Unit I
UNDERSTANDING ENVIRONMENT
1.1 The Environment
The word environment is derived from a French word ‘Environner’, which means to encircle or
surround. Environment can be defined as the sum total of external factors, substances and
conditions which influence organisms. Environment is usually divided into two parts.
• The physical environment consists of forces of nature like wind, gravity, conditions like
temperature and light, time, and non-living materials like soil and water.
• The biotic environment is made of all living beings including their reactions, interactions
and interrelated actions. Any constituent or condition of the environment which affects
directly or indirectly the form of functioning of the organism in any specific way is called
environmental factor or ecological factor.
It is universally accepted that environment creates favorable conditions for the existence and
development of living organisms. The environment for any living organism has never been
constant or static. It has always been changing sometimes slowly and sometimes rapidly or
drastically. Like other organisms, man is also affected by his environment and these changes in
environment may benefit or harm him. Thus, we can say that every living species of plants or
animals influence its environment and in turn gets influenced by it.
Since the ancient times, man started interfering with the environment; he devastated forests by
cutting down trees for the wood and for other household needs. He removed stretches of forests
for bringing land under cultivation. He killed the animals; the gentle ones for blood and the
fierier ones for safety. He has polluted rivers with chemicals from factories, thereby making the
water unfit for his needs. All these activities however did not affect the environment too
seriously up to a fairly long time because population was not too high and life style was not so
complex.
No country in the world can build a brick wall around its air, so if the air pollution occurs in one
part, it is likely to affect another part of world. And who is to blame for all this; certainly the one
and the only man who has actively damaged and polluted the environment, thereby interfering
with natural processes and trying to twist them to his advantage.
In short we can say that the way we are exploiting, deteriorating and polluting the environment
will take ages to discuss and write.
Let take pledge today to safe guard Mother –Earth.
Environmental Science and Its Multidisciplinary Nature
Environmental science in its broader sense is “the science of complex interactions that occur
among the terrestrial, aerial, aquatic and living environments”. It includes all the disciplines such
as chemistry, physics, biology, microbiology, toxicology, law, sociology, ecology etc. that affect
or describe these interactions. In simple sense environmental science can be defined as the study
of the earth, air, water and the living environment and the effects of technology on it.
The current interest in the states of environment began with the philosophers like Thoreau but
received an additional attention by the organization of the first earth day on 22ndApril 1970 and
Stockholm Conference on 5th June 1972. This commitment was further enhanced by Rio
Conference on 13th June 1992. As a result, environmental science is now a standard course. Most
of the concepts covered by environmental science courses have been previously taught in
ecology, conservation, geography etc. The physical and biological ideas were incorporated,
along with input from social sciences such as economics, sociology and political science, into a
new multidisciplinary field of environmental science.
Scope and Importance of Environmental Science
Environmental science is an interdisciplinary and multidisciplinary subject in its scope. It
enables us to understand the following main components of environmental management.
• Environment perception and people awareness.
• Control of environmental degradation and pollution.
• Control of over population and over consumption.
• Maintenance of environmental quality.
• To restrict and regulate the exploitation of natural resources.
• Environmental science helps us to adopt engineered technology without creating adverse
effects on the environment.
• Helps us to participate in afforestation programmes.
• Helps us to participate in programmes aimed at minimising air, water and noise pollution.
Although all the above points of environment management are of extreme importance, yet it is
quoted.
“If you plan for one year, plant rice.
If you plan for ten, years grow trees.
If you plan for hundred years, educate the people”.
Importance of Environmental Science
Environmental science has become a very important subject as it addresses many issues like;
• Global warming and climate change
• Ozone layer depletion
• Acid rain
• Pollution
• Over population
• Sustainable development
• Over exploitation of natural resources
Environment which is global in nature belongs to all and is thus important for all. Every person
irrespective of age or gender will be affected by environment and will also affect the
environment by their deeds. Example atmosphere has no boundaries and thus pollutants
produced at one place can be dispersed and transported to other place. The river water polluted at
one point can ultimately affect the whole aquatic life.
