General Foundation Course

( Environmental Sciences)
I Semester
NIT Delhi, Delhi

Dr. Rahul Kumar Meena

Assistant Professor
Department of Civil Engineering
 Ecosystem consists of two Words :

Eco Environment
Ecosystem
System Interaction

“An ecosystem is a group of biotic communities of species

interacting with one another and with their non-living
environment exchanging energy and matter”.
1. Introduction
• Life is a characteristic combination of physical
entities having biological processes (signaling and
self-sustaining processes).
• Various forms of life exist as - plants, animals,
fungi, protists, archaea, and bacteria.
• Human beings stand at the top in the hierarchy
of life.
• Biology is the primary science concerned with the
study of life, although many other sciences are
also involved.
2. Origin and Characteristics of Life
• Owing to its unique environment, the earth is the only planet to
harbor life.
• On the earth we can find living organisms from the poles to the
equator, from the bottom of the sea to several miles in the air, from
freezing waters to dry valleys.
• Over the last 3.5 billion years or so, living organisms on the Earth have
diversified and adopted to diverse environmental conditions.
• The diversity of life is truly amazing, but all living organisms do share
certain similarities.
• All living organisms can replicate, and the replicator molecule is DNA.
• Earlier, living organisms were divided into two kingdoms: animal and
vegetable, or the Animalia and the Plantae
• Now the most often used scheme divides all living organisms into five
kingdoms:
• Monera (bacteria),
• Protista,
• Fungi,
• Plantae,
• Animalia.
• This coexisted with a scheme dividing life into two main divisions: the
Prokaryotes (bacteria, etc.) and the eukaryotes (animals, plants, fungi,
and protists (euglena)).
• Another type of biological entities, the viruses, are not organisms in
the same sense as other living organisms are. However, they are of
considerable biological importance.
Levels of organization:
• The entire world around us is made up of
• Space,
• Matter, and
• Energy
• Space is expressed in terms of area etc. and is present
everywhere around.
• Everything around us is made up of some substances or
materials called matter. This matter is expressed in terms of
mass.
• Energy is present in the universe as an important ingredient that
makes this world functional.
• Space, matter and energy are the subject matter of various
Physical Sciences
• Atom is the lowest level of organization in the living world and non-living world
while biosphere is the highest level of organization in the living world.
• Atoms, molecules and chemical compounds are nonliving but are very important
for life.
• Cell differentiates living organisms from non living things though both are
composed of atomic and molecular assemblages. Life starts at the level of cells
which form tissues and organs.
• An organism is the first living entity for ecological studies.
• Populations, communities, ecosystems and the entire biosphere are the study area
of ecology/environmental studies.
• Each level in this hierarchy of biological organization is unique in its structure and
function and shows additional properties than those of its lower level.
• At every level there emerge some unique properties, also known as emergent
properties, which are always more than the properties of its constituent parts taken
together.
Life on the earth: Levels of organization

