlikely to offer a realistic alternative to
conventional fertilizing. This is because the transfer is unlikely.

50. Biogenic trace gases
Once life formed, it was protected from biologically lethal solar ultraviolet radiation by
the presence of atmospheric O3, which is produced via photochemical processes from
O2, a biogenic gas (Levine 1985). The biogenic gases produced metabolically by
various microorganisms are –
1) N2, 2) O2, 3) CO2, 4) N2O, 5) NH3, 6) CH4, 7) CO, 8) H2, 9) H2S, 10) Dimethyl
sulfide [(CH3)2S]. To this list some other biogenic gases as stated below may be
added:
11) Nitric oxide (NO), 12) Dimethyl disulfide [(CH3)2S2], 13) Methyl halogens [i.e.
methyl chloride (CH3Cl), methyl bromide (CH3Br), and methyl iodide (CH3I)].
For some of these gases, biogenic production is the overwhelming source [e.g. O2,
N2O, NH3, CH4, H2S, (CH3)2S and (CH3)2S2]. For others, the strength of the biogenic
source is not accurately known but is probably significant [e.g. CO, NO, H2 and methyl
halogens]
All these biogenic species, even at trace levels, impact the photochemistry and
chemistry of the lower and upper atmosphere, lead to the formation of acid
precipitation and atmospheric aerosols and affect the climate of the Earth via
greenhouse effect.

51. Photochemistry of oxygen, ozone and OH radical:
The most important biogenic species in the atmosphere is
molecular oxygen (O2) produced as a by-product during the
process of photosynthesis, which can be expressed by the
following reaction:
Chlorophyll
nH2O + mCO2 + hv  Cm(H2O)n + mO2 (1)
In equation (1), Cm(H2O)n represents carbohydrate
produced by the green plant cell from water vapor (H2O)
and carbon dioxide (CO2) in the presence of sunlight,
represented by hv, where h is Planck’s constant and v is the
frequency of the visible solar radiation. The carbohydrate
produced in the photosynthetic process is utilized as food
by the plant.

52. The photochemical reactions leading to the abiotic production of O2 can be expressed
as:
H2O + hv  OH + H; 240 nm (2)
followed by : OH + OH  O + H2O (3) And
CO2 + hv  O + CO; 230 nm (4)
The atomic oxygen (O) produced in reactions (3) and (4) forms O2 via the following
reactions: O + O + M  O2 + M, (5) And
O + OH  O2 + H (6)
Where OH is the hydroxyl radical, CO is carbon monoxide, H is atomic hydrogen, and
M is any molecule to absorb excess energy and/or momentum of the reaction. The
abiotic production of O2 via reactions (2) to (6) is very sensitive to atmospheric levels
of H20 and C02, and to the flux of solar ultraviolet radiation, all of which may have
varied significantly over geological time (Canuto et al., 1982). The biogenic growth of
O2 in the atmosphere had another important biological effect – it led to the
photochemical production of ozone (O3), which eventually resulted in the shielding of
the Earth’s surface from biologically lethal solar ultraviolet radiation. The
photochemical production of O3 is initiated by the photolysis of O2-forming oxygen
atoms (O), which then may recombine to form O3. These reactions can be expressed
as:
O2 + hv  O + O; 242 nm (7)

53. Followed by:
O + O2 + M  O3 + M (8)
The calculated vertical distribution of O3 as a function of atmospheric O2 level,
expressed in present atmospheric level (PAL) of O2.
In the present atmosphere, O3 not only shields the surface of the Earth from
biologically lethal solar ultraviolet radiation, but also initiates a photochemical
reaction that leads to the chemical transformation of almost every biogenically
produced gas. Biogenic gases are transformed via oxidation by the hydroxyl radical
(OH). The hydroxyl radical is produced by the reaction of excited oxygen [O(‘D)] with
water vapor. Excited oxygen results from the photolysis of O3. These processes can be
represented by the following reactions:
O3 + hv O(‘D)  O2 + O(‘D); 310 nm (9)
O(‘D) + H2O  OH (10)
The transfer of solar radiation through the atmosphere that leads to the production of
[O(‘D)] via the photolysis of O3 (reaction, 9) is controlled by molecular absorption,
multiple scattering due to atmospheric molecules and aerosol particles, and surface
albedo.
Surface albedo 0 percent means total absorption by the surface;
Surface albedo 100 percent means total reflection by the surface;
The global albedo of the Earth is about 25 to 30%.