1.2 Components of environment
As mentioned previously Environment can be broadly defined as one’s surroundings. To be more
specific we can say that it is the physical and biological habitat that surrounds us. The
environment can be divided into two broad components as follows:
(A) Abiotic Component: External physical factors like air, water, and land etc. This is also
called the Physical Environment.
(B) Biotic Component: All living organisms around us viz. plants, animals, and
microorganisms. This is also called the Living Environment.
Earth’s environment can be further subdivided into the following four segments:
A. Lithosphere
B. Hydrosphere
C. Atmosphere
D. Biosphere
A. Atmosphere
The Atmosphere is an abiotic component of our environment. It is a complex fluid of gases,
water vapours and suspended particles that form an envelope around the Earth. The Atmosphere
can be vertically divided into various layers based on temperature and composition of gases.
These layers are;
a) Troposphere
b) Stratosphere
c) Mesosphere
d) Thermosphere
Troposphere: It is the bottom layer of the atmosphere. It contains 70% mass of the atmosphere.
It extends to an average height of 14 km. However, its thickness varies from poles to equator.
The thickness of atmosphere over poles is only about 8 kms whereas its thickness above equator
is about 20 kms. In this layer the temperature decreases with height and drops to about -60o
C at
the upper troposphere. The rate at which temperature decreases with height is known as lapse
rate.
Troposphere ends at tropopause. Tropopause is just like a lid over the troposphere, where
temperature stops decreasing with height.
Stratosphere: It lies just above the tropopause. It extends to a height of 50 kms from earth’s
surface. This layer contains Ozone (O3) which prevents the harmful ultra-violet (UV) rays from
reaching the earth. This Ozone is present in the ozonosphere which is present within the
Stratosphere.
Thus, this layer acts as a protective umbrella. In this layer, temperature increases
with height and reaches from -60 degree celsius
to about 0 degrees Celsius
Above the stratosphere, temperature neither
decreases nor increases with height up to some level. This small layer is called, stratopause
which marks the end of stratosphere.
Mesosphere: It starts from the edge of the stratopause, and extends to height of 80 km from
ground. In this layer, temperature decreases with height to about -90oC.
This layer, as such does not have any impact on life. But, it gains importance as it plays crucial role in radio
communication. Just above the mesosphere lies, mesopause, in which temperature neither
decreases nor increases.
Thermosphere: It is found approximately above 80 km from earth’s surface and extends to the
edge of space. Temperature keeps rising with altitude in this layer. It is likely to reach 900 °C at
an altitude of 350 km. In this layer too, ionization of molecules take place which results in the
creation of charged ions. These layers also reflect radio waves and have influence over radio
communications. Thermosphere as such has no definable upper boundary and gradually blends
with space.
Composition of Earth’s Atmosphere:
The gaseous mantle surrounding the earth’s surface is
constituted by about 5.15 x 1015 metric tons of gas which exert a pressure of 1 kg per sq. cm. on
the surface of earth’s crust. Most of these gasses are compressed in the lower most layer due to
the pressure of layers above it. Following table shows the composition of earth’s atmosphere.
Gas (Relative percentage) [Parts per million (ppm)]
Nitrogen (78.08) [780832]
Oxygen (20.95) [209460]
Argon (0.93) [9340]
Carbon dioxide (0.03) [403]
Neon (0.0018) [18]
Ozone (0.000007) [0.07]
Importance of Atmosphere:
The atmosphere is responsible for creating the suitable conditions
for the existence of life on this planet. The atmosphere also contains some important gasses like
oxygen and carbon dioxide which are vital for the survival of animals and plants. The importance
of the atmosphere can be summed up as follows:
i) Regulation of temperature:
Atmosphere regulates the temperature of earth. The gases
present in the atmosphere are capable of absorbing the radiations of the sun and thereby
maintaining the temperature of earth. Moon on the other hand has no atmosphere. That is
why its temperature rises to about 101oC
during day and drops down to -180oC during
night.
ii) Filtration and Protection:
The incoming solar radiations contain the ultra-violet (UV)
radiations which are very harmful. These UV radiations are absorbed in the stratosphere
by the vital ozone layer. Thus atmosphere protects us from these damaging radiations.
iii) Mixing of pollutants:
Due to air currents (waves) and vertical temperature gradient,
constant mixing of gases takes place. This prevents the accumulation of harmful gases
and other pollutants at a particular spot.
iv) Weather pattern:
All weather processes occur in because of atmosphere. The gasses
present in the lower troposphere get heated. The air becomes warm and lighter. It rises up
and cools down, Cooling condenses the water vapours and results in the formation of
rain, snow etc.