Living
Studied under various
biological and ecological
sciences

Non living
Studied under Physical
and Chemical sciences
• The concept of Biosphere is
like this - group of Molecules
become Cells, group of Cells
become Tissues and organs
and Organism-group of
similar organisms called
Species-group of Species
become Community-
Community and its
interactions with non living
surroundings like abiotic
factors water, soil and air
makes the Ecosystem.
• Different types of ecosystems
on the earth makes the
Biosphere.
• A group of similar organisms (i.e. belonging to the same
species) in a particular area at a particular time is called
Population.
• Number of populations (organisms of different species
taken collectively) in an area are called a community.
• An identical or distinguishable portion of the earth
containing several communities is called a biome.
• Entire zone on earth consisting of living organisms is
known as Biosphere.
• Biosphere along with its environment is called
Ecosphere.
3. Ecosystem
• Life does not exist in space or
isolation . It needs a substratum
which provides space, necessary
substances and favorable
conditions for living organisms .
• In an area, the community of
living organisms interacts with its
physical environment to form a
definite structural and functional
system .
• This structural and functional unit
of life in nature is called an
Ecological System or simply an
Ecosystem.
• The term ecology has been derived from a Greek word
• ‘oikos’ (Oikos=household/habitat; logos=study).
• The word “ecology” (“Ökologie”) was coined in 1866 by
the German scientist Ernst Haeckel.
• It relates to the scientific study of organisms or groups
of organisms in their natural habitat.
• The science of ecology is often categorized as a branch of
biosciences that studies the interactions among
organisms and their environment, or the interactions
organisms have with each other and with their abiotic
environment.
• An ecosystem is a spatial and organizational unit which is formed
by the interactions of living organisms with each other and with
their physical environment.
• Thus, the community of living organisms (plants, animals and
microorganisms) in any area taken together with their non-living
environmental components (such as soil, air and water) forms an
ecosystem.
➢ A pond, grassland, garden, forest, etc are the common examples
of ecosystem. The earth’s living organisms interacting with their
physical environment (i.e., biosphere) may be considered as a giant
and vast ecosystem.
➢ On the contrary a small pool of water containing certain forms of
living organisms (such as plants, insects, microorganisms, etc) may
also be regarded as an ecosystem.
• The term “ecosystem” was first used by a British ecologist ‘Arthur Tansley’ in
1935. He explained the concept of ecosystem which can be summarized as:
• When both, biotic and abiotic components are considered, the basic
structural and functional units of nature are ecosystems.
• There exist varying degrees of positive or negative or even neutral
interactions among organisms at both interspecific and intraspecific levels
(within the members of same species or between the members of different
species).
• Energy is the driving force of this system. Energy flow is unidirectional and
noncyclic.
• There operate biogeochemical cycles in the ecosystem. This movement of
nutrients within an ecosystem is always cyclic.
• The limiting factors of environment govern the successful growth of
organisms. Under natural conditions, different kinds of populations undergo
succession.
A. Types of ecosystems: In a simpler way
ecosystems can broadly be categorized as under:

1. Natural ecosystems: all the naturally occurring

ecosystems where man’s interruption is thought
mainly to be unwarranted such as a forest, grassland,
river, etc.
2. Artificial ecosystems: all the ecosystems which are
created and managed by man such as a cropland, a
garden, a pond, etc
Natural ecosystem
1. Terrestrial ecosystems: all the ecosystems on land such
as a forest, a desert, grassland, a cropland, etc.
2. Aquatic ecosystems: all the ecosystems where the
dominant factor is water such as a pond, a lake, a river,
a spring, a lake, a sea, an ocean, etc.
Structure of an Ecosystem

● Characterized by the
organization of biotic and
abiotic components.
● Includes the distribution
of energy and climatic
conditions.
Biotic Components

● Living organisms that

interact with each other
and the environment.
● Includes plants, animals,
and microorganisms.
● Essential for the
functioning of the
ecosystem.
Abiotic Components

● Non-living components
that interact with biotic
components.
● Includes air, water, soil,
sunlight, and temperature.
● Also essential for the
functioning of the
ecosystem.
3. Ecosystem
• Life does not exist in space or
isolation . It needs a substratum
which provides space, necessary
substances and favorable
conditions for living organisms .
• In an area, the community of
living organisms interacts with its
physical environment to form a
definite structural and functional
system .
• This structural and functional unit
of life in nature is called an
Ecological System or simply an
Ecosystem.
• An ecosystem is a spatial and organizational unit which is formed
by the interactions of living organisms with each other and with
their physical environment.
• Thus, the community of living organisms (plants, animals and
microorganisms) in any area taken together with their non-living
environmental components (such as soil, air and water) forms an
ecosystem.
➢ A pond, grassland, garden, forest, etc are the common examples
of ecosystem. The earth’s living organisms interacting with their
physical environment (i.e., biosphere) may be considered as a giant
and vast ecosystem.
➢ On the contrary a small pool of water containing certain forms of
living organisms (such as plants, insects, microorganisms, etc) may
also be regarded as an ecosystem.
A. Types of ecosystems: In a simpler way ecosystems can broadly be categorized as
under:

1. Natural ecosystems: all the naturally occurring

ecosystems where man’s interruption is thought
mainly to be unwarranted such as a forest, grassland,
river, etc.
2. Artificial ecosystems: all the ecosystems which are
created and managed by man such as a cropland, a
garden, a pond, etc
Natural ecosystem
1. Terrestrial ecosystems: all the ecosystems on land such
as a forest, a desert, grassland, a cropland, etc.
2. Aquatic ecosystems: all the ecosystems where the
dominant factor is water such as a pond, a lake, a river,
a spring, a lake, a sea, an ocean, etc.
 Various types of ecosystems
ECOSYSTEMS

Natural Artificial
e.g. Garden, crops,
aquarium, Farmland etc.
Aquatic Terrestrial

Fresh Water Grassland Desert Forest

Marine
Lentic Lotic Wetlands
e.g. e.g. e.g. Coastal Upwellin Open
ponds, rivers, marshes, Areas g Oceans
lakes streams swamps e.g. Regions
estuaries,
coral reefs,
mangroves
Schematic representation - Structural aspects of an ecosystem
 I. Abiotic Components
• It is the portion of an ecosystem that is non living. Rocks,
soil, gases, water, temperatures, winds, other forces, etc.
are abiotic component of ecosystem.
• It is, thus, also said to be the aggregate of environmental
factors and includes:
• Climatic factors such as rainfall, humidity, temperature,
light.
• Topographic factors such as altitude, slope, direction of
mountain ranges etc.
• Edaphic factors such as soil composition, soil texture,
soil biota etc.
• These abiotic components/environmental factors in an
ecosystem are capable of bringing marked distributional,
structural and functional changes in organisms.
• An organism requires harmonious relationship with its immediate
environment for its proper growth, reproduction, etc.
• The difference between the types of vegetation or consumers of
a desert and a rain forest indicates the role of environmental
factors on the distribution and survival of organisms in different
ecosystems.
• These environmental factors exhibit diurnal, seasonal, annual
and cyclic variations to which the organisms are subjected.
II. Biotic Components
• Biotic components are the living entities in an ecosystem. They include all the
microbes, animals, plants and their products. They can be categorized as:
a) Producers or Autotrophic components: These are the producers which convert
simple inorganic substances into complex organic substances with the help of
solar energy. They are of two types:
(i) Photosynthetic: They manufacture food with the help of chlorophyll in
presence of sunlight so energy utilized is radiant energy. These constitute the
major proportion of autotrophic components. It includes green plants, green
algae and photosynthetic bacteria.
(ii) Chemosynthetic: They manufacture food with the help of chemical energy
evolved during chemical reactions (chemosynthesis). They contribute to lesser
extent to the production of food in an ecosystem. It includes mostly bacteria,
certain archaea etc.
• In ecosystems we generally consider only green plants as producers as they
manufacture their food by using energy from the sun. In the sea these include
tiny algal forms to large seaweeds.
b) Consumers or Heterotrophic components: They consume the
food produced by the producers. They are of following types.
(i) Macro consumers: These are the consumer organisms which
are of larger size and feed upon the producers. Based upon their
position in the food chain they can be categorized in primary,
secondary and tertiary consumers.
• Primary consumers (Herbivores): Eat producers such as green
plants eg. Deer, goat, grasshopper, etc.
• Secondary consumers (Smaller carnivores): eats herbivores
(animals) eg. Snake, eagle, lizard, large fish, etc.
• Tertiary consumers (Larger carnivores): Eats smaller carnivores
eg. Lion, hawk, tiger, man, etc
(ii) Micro-consumers or Decomposers:
• Decomposers are a group of organisms consisting of small
animals like worms, insects, bacteria and fungi, which break
down dead organic material into smaller particles and finally into
simpler substances that are used by plants as nutrition.
• Decomposition thus is a vital function in nature, as without
this, all the nutrients would be tied up in dead matter and no
new life could be produced.