54. The chemical destruction of NH3 is controlled by its reaction with OH:
NH3 + OH  NH2 + H2O (11)
This reaction leads to the formation of the amine radical (NH2).
Subsequent reactions of the amine radical may lead to either the
production or destruction of the oxides of nitrogen (NOx + NO2) via the
following reactions (Logan et al., 1981):
NH2 + O3  NOx + products (12)
NH2 + NO  N2 + H2O (13)
NH2 + NO2  N2O + H2O (14)
For NOx concentrations below about 60 pptv the reactions (12) to (14)
lead to a net production of NOx, whereas for NOx concentrations greater
than 60 pptv, these reactions lead to a net destruction of NOx (Logan et
al., 1981).
The atmospheric loss of NH3 is controlled by rainout with a
characteristic loss time of about ten days (Levine et al., 1980). Another
heterogeneous process that leads to the atmospheric loss of NH3 is the
formation of ammonium nitrate (NH4NO3) and ammonium sulfate
[(NH4)2SO4] aerosols via the following reactions :

55. NH3(g) + HNO3(g)  NH4NO3(s) (15) And
2NH3(g) + H2SO4(g)  (NH4)2SO4(s) (16)
(g denotes gaseous phase; s denotes solid phase).
The loss of atmospheric NH3 via rainout, aerosol formation, and dry
deposition is a source of ammonium ions (NH4
+) to the biosphere.
It should be pointed out that O3 may also be photolyzed by solar
radiation of wavelength greater than 310 nm, but this reaction leads to
the production of ground state atomic oxygen (O) rather than the more
energetic excited oxygen [O(‘D)]. Solar photons between about 290 nm-
310 nm can reach the Earth’s surface (stratospheric O3 absorbs solar
photons less than about 290 nm and, hence, they cannot reach the
troposphere). However, in the O2 and O3 deficient paleoatmosphere,
solar photons less than 290 nm could easily reach the surface and the
direct photolysis of H2O like reaction (2) was a major source of OH in the
pre-biological paleoatmosphere.

56. Photochemistry of methane (CH4)
After carbon dioxide (CO2: mixing ratio is about 330 ppmv), methane, is the most abundant carbon species.
Duetoitsrelativelylongatmosphericresidencetime(abouteight years),CH4 appearstobeuniformlymixed
with respect to altitude within the troposphere, but exhibits a slight latitudinal gradient. Tropospheric levels
ofmethanehaveincreasedsignificantly,withthecurrentannualincreaseabout1to2 %per year.
Methaneabsorbsthermal infraredradiationatabout7.7µm(Wangetal.,1976).AnincreaseinCH4 from0.7
ppmv to its present value of about 1.66 ppmv may have caused an increase in the global temperature of the
Earth of about 0.23ºC (Wanget al., 1976), which is about half of the temperature increase calculated to have
occurred as a result of increases in atmospheric CO2. Methane is produced byfermentation of organic matter
inanoxicenvironments,suchasswamps,tropicalrainforests,andricepaddies(HarrissandSebacher,1981).
Other sources of CH4 include enteric fermentation in ruminants (mostlycattle), biomass burning, natural gas
leakage (Ehhalt and Schmidt, 1978), and termites (Zimmerman et al., 1982). Reaction with OH is the
overwhelmingloss mechanism forCH4 viathefollowingreaction:
CH4 + OH  CH3 + H2O (17)