B. Hydrosphere
Hydrosphere comprises all the water that is present in the oceans, seas, rivers, glaciers, snow in
the soil, rocks and in the atmosphere. This comprises all water resources both surface and ground
water. The world’s water is found in oceans and seas, lakes and reservoirs, rivers and streams,
glaciers and snow-caps in the Polar Regions in addition to ground water below the land areas.
The distribution of water among these resources is as under
Components of hydrosphere Percentage (%)
Oceans and seas 97.2
Ice caps and glaciers 2.15
Ground water 0.62
Surface water 0.03
Humans use water in the home, in industry, in agriculture, and for recreation. These
applications differ widely in the quantities and quality of water that they require. In one way or
another, we use all available sources like inland waters, ground water and ocean water. We
pollute it, re-purify it and reuse it, over and over again.
The demand for global water resources increase day-by-day though pure fresh water
availability decreases severely. Thus we should use water carefully and must appreciate its
conservation and storage.
C. Lithosphere
It is the outer boundary layer of solid earth. The outer boundary forms a complex interface with
the atmosphere and hydrosphere and is also the environment in which life has evolved. Basically
lithosphere is nothing but a crustal system composed of various layers. Various elements
constitute such crustal layer in mixture of different proportion. In general the earth crust is
composed of three major classes of rocks which include igneous rocks, sedimentary rocks and
metamorphic rocks.
There are two types of crusts
Continental crust
Oceanic crust
Interaction between the crustal system of the lithosphere and the atmosphere and the biosphere
takes place where continental crust is exposed above sea level. At the land/air interface the crust
becomes exposed to inputs of solar, radiant energy, precipitation and atmospheric gases.
Lithosphere is very important for us because we live on it, grow crops and forests, build
factories, roads, rail lines, canals etc. We get many metallic and non metallic minerals from
rocks of the earth’s crust. Many elements are present in earth’s crust as given in the table below:
Sl. No. Elements Percentage (%)
1 Oxygen 46.6
2 Silicon 27.7
3 Aluminum 8.1
4 Iron 5
5 Calcium 3.6
6 Sodium 2.8
D. Biosphere
The word ‘bios’ is an ancient Greek word meaning ‘life’. The part of the earth in which all forms
of life exist is called biosphere. Human beings form an important part of the biosphere. It
developed on earth since 4.5 billion year through evolutionary processes. Life is present at the
top layer of lithosphere, throughout the hydrosphere and into the lower atmosphere.
The size of the living organisms in the biosphere ranges from very minute microorganisms that
we cannot see with our naked eyes to huge trees and animals like the elephants on land and
whales in the ocean waters.
The biosphere is made up of distinct areas each with its own climate, soil, plant and animal
communities and these areas are called ecosystems. The biotic components interact with the
physical surroundings and also with each other.
1.3 Ecosystem
The term ecosystem was proposed by A.G. Tansley in 1935 and he defined it as the system
resulting from the integration of all the living and non-living factors of the environment.
Ecosystem is also defined as any unit that includes all the organism in a given area interacting
with the physical environment, so that a flow of energy leads to clearly defined trophic structure,
biotic diversity and material cycles within the system (Odum1971)
Kinds of ecosystem
An ecosystem can be natural or artificial, temporary or permanent, large or tiny and thus various
constituent ecosystems of the biosphere fall in following categories.
1) Natural ecosystem: These types of ecosystems operate by themselves without any major
interference by man. Based upon the particular kind of habitat, these are further categorised
as:
a) Terrestrial ecosystem:
Such as forests, grasslands, deserts, a single tree etc.
b) Aquatic ecosystem:
Which may be further distinguished as follows:
i) Fresh water ecosystem: These may be lotic (running water as spring, brook, stream
river), or lentic (standing water as lake, pond, puddle ditch, swamp etc.)
ii) Marine ecosystem: These include deep bodies such as oceans or shallow ones like
seas or estuaries etc.