In simpler terms biotic component of ecosystem consists of

producers (green plants), consumers (herbivore and carnivore
animals) and decomposers (microorganisms).
Habitat and Niche
● Habitat refers to the physical
environment in which an organism
lives.
● Niche represents the specific role and
position of an organism within an
ecosystem.
● Includes the organism's interactions
with other species, resource
utilization, and response to
environmental conditions.
Importance of Ecosystem Components

● All the components of an

ecosystem work together to create
a sustainable environment.
● Each component is essential for
the functioning of the ecosystem
and the survival of the organisms
within it.
Functions of Ecosystem
● Regulates essential ecological
processes and supports life
systems
● Responsible for the cycling of
nutrients between biotic and
abiotic components
● Maintains a balance among the
various trophic levels in the
ecosystem
● Cycles minerals through the
biosphere
Productivity

● Refers to the rate of

biomass production
● Measures the amount of
energy stored in vegetation
● Determines the carrying
capacity of an ecosystem
 Mainly three types of consumers
i. Herbivores
ii. Carnivores
iii. Omnivores
Producers

 Producers make their

own food.
 Green plants use
energy from the sun
to prepare food.
 Producers are on the
bottom of the food
chain.
Consumers
 Organisms that do not make their own food.
 Another term for heterotroph is consumer because
they consume other organisms in order to live.
Herbivores
Carnivores
Omnivores
Decomposers
 Microorganisms that are able to break down large
molecules into smaller parts.
 Decomposers return the nutrients that are in a living
thing to the soil.
ex. Bacteria
Fungi
Energy Flow
● Sequential process through which
energy flows through the ecosystem
● Captured from the sun and travels
from producers to consumers then
decomposers
● Returns to the environment in the
form of heat and light
 The sun is the biosphere's sole source of energy. Solar energy travels in the
form of electromagnetic waves. It comprises of a diverse variety of
wavelengths and radiation types (infra red, visible, ultra violet, etc.).
 The producers use only a fraction of the sun's electromagnetic spectrum. The
quantity of solar energy that reaches a surface perpendicular to the sun's rays
in the outer atmosphere is known as the solar constant. This equates to 2.00
calories per square centimetre each minute. About 1.00cal/sq.cm/min of this
quantity reaches the earth's surface.