57. This reaction leads to the formation of the methyl radical (CH3). Subsequent reactions of the methyl radical,
initiated by reaction (17), form the methane oxidation scheme, which is summarized below (Logan et al.,
1981):
CH3 + O2 + M  CH3O2 + M (18)
(CH3O2 = methylperoxyl radical)
CH3O2 + NO  CH3O + NO2 (19)
(CH3O = methoxyl radical)
NO2 + hv  NO + O; 400 nm (20)
O + O2 + M  O3 + M (8)
CH3 + O2  H2CO + HO2 (21)
(H2CO = formaldehyde; HO2 = hydroperoxyl radical)
HO2 + NO  NO2 + OH (22)
NO2 + hv  NO + O; 400 nm (20)
O + O2 + M  O3 + M (8)
H2CO + hv  CO + H2, or HCO + H; 340 nm (23)
The net cycle for the methane oxidation scheme can be represented as:
CH4 + 4 O2  H2O + CO + H2 + 2 O3 (net cycle) (24)

58. Reduced sulfur species
Hydrogen sulfide (H2S), dimethyl sulfide [(CH3)2S], and dimethyl disulfide [(CH3)2S2] are biogenically
produced sulfur species. Bacteria in anaerobic, sulfate-rich environments, such as marine sediments and
coastal mud flats, produce these gases. Reaction with OH is the major chemical loss for these gases. The
oxidation of H2S by OH leads to the production of sulfur dioxide (SO2) and eventually sulfuric acid (H2SO4),
the major constituent of acid rain. The reaction scheme of (CH3)2S and (CH3)2S2 with OH is less certain, but
is also believed to lead to the formation of SO2 and H2SO4. The reactions describing the oxidation of H2S to
H2SO4 are summarized below (Graedel, 1979):
H2S + OH  HS + H2O (25)
(HS = thiohydroxyl radical)
HS + O2  SO + OH (26)
(SO = sulfoxyl radical)
SO + O2  SO2 + O (27)
SO2 + OH + M  HSO3 + M (28)
(HSO3 = sulfuric acid radical)
HSO3 + OH  H2SO4 (29)
Several other reaction schemes have been suggested for the transformation of SO2 to H2SO4. These include:
SO2 + HO2  SO3 + OH (30)
(SO3 = sulfur trioxide)
SO3 + H2O  H2SO4 (31)

59. Photochemistry of reduced halogen species
It has been suggested that methyl chloride (CH3CL: 0.5 ppbv), methyl
bromide (CH3Br: 10 pptv), and methyl iodide (CH3I: 1 pptv) are
produced biogenically in the ocean as well as by anthropogenic
activities. A mechanism for the oxidation of CH3Cl by OH is described
as follows (Graedel, 1979):
CH3Cl + OH  CH2Cl + H2O (32)
(CH2Cl = chloromethyl radical)
CH2Cl + O2 + M  CH2ClO2 + M (33)
CH2ClO2 + NO  CH2ClO + NO2 (34)
CH2ClO + O2  HCl + CO + HO2 (35)
(HCl = hydrogen chloride)
Similar reactions are probably initiated by the oxidation of CH3Br and
CH3I by OH.

60. Photochemistry of carbon monoxide (CO)
The mixing ratio of carbon monoxide (CO), which exhibits a strong latitudinal gradient
(70 to 200 ppbv in the Northern Hemisphere and 40 to 60 ppbv in the Southern
Hemisphere), suggests a strong, if not dominant, anthropogenic source (Logan et al.,
1981). The magnitude of the biogenic source of CO remains uncertain. Atmospheric
CO has an atmospheric residence time of about three months and is controlled by its
reaction time with OH, which initiates the carbon monoxide oxidation scheme,
summarized below (Logan et al., 1981):
CO + OH  CO2 + H (36)
H + O2 + M  HO2 + M (37)
HO2 + NO  NO2 + OH (38)
NO2 + hv  NO + O; 400 nm (20)
O + O2 + M  O3 + M (8)
Assuming sufficient levels of NO for reaction (38) to proceed, the net cycle for the
carbon monoxide oxidation scheme can be represented as:
CO + 2 O2  CO2 + O3 (net cycle) (39)
Continuous in situ measurements (Khalil and Rasmussen, 1984) and analysis of
historic ground based solar infared spectra (Rinsland and Levine, 1985) indicate that
atmospheric levels of CO may be increasing between about 1 to 5 percent per year.
This CO increase combined with increasing levels of CH4 suggests that tropospheric
levels of OH may have decreased by about 25 percent over the last 35 years (Levine et
al., 1985).