2) Artificial (man engineered) Ecosystem: These are maintained artificially by man by
addition of energy and planned manipulations; natural balance is disturbed regularly.
Examples are Croplands Lake maize, wheat, and rice fields etc. where man tries to control
the biotic community as well as the physico-chemical environment.
Structure of an Ecosystem
The structure of an ecosystem is basically a description of the biotic and abiotic components of
an ecosystem.
1.3.1 Biotic or living component
Biotic component includes all plants, animals and microorganisms living in an ecosystem. The
biotic components can be classified into following groups depending on the way of obtaining
food.
a) Autotrophs: Autotrophs (auto-self, trophos-feeder) are also known as producers as they
synthesize their own food from solar energy with the help of simple inorganic substances
such as water and carbon dioxide and organic substances such as enzymes. The
autotrophs are of two types.
i) Photo-autotrophs: Which contain chlorophyll to convert the solar energy of sun into
food e.g. trees, grasses, algae, phyto-planktons, photosynthetic bacteria and
cyanobacteria (Blue green algae).
ii) Chemo-autotrophs: These are the organisms which produce their food through
oxidation of certain chemicals. They are not dependent on the solar energy e.g.
microorganisms such as Beggiatoa, Sulphur bacteria etc.
b) Heterotrophs: Heterotrophs (Heteros-Other, trophos-feeder) are the organisms which
lack the ability to synthesize their own food and have to depend on other organisms for
nutrition. They are also known as consumers because they consume the materials built up
by producers. These are further categorised as:
i) Primary consumers or herbivores: The animals which feed on the producers or
plants are known as herbivores. Examples; Sheep, cattle, deer, caterpillar etc
ii) Secondary consumers or primary carnivores: The animals which feed on the
herbivores are known as primary carnivores. Example; fox, snake etc
iii) Tertiary consumers: The animals that feed on the secondary consumers or
carnivores are known as tertiary consumers. Example; wolves etc
iv) Quaternary consumers or Top carnivores: These are the largest carnivores which
feed on the tertiary, secondary as well as primary consumers and are not eaten up by
any other animal. Example; lion and tiger
v) Omnivores: They feed on both plants and animals. Example; Man, rat, crow etc
vi) Decomposers: Decomposers are the organisms that feed on the dead organic matter
of plants and animals and break down complex organic compounds of dead
6CO2 + 6H2O + Sunlight C6H12O6 + 6O2
organisms. They are also known as reducers or saprotrophs. Example; bacteria, fungi
etc
Abiotic or Non-living component
Abiotic component of the ecosystem comprises of three components:
c) Climatic condition and physical factors of the given region: Such as pH, soil,
temperature, light, precipitation, humidity, wind etc.
d) Inorganic substances: They include water, minerals, and gases all of which are involved
in cycling of materials in the ecosystem (i.e. biogeochemical cycles). The amount of
these inorganic substances present at any given time in an ecosystem is called as the
standing state or standing quality.
e) Organic substances: Such as proteins, carbohydrates, lipids, etc. present either in the
biomass or in the environment i.e. biochemical structures that link the biotic and abiotic
component of the ecosystem.
Functions of an Ecosystem
Every ecosystem maintains itself through some functions like;
a) Food chain and food web
b) Nutrient cycling
c) Productivity (primary and secondary)
d) Energy flow
Food Chain
A food chain is a process of eating and being eaten. It is also defined a process through which
transfer of energy takes place from producers to herbivore and then to carnivores. Each food
chain is represented by a diagram including a series of arrows pointing from one species to
another.
In each step in the food chain a large portion of the energy is lost as heat. As a result, organism
in each trophic level passes on lesser energy to the next trophic level. This limits the number of
steps in any food chain to 4 or 5. Longer the food chain lesser energy is available for final
members.
A food chain is always unidirectional in nature. Examples;
a) Grassland ecosystem
Grass Grasshopper Bird Hawk
b) Pond ecosystem
Phytoplankton Zooplankton Fish Shark
Types of food chains
Grazing Food chain: This type of food chain starts from the living green plants, goes to grazing
herbivores and then to carnivores. Ecosystems with this type of food chains are directly
dependent on solar radiation. Most of the ecosystems in nature follow this type of food chain.