 Various energy flow models can explain the movement of energy via various
trophic levels in an ecosystem.
 CONCEPT OF ENERGY IN
ECOSYSTEM
 Energy is the capacity to do work.
 Biological activities require consumption of energy
which ultimately comes from sun.
 Except for the deep-sea hydrothermal ecosystem,
sun is only the source of energy for all ecosystem on
Earth.
 Of the total incident solar radiation less than 60% is
photosynthetically active radiation (PAR).
 Solar energy of sun is transformed into chemical
energy(Adenosine triphosphate) by the process of
photosynthesis, then it is stored in plant tissues and
then transformed into mechanical and heat form of
energy during metabolic activities.
 Components of the energy flow in
Ecosystem-Sun
 Sun - The energy used for all plant life processes is
derived from solar radiations and all animals are further
dependent on plants. About 34% of the sunlight
reaching the Earth's atmosphere is reflected back (by
clouds and dust), 10% is held by ozone layer, water
vapour and other atmospheric gases. The rest 56%
reaches the earth's surface and out of that only 2 to
10% is used by plants and the remaining is absorbed as
heat by water or ground.
 Components of the
energy flow in
Ecosystem-Producers
 Producers - The green plants in the
ecosystem-terminology are called
producers. In a terrestrial ecosystem major
producers are herbaceous and woody
plants. Likewise, primary producers in an
aquatic ecosystem are various species like
phytoplankton, algae and higher plants.
Components of the energy
flow in Ecosystem-
Consumers
 Consumers – All animals depend on
plants (directly or indirectly) for their
food needs. Hence, they are called
consumers and also heterotrophs.
 Components of the
energy flow in Ecosystem-
Consumers
 Decomposers - The heterotrophic
organisms, mainly fungi and bacteria,
which meet their energy and nutrient
requirements by degrading dead organic
matter or detritus are called
decomposers. They are also known as
saprotrophs.
FOOD CHAIN & FOOD WEB
A. Food Chain:
• The sequence of eating and being eaten in an ecosystem is
known as food chain.
• All organisms, living or dead, are potential food for some
other organism and thus, there is essentially no waste in the
functioning of a natural ecosystem.
• A caterpillar eats a plant leaf, a sparrow eats the caterpillar, a
hawk eats the sparrow, and when they all die, they are all
consumed by microorganisms like bacteria or fungi.
• Food chains usually have two to six links (or trophic levels in
an ecosystem).
• In nature, we come across two major types of food chains as
below:
(i) Grazing food chain:
• It starts with green plants and
culminates in carnivores.
• Some examples are
• grass → grasshopper → frog →
snake → hawk(grassland
ecosystem)
• grass → rabbit → fox
• phytoplanktons → water fleas
→ small fish → tuna (pond
ecosystem)
• phytoplanktons →
zooplanktons → fish
• lichen → riendeer → man
(Arctic region)
Grazing food chains
(ii) Detritus food chain:
• It starts with dead organic matter which the detritivore and
decomposers consume.
• Partially decomposed organic matter and even the
decomposers are fed upon by the detritivores. A detritivore is
an organism that eats dead or decaying plants or animals as food.
Detritivores include microorganisms such as bacteria and larger
organisms such as fungi, insects, worms, and some crustaceans.
• Some examples are:
• Leaf li er → algae → crabs → small carnivorous fish → large
fish (mangrove ecosystem)
• Dead organic ma er → fungi → bacteria (forest ecosystem)
• Dead grass → termite → aardvark (grassland ecosystem)
Detritus food chain:
(iii) Parasitic food chain:
• Parasites which derive nutrition from other plants and animals
also constitute a link in yet another type of food chain which may
be designated as Parasitic food chain.
• It may commence at any level in a trophic structure and may at
times result in heavy losses of energy.
B. Food web:
• In natural ecosystems food chains rarely operate as isolated linear
sequences. They are found to be interconnected and forming a
complex network of several food chains together at the same time.
• Food web is, thus, a network of food chains where different types
of organisms are connected at different trophic levels, so that there
are a number of options of eating and being eaten at each trophic
level.
✓ For example, in grazing food chain of a grassland, in the absence
of rabbit, grass may be eaten by mouse.
The mouse in turn may be eaten directly by hawk or by snake
which is then eaten by hawk.
• In such a food web there may be seen as many as five linear food
chains.
 • grass → grasshopper → hawk
• grass → grasshopper → lizard →
hawk
• grass → rabbit → hawk(or vulture
or fox or even man , if present)
• grass → mouse → hawk
• grass → mouse → snake → hawk
✓ Food webs are very important in
maintaining the stability of an
ecosystem in nature.
Introduction to food chain
FOOD CHAIN
A food chain is the
path by which
energy in the
form of food,
passes from one
living thing to
another within
the ecosystem
 Tropic levels in the food chain
Mainly three tropic levels in food chain

 Producers
 Consumers
 Decomposers
Producers
 Producers make their
own food.
 Green plants use
energy from the sun
to prepare food.
 Producers are on the
bottom of the food
chain.
Consumers

 Organisms that do not make their own food.

 Another term for heterotroph is consumer because
they consume other organisms in order to live.
CONCEPT OF ENERGY IN ECOSYSTEM
• Energy is the capacity to do work.
• Biological activities require consumption of energy
which ultimately comes from sun.
• Except for the deep-sea hydrothermal ecosystem, sun
is only the source of energy for all ecosystem on Earth.
• Of the total incident solar radiation less than 60% of it
is photosynthetically active radiation (PAR).
• Solar energy of sun is transformed into chemical
energy(Adenosine triphosphate) by the process of
photosynthesis, then it is stored in plant tissues and
then transformed into mechanical and heat form of
energy during metabolic activities.
• Plants capture only 2 to 10 % of the PAR and this small amount of energy sustains the entire living world!
• So, it is very important to know how solar energy captured by plant flows through different organisms of an
ecosystem.
• This can be shown by the following schematic diagram - HEAT ENERGY
RADIANT ENERGY
PRODUCERS
CHEMICAL ENERGY CONSUMERS
SUN (metabolism)
(metabolism)

DECOMPOSERS
(metabolism)

HEAT ENERGY

HEAT ENERGY
THE TEN PERCENT LAW

• This law was introduced in context to energy flow

in ecosystems by Raymond Lindeman.