61. Photochemistry of nitric oxide (NO)
Nitric oxide (NO) is biogenically produced by several bacteria (Lipschultz et al., 1981;
Anderson and Levine, 1986, 1987). The magnitude of the biogenic source is uncertain
and may be comparable to (Galbally and Roy, 1978) or significantly less than the
anthropogenic source of NO (i.e., high temperature combustion processes are believed
to be the major source of NO: Crutzen, 1979). Nitric oxide is rapidly converted to
nitrogen dioxide (NO2) by reacting with O3 and HO2:
NO + O3  NO2 + O2 (40)
NO + HO2  NO2 + OH (41)
The photolysis of NO2 leads to the rapid formation of NO:
NO2 + hv  NO + O; 400 nm (20)
The reaction of NO with OH leads to the formation of nitrous acid (HNO2):
NO + OH + M  HNO2 + M (42)
The NO2 produced in reactions (40) and (41) reacts with OH to form nitric acid
(HNO3), the fastest increasing component of acid rain:
NO2 + OH + M  HNO3 + M (43)
The loss of water-soluble HNO3, which has a characteristic atmospheric residence time of about
three days, is controlled by rainout. The loss of HNO3 and HNO2 by rainout and other
heterogeneous loss mechanisms (e.g., dry deposition and aerosol formation) are the major loss
mechanisms for the oxides of nitrogen (NOx = NO + NO2) in the atmosphere. Nitric and nitrous
acids are sources of fixed nitrogen (i.e., nitrates (NO3
-) and nitrites (NO2
-) to the biosphere. Once
in the biosphere, NO3
-, NO2
-, and NH4
+ are recycled into the atmosphere in the forms of
molecular nitrogen (N2), nitrous oxide (N2O), and NO via nitrification and denitrification.

62. Photochemistry of nitrous oxide (N2O)
Main source of N2O is biogenic. Soil bacteria via nitrification and/or denitrification may
biogenically produce N2O, depending on the soil conditions. Nitrous oxide is chemically inert in
the troposphere and has a characteristic atmospheric residence time of about 150 years. Nitrous
oxide is destroyed in the stratosphere by photolysis and by reactions with excited atomic oxygen
[O('D)], according to the following reactions:
N2O + hv  N2 + O('D); 337 nm (44)
N2O + O('D)  N2 + O2 (45)
N2O + O('D)  2 NO (46)
Reaction (44) is the major loss mechanism for N2O and, with reaction (46), the major source of
NO in the stratosphere. The catalytic nitrogen oxide cycle that leads to the destruction of O3 in
the stratosphere can be expressed as:
NO + O3  NO2 + O2 (40)
NO2 + O  NO + O2 (47)
NO is also formed by the photolysis of NO2:
NO2 + hv  NO + O (20)
Reactions (40) and (47) result in a net cycle of:
O3 + O  2 O2 (net cycle) (48)
Nitrous oxide absorbs in the thermal infrared at 7.5 µm and, hence, affects the climate of the Earth.
Since all the destruction of N2O occurs in the stratosphere via reactions (44) to (46), N2O exhibits
a constant mixing ratio with altitude within the global troposphere. Recent measurements indicate
that global concentrations of N2O may be increasing with time, at a rate of about 0.2 percent per
year. While biogenic production appears to be the major source of N2O, the combustion of fossil
fuel and/or agricultural activity may be responsible for the apparent secular increase of this
species.