Detritus food chain: This type of food chain starts from dead organic matter. The food or
energy present in dead organic matter is consumed by bacteria and fungi which are then
consumed by other organisms like detritivores. This type of food chain is less dependent on the
solar energy. These food chains help in nutrient cycling. Example;
Dead organic matter Bacteria Detritivores
Food web
A single food chain never occurs in nature. There are many food chains that exist in an
ecosystem which are never independent. Many food chains are interconnected with each other to
form an interlocking pattern known as food web. The food webs provide the alternative options
of food to the organisms e.g. if a particular crop is destroyed due to some disease, the herbivores
in that area do not perish as these can graze on other crops or herbs. Greater the number of these
alternative options, more stable is the ecosystem.
Significance of food chains and food webs
a) Food chains and food webs play a very significant role in the ecosystem because the two
most important functions of energy flow and nutrient cycling takes place through them.
b) The foods chains also help in maintaining and regulating the population size of different
animals thus maintaining the ecological balance.
c) The food webs provide the alternative pathways of food availability e.g. if a particular
crop is destroyed due to some disease, the herbivores in that area do not perish as these
can graze on other crops or herbs. Greater the number of these alternative pathways more
stable is the ecosystem.
d) Food webs also help in ecosystem development.
Ecological pyramids
An ecological pyramid is a graphical representation of an ecological parameter like number or
biomass or accumulated energy at different trophic levels in a food chain in an ecosystem. The
idea of ecological pyramids was developed by Charles Elton (1927) and is also known as
Eltonian pyramid. Sometimes they are also known as food pyramids or trophic pyramids.
In ecological pyramids, the producer form the base and the successive trophic levels make up the
apex. The shape of the pyramid may be upright, inverted or irregular.
There are three types of
ecological pyramids as discussed below;
1) Pyramid of Number: It depicts the number of individuals in different trophic levels of an
ecosystem. The shape of the pyramid of number can be upright, inverted or irregular. For
example; In a grass land the producers mainly grasses are always maximum in number and then
show a decrease towards the primary consumers (herbivores) which are lesser in number than
grasses. The secondary consumers like lizards, are lesser in number than the rabbits and mice.
Finally the top (tertiary) consumers are least in number. Thus the pyramid is upright. Similar is
the case in pond ecosystem.
In a parasitic food chain the pyramid is always inverted. This is due to fact that a single plant
may support the growth of many herbivores and each herbivore in turn may provide nutrition to
several parasites which support many hyper parasites. Thus from producers to consumers the
number of organisms gradually shows an increase making the pyramid inverted in shape.
However in a forest ecosystem the pyramid of numbers is somewhat irregular in shape. The
producers mainly large sized trees, are lesser in number and form the base of pyramid. The
herbivores (fruit eating birds, elephants, deer etc.) are more in number than producers but there is
also a gradual decrease in number of successive carnivores. Thus the pyramid is upright
2) Pyramid of biomass (living matter):
The total amount of living or organic matter
present at any time in different trophic levels of an ecosystem forms the pyramid of biomass.
This is indicated by weight or other means of measuring material. In grasslands and forests, there
is generally a gradual decrease in biomass of organisms at successive levels from the producers
to the top carnivores. Thus pyramids are upright. However in a pond as the producers
are small organisms their biomass is least and the value gradually shows an increase towards the
apex of pyramid thus making the pyramid inverted in shaped.
3) Pyramid of energy:
It depicts the amount of energy trapped per unit time and area in
different trophic levels of a food chain. Pyramid of energy gives the best representation of the
trophic relationship and is always upright.
According to the second law of
thermodynamics, at each transfer 80-90% of energy available at lower trophic level is used to
perform metabolic activities and only 10% is available to next trophic level. The law of retaining
only 10% of chemical energy at each trophic level is called ten percent law. It was proposed by
Lindeman (1942).