63. Photochemistry of nitrogen (N2) and carbon dioxide (CO2)
While the bulk of atmospheric nitrogen (78% by volume) and carbon dioxide (about
340 ppmv) probably resulted from volcanic activity in the early history of our planet
(the average composition of volcanic gases is H2O (79.31%), CO2 (11.61%), SO2
(6.48%), and N2 (1.29%; Walker, 1977), both these gases are also formed biogenically.
Nitrogen is formed via denitrification and carbon dioxide is formed as a respiration and
metabolic product. Both N2 and CO2 are chemically inert in the atmosphere. However,
very small amounts of N2 are fixed into NO by the action of atmospheric lightning
(Levine et al., 1981, 1984). As already discussed, NO is photochemically transformed
to HNO3 and HNO2, and is eventually returned to the biosphere in the form of nitrates
and nitrites, respectively. There does not appear to be any significant atmospheric sink.
The oceans are probably the major sinks for this nitrogen gas (Woodwell et al., 1978;
Broecker et al., 1979). Atmospheric CO2 has increased from about 280 ppmv to 300
ppmv around 1880 to about 335 ppmv to 340 ppmv in 1980 (Siegenthaler and
Oeschger, 1978), mainly due to the burning of fossil fuels (at a given location CO2
exhibits a strong seasonal variation of several ppmv due to its uptake via photosynthesis
in spring and summer). Carbon dioxide absorbs thermal infrared radiation in the
atmospheric window (7 µm to 14 µm). Various theoretical radiative-temperature
calculations indicate a global temperature increase of between 2 to 3.5º C for a doubling
of the present level of atmospheric CO2, with a strong amplification (8 to 10ºC
warming) in the polar areas (Siegenthaler and Oeschger, 1978).

64. Atmospheric concentrations of the major greenhouse gases, their rise,
residence time and contribution to the global warming.
Type Residence
time
(year)
Annual
rise (%)
Atmospheric
Concentration
(1985)
Contribution
to global
warming (%)
Radiative absorption
potential (time)
CO2 100 0.5 345 ppmv 50 1
CO 0.2 0.6 -1.0 90 ppbv (n.a) (n.a)
CH4 8 -12 1 1.65 ppmv 19 32
N2O 100 - 200 0.25 300 ppbv 4 150
O3 0.1- 0.3 2.0 (n.a) 8 2,000
CFCs 65 – 110
(60 – 120)
3.0 0.18 - 0.28
ppbv
15 > 10,000
CFC-11 and other derivatives; CHCl2F2(CFC-12), CHCl2F2(HCFC-22);
CHCl2CF3(HCFC-123).

65. Formation of ozone
If it wasn't for stratospheric ozone, life wouldn't be possible on Earth. Ozone
prevents harmful ultra-violet radiation from the Sun (light with wavelengths less
than 320 nm) reaching the ground. If allowed to reach Earth, this radiation would
severely damage the cells that plants and animals are made up of. Ozone was first
formed in the Earth's atmosphere after the release of oxygen, between 2000 and
600 million years before the first humans appeared.
Ozone formation and destruction
Two forms of oxygen are found in the stratosphere. Molecular oxygen (O2), which
is made up of two atoms of oxygen (O), and ozone (O3), which, as you can see from
its chemical formula, is, made up of three oxygen atoms. Ozone is formed when
intensive ultra-violet radiation from the Sun breaks down O2 into two oxygen
atoms. These highly reactive oxygen atoms can then react with more O2 to form
O3. In a similar way, ozone is destroyed by solar radiation. Ultraviolet radiation
hits ozone and breaks it back down into molecular oxygen (O2) and atomic oxygen
(O). The oxygen atom O then reacts with another ozone molecule to form two
oxygen molecules.

66. Thickness of the ozone layer
The term "ozone layer" is often misunderstood. It’s not really a single layer in the
atmosphere (atm.) where ozone is concentrated. Rather it means that a higher fraction
of ozone molecules are found in the stratosphere (at altitudes between 18 and 40 km)
compared to levels the troposphere below or the mesosphere above. In reality, only
about 10 out of every million molecules in the atm. are actually ozone but 90% of all the
ozone present in the atm. is found in the stratosphere.
An ozone hole was first observed in 1956!
G.M.B. Dobson (Exploring the Atm., 2nd Edn., Oxford, 1968) mentioned that when
springtime ozone levels over Halley Bay were first measured, he was surprised to find
that they were ~320 DU, about 150 DU below spring levels, ~450 DU, in the Arctic.
These, however, were the pre-ozone hole normal climatological values. What Dobson
describes is essentially the baseline from which the ozone hole is measured: actual
ozone hole values are in the 150-100 DU range.
Dobson units (DU)
You will often see ozone levels reported in Dobson (as per the name of G.M.B. Dobson)
units (DU). The 300 DU is a typical value. But what does this mean? If we assume that all
the ozone molecules in the atmosphere were concentrated in a small layer at the
ground (rather than being spread over the whole stratosphere and troposphere) then
thickness of this layer would be about 3 mm. Since 1 DU is equivalent to a layer of pure
ozone molecules 0.01 mm thick, a 3 mm layer of ozone is equivalent to a value of 300
DU.

67. Ozone destruction or depletion
Ozone depletion refers to the phenomenon of reductions in the amount of ozone in the stratosphere. There
was a reduction of approximately 5% detected from 1979 to 1990. Since the ozone layer prevents most
harmful wavelengths of ultraviolet light from passing through the Earth's atmosphere, observed and
projected decreases in ozone have generated worldwide concern and led to adoption of the Montreal
Protocol banning the use of chlorofluorocarbon (CFC) compounds, as well as other ozone depleting
chemicals such as carbon tetrachloride, trichloroethane (also known as methyl chloroform), and bromine
compounds known as halons. Ozone depletion varies geographically and by season. The term ozone hole
refers to the annual, temporary reductions in the polar regions, where large losses in ozone occur each
spring (up to 70% over 25 million km2 of Antarctica and 30% over the Arctic) followed by recovery in
the summer. Increases in concentrations of stratospheric chlorine from breakdown of human
manufactured CFC emissions, as well as other gases cause this reduction.
Chemical factors
Ozone can be destroyed by a number of free radical catalysts, of which the most important are hydroxyl
(OH), nitric oxide (NO) and atomic chlorine (Cl) and bromine (Br). All of these radicals have both natural
and anthropogenic (manmade) sources. At the present time, most of the OH and NO in the stratosphere is
of natural origin, but human activity has dramatically increased the chlorine and bromine. These elements
are found in certain stable compounds, especially chlorofluorocarbons (CFCs), which may find their way
to the stratosphere and there be liberated by the action of ultraviolet light. Most importantly, the chlorine
atoms so generated destroy ozone molecules in a catalytic cycle. In this cycle, a chlorine atom reacts with
an ozone molecule, taking an oxygen atom with it (forming ClO) and leaving a normal oxygen molecule.
A free oxygen atom then takes away the oxygen from the ClO, and the final result is an oxygen molecule
and a chlorine atom, which then reinitiates the cycle. A single chlorine atom would keep on destroying
ozone forever were it not for reactions that remove them from this cycle by forming reservoir species
such as hydrochloric acid and chlorine nitrate. On a per atom basis, bromine is even more efficient than
chlorine at destroying ozone, but there is much less bromine in the atmosphere at present. As a result,
both chlorine and bromine contribute significantly to the overall ozone depletion.

68. Polar stratospheric clouds
The reactivation of atomic chlorine from these reservoir species is
normally slow, but is enhanced by the presence of polar stratospheric
clouds, which appear during Antarctic winters, leading to a strong
seasonal cycle in ozone hole formation.
Consequences of ozone depletion
Since the ozone layer absorbs ultraviolet light from the Sun, ozone layer
depletion is expected to increase surface UV levels, which could lead to
damage, including increases in skin cancer. This was the reason for the
Montreal Protocol. Although decreases in stratospheric ozone are well-
tied to CFCs, and there are good theoretical reasons to believe that
decreases in ozone will lead to increases in surface UV, there is not much
direct observational evidence linking ozone depletion to higher incidence
of skin cancer in human beings.

69. AGRICULTURAL CONTRIBUTION TO GLOBAL CLIMATE CHANGE
Average global surface temperatures have varied by 5 to 7ºC over 100,000-yrs.
and by 2ºC in the 10,000 yrs. since the last ice age.
Average global surface temperatures have, in fact, increased by 0.45 ± 0.15ºC in the last
century.
Simulation of climate through atmospheric general circulation models (GCM’s) is the
principal methodology by which anthropogenic effects on climate are evaluated and
projected. Much attention has been given to prediction of the climate effects of
doubling the atmospheric CO2 level since this could occur by the middle of the next
century. For this situation, the various GCM’s predicted an average global warming
between 1.5 and 4.5ºC, and changes in global rainfall amounts and distribution.
Furthermore, the combined effect of increases in other trace gases, viz. CH4, N20,
chlorofluorocarbons (CFCs), and ozone (O3) presently contribute about as much to
greenhouse forcing in the atmosphere, as does CO2.
The radiative balance of the atmosphere controls the Earth’s climate. The Earth absorbs
about one-half of the short wave radiation it intercepts and emits longer wave thermal
infrared radiation from its surface. On a long-term basis the energy of incoming
radiation is balanced by that of outgoing radiation. The greenhouse effect occurs
because some of the atmospheric trace gases, notably water vapor and CO2, partially
absorb infrared radiation coming from the Earth’s surface, leading to a warming of the
atmosphere.