1.3.3. Energy Flow in an ecosystem
Energy flows from one organism to another in an ecosystem in a unidirectional manner
Flow of energy in an ecosystem takes place through the food chain and it is this energy flow
which keeps the ecosystem going. The most important feature of this energy flow is that it is
unidirectional. Unlike the nutrients (like carbon, nitrogen, phosphorous) which move in a cyclic
manner, energy is not reused or recycled in the food chain.
The flow of energy in an ecosystem follows the two laws of thermodynamics;
1st Law of thermodynamics:
It states that energy can neither be created nor be destroyed but it
can be transformed from one form to another. The solar energy captured by the green plants gets
converted into biochemical energy of plants and later into that of consumers.
2nd Law of thermodynamics:
It states that energy dissipates as it is used or in other words, it
gets converted from a more concentrated form to dispersed form. As energy flows through the
food chain, there occurs dissipation of energy at every trophic level. The loss of energy takes
place through respiration, locomotion, running and other activities. At every level there is about
90% loss of energy and the energy transferred from one trophic level to the other is only about
10%.
Productivity of an ecosystem
The productivity of an ecosystem refers to the rate of production i.e. the amount of organic
matter accumulated in any unit.
1) Primary Productivity(P.P.): It is defined as the rate at which radiant energy is stored by
photosynthetic and chemosynthetic activity of producers and is of following types:
a) Gross Primary Productivity (G.P.P.): Is defined as the total rate of photosynthesis
including the organic matter used up in respiration. GPP depends on the chlorophyll
content. The rate of primary productivity is estimated as chl/g dry weight/ unit area or
photosynthetic number i.e. amount of CO2 fixed /gchl/ hour. This is also sometimes
referred to as Total (Gross) Photosynthesis or Total Assimilation.
b) Net Primary Productivity (N.P.P.): It is the rate of storage of organic matter in plant
tissues in excess of the respiratory utilisation by plants. This is thus the rate of increase of
biomass and is also known as apparent photosynthesis or net assimilation. Thus NPP
refers to balance between gross photosynthesis and respiration and other plant losses such
as death etc.
N.P.P. = G.P.P. – R
2) Secondary Productivity (S.P.): It is the rate of energy storage at consumer levels-
herbivores, carnivores and decomposers. Consumers tend to utilise already produced food
materials in their respiration and also convert the food matter into different tissues by an
overall process, so secondary productivity is not divided into gross and net. That is why some
ecologists use the term assimilation rather than production (Odum 1971) at this level. S.P in
fact remains mobile (i.e. keeps on moving from one organism to another and does not live in
situ like the primary productivity.
1.4 Ecosystem Services
Ecosystem services are the benefits people obtain from ecosystems. These include provisioning
services such as food and water; regulating services such as flood and disease control; cultural
services such as spiritual, recreational, and cultural benefits; and supporting services, such as
nutrient cycling, that maintain the conditions for life on Earth.
Economic or Provisioning Services
These are the products obtained from ecosystems, including:
Food and fibre
Fuel wood
Genetic resources.
Medicines, and pharmaceuticals
Ornamental resources
Fresh water
Ecological and Regulating Services
These are the benefits obtained from the regulation of ecosystem processes, including:
Air quality maintenance
Climate regulation
Water regulation
Erosion control
Water purification and waste treatment
Ground water recharge
Regulation of human diseases
Pollination
Storm protection
Social and Cultural Services
These are the services of the ecosystem associated with social life, customs, religion etc
Cultural diversity
Spiritual and religious values
Knowledge systems
Educational values
Inspiration
Social relations
Cultural heritage values
Recreation and ecotourism
Aesthetic and Recreation Services
Ecosystems add beauty to nature and thereby provide various aesthetic services to people. People
love spending time outdoors and appreciate natural sceneries like forests, mountains, oceans,
valleys, lakes etc. Most of us love flowers and enjoy bird watching, wild animals, big trees etc
which are nothing but aesthetic services provided by the ecosystems.
Informational Services
Ecosystems also provide an opportunity to study them and collect a lot of information and
knowledge about them. We can collect information related to plants, animals, microorganisms,
water, air etc. The various branches of science like Zoology, Botany and Geography study
animals, plants and the earth features respectively. Similarly Environmental Science explores all
the components of the ecosystem in detail.
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