70. Table. Effects of greenhouse gases on different planets.
Surface
pressure
relative to
earth
Main
greenhouse
gases
Surface temp.
without green-
house effect (ºC)
Observed
surface
temp. (ºC)
Greenhouse
warming
(ºC)
Venus
Earth
Mars
90
1
0.007
>90% CO2
0.035% CO2
1% H2O
>80% CO2
-46
-18
-57
477
15
-47
523
33
10

71. Changes in greenhouse gas levels
Atmospheric concentrations of CO2, CH4, and N2O increased slowly
between 1750 and 1950, then increased rather abruptly between 1950
and present.
The recent global distribution of atmospheric CO2 revealed –
(i) a general increase in concentration with time,
(ii) higher levels in the northern hemisphere associated with greater
land mass and source strength in this hemisphere, and
(iii) seasonal fluctuations that are caused by climate-controlled cycles
of production and consumption.

72. Global warming potentials and radiative forcing of climate
A single index, called the Global Warming Potential (GWP), has been developed to compare the
relative greenhouse effects of different trace gases.
The GWP concept combines the capacity of a gas to absorb infrared radiation, its residence time
in the atmosphere, and a time frame over which climate effects are to be evaluated.
The atmospheric life times of the gases will remain constant over time, are probably incorrect.
Although the process of calculating GWP’s is complex and imperfect at present, the results serve
to illustrate important differences between the trace gases.
Methane, which has a much shorter atmospheric residence time (10 yr.) than CO2 (120 yr), has a
60-fold higher GWP in a 20-yrs. time frame due partly to its greater absorptive capacity (direct
effect) and partly to the generation of CO2, tropospheric O3, and stratospheric water vapor from
its atmospheric chemistry (indirect effects). Over a 500 yrs. time frame, CH4 still has a 9-fold
larger GWP than CO2, which is mostly due to indirect effects rather than to CH4 directly.
Nitrous oxide has an atmospheric residence time similar to CO2 but a 200 fold greater absorptive
capacity and a correspondingly higher GWP than CO2. It is also a more effective greenhouse gas
than CH4, especially on the longer-term basis.
The CFC’s and HCFC’s have absorption capacities from one to over three orders of magnitude
greater than the other trace gases, but generally similar residence times so all are extremely
potent greenhouse gases. Of several possible CFC substitutes, HCFC-123 (CHCl2CF3) has the
lowest GWP, primarily because of its relatively short atmospheric residence time of 1.6 yrs.
Increases in atmospheric CO2 levels have been, and continue to be, the main contributor to
radiative forcing, accounting for 61% of the overall change and 56% in the last decade.
Since 1960, the CFC’s and N2O have made progressively larger contributions, whereas the effect
of CH has remained more or less constant.

73. Agricultural contributions to trace gas emissions and global warming
Fossil fuel use and activities associated with its extraction and transport are major
contributors, but agricultural activities account for about one-quarter of the total effect.
Two-thirds of the agricultural contribution is related to agricultural practices and one-
third is associated with conversion of land to agricultural use, principally deforestation
in the tropics.
Estimated annual budgets for CO2, N2O, and CH4 and the contributions of agriculture to
these budgets are presented in the enclosed Table *. Anthropogenic activities are much
more important sources of CH4 and N2O than that of CO2, accounting for 64, 24, and
3%, respectively of total emissions of these gases. The net annual flux, determined by
subtracting total sink strength from total source strength, does not balance the observed
rate of increase in atmospheric content for any of the gases, it must be recognized that
there is considerable uncertainty in many of the source-sink estimates. For CO2, the
anthropogenically-derived component is only 3% of total sources but emissions of CO2
from fossil fuel combustion, the major anthropogenic source, are well documented.
Therefore, it is clear that either the agricultural contribution associated with
deforestation and loss of soil organic matter has been overestimated or that a sink has
been underestimated or not identified.

75. The anthropogenic activities related to agriculture have contributed significantly to rising
atmospheric CO2 levels in the last 150 yrs., the major anthropogenic flux today comes from fossil
fuel combustion, which added 5.7 Gt CO2-C to the atmosphere in 1987. Current release of CO2
due to conversion of land to agriculture is estimated to be between 0.6 to 2.6 Gt C yr-1 with a
value of 1.6 Gt C yr-1 often being used. In contrast, several dynamic simulation models suggest
that current losses of C due to land conversion to agriculture are balanced by increased net
primary productivity (NPP) in native terrestrial ecosystems, which leads to greater C storage in
both aboveground biomass and soil organic matter. Increased NPP is postulated to be due to
higher atmospheric CO2 levels, i.e., to a CO2 fertilization effect. Fertilization effects are, however,
difficult to evaluate because the terrestrial biomass and soil organic matter pool sizes are 250 to
750 times larger than the imbalance in the annual C budget.
Anthropogenic sources account for 64% of total CH4 emissions. Agriculture and related activities
contribute two-thirds of the anthropogenic source or 41% of all sources. This production is offset
by oxidation of CH4, which largely takes place in the atmosphere through reaction with the OH
radical. Since CH4 source budgets are often “balanced” against destruction, the recent discovery
showed that the rate coefficient for the reaction of .OH with CH4 is about one-fourth less than
previously thought brings considerable uncertainty to the global atmospheric CH4 budget.
Additionally, the recent observation evinced that CH4 is consumed in soils introduces a new term
for consideration in the global CH4 budget as soil CH4 sink. Current global terrestrial CH4 sink is
estimated as about 20 to 33 Tg CH4-C yr-1 or between 5 to 8% of total sources. Because the
annual production of tropospheric OH is almost all consumed by reaction with CH4 and CO. It is
possible that further increases in CH4 emissions will saturate the atmospheric capacity for its
oxidation, leading to greater persistence of CH4. Increases in the concentration of atmospheric
CH4 will increase the importance of the soil CH4 sink.

76. The annual budget for N2O appears to underestimate sources, although high spatial and temporal
variability make these particularly difficult to estimate. Tropical forests are estimated to
contribute 40% of natural sources, but the database is somewhat limited. More rapid N cycling in
the tropical environment is considered to cause higher N2O emissions that found in cooler
climates. Anthropogenic activities appear to have increased N2O emissions by about one-third of
the baseline value, and increased emissions are almost totally associated with agriculture.
Nitrous oxide production resulting from fertilizer and increased use of BNF is underestimated
because the effect of N input is usually only partially traced through the environment. If N2O
comprises 10% of the volatilized N, 2 kg N2O-N would be generated in the primary cycle. If
assessment of the fertilizer effect stops at this point, and most do, only 20 of the 100 kg N has
been returned to the atmosphere, yet a reasonable assumption is that almost all of it would be
returned within a time frame of a few years. The manure is returned to cropland to create a
secondary crop cycle, however, about one-half of the N in manure is volatilized as NH3 prior to
or during manure application. Volatilized NH3 is aerially dispersed and subsequently returned to
and cycled through both natural ecosystems and cropland. Ammonia volatilization from
agricultural systems is globally important but its impact on N2O emissions has not been explicitly
addressed. In U.S. agric., the annual production of animal manure N is equal to the annual use of
fert. N and probably 30 of the 80 Tg fertilizers N per year used globally are volatilized as NH3.
Similarly, the amount of N2O arising from leached NO3
-, which may average 20 to 25% of
applied N, is not known but much may be denitrified in riparian zones or cycled through wetland
or aquatic vegetation. A complete accounting of fertilizer and biologically fixed N is difficult to
achieve but needed, if we are to accurately assess the impact of increased use of N in agricultural
ecosystems on terrestrial N2O emissions.