• According to this law, during the transfer of

energy from organic food from one tropic level to
the next, only ten percent of the energy from
organic matter is stored as flesh.

• The remaining is lost during transfer, broken

down in respiration, or lost to incomplete
digestion by higher trophic level.
• The ten percent law gives us a basic understanding on the cycling of food chains.
• Furthermore, this law shows the inefficiency of energy capture at each successive tropic level.
REPRESENTATION OF ENERGY FLOW IN ECOSYSTEM
• Tropic level – Organisms occupy a place in the natural surroundings or in a community according
to their feeding relationship with other organisms. Based on the source of their nutrition or food,
organisms occupy a specific place in the food chain that is known as their tropic level. A given
organism may occupy more than one tropic level simultaneously.
• Organisms at each tropic level depend on those at the lower tropic level for their energy demands.
• Standing crop - Each tropic level has a certain mass of living material at a particular time called as
the standing crop. It is measured as the biomass of an organism or their number in a unit area.
• Pyramid of energy - Any calculations of energy content, biomass, or numbers has to include all
organisms at that tropic level.

Tertiary consumer 10 J

Secondary consumer 100 J

Primary consumer 1000 J

Primary producer 10,000 J

 CONCLUSION

• An ecosystem is a functional unit with energy flowing among its abiotic components
very efficiently.
• Energy flow in an ecosystem is always unidirectional.
• Energy in an ecosystem is never destroyed but it is converted from one form to another.
• Only 10 % of energy is passed to the successive tropic level.
• Sun is the ultimate source of energy.
• Plants play a vital role in converting the solar energy to the chemical energy, making
the sun’s energy available to the organisms at higher tropic levels.
• If any of the link in a food chain or food web (interconnected food chains) is removed
efficient energy flow will not occur.
Introduction to food webs
 A number of food
chains form a
interlinking pattern
forming a web like
arrangement known
as food web.
Ecological pyramids
 The pyramidal representation of tropic levels
different organisms based on their ecological
position [producer to final consumer] is called as
an ecological pyramids.
Types of pyramids
 Mainly three types of pyramids

1) Pyramid of number
2) Pyramid of biomass
3) Pyramid of energy
C. Ecological pyramids:
• Graphic representation of trophic structure and function of an
ecosystem, starting with producers at the base and successive
trophic levels forming the apex is known as an ecological pyramid.
• The concept of ecological pyramid was developed by Charles Elton
after whose name these pyramids are also known as Eltonian
pyramids.
✓ There are three types of ecological pyramids
i. Pyramid of Numbers:
➢ It represents the number of individuals at each trophic level.
➢ We may have upright or inverted pyramid depending upon the
type of ecosystem and food chain considered.
• Ecosystems like a grassland or a pond show an upright pyramid
of numbers
• The producers in a grassland are the
grasses and that in a pond are
phytoplanktons (algae etc.) which are
small in size but very large in number. So
they (producers) form a broad base.
Upright pyramid of number as in a
grassland or pond.
• The herbivores in grassland are insects
while tertiary carnivores are hawk or
other birds which are lesser and lesser in
number and hence the pyramid apex
becomes narrower and form an upright
pyramid.
• Similarly in a pond ecosystem, herbivores,
carnivores and top carnivores decrease in
number at higher trophic levels. Upright pyramid of number as in a
grassland or pond
• In a forest ecosystem, big trees are producers, which are less in
number and hence form a narrow base.
• A large number of herbivores including birds, insects and several
species of animals feed upon the trees (on leaves, fruits, flowers, bark
etc) and form a much broader middle level.
• The secondary consumers like fox, snakes, lizards, etc. are less in
number than herbivores while top carnivores (like lion, tiger, etc) are
still lesser in number.
• Parasitic food chains show
inverted pyramids.
• The producers like a few big
trees harbor fruit eater birds
which are large in number.
• A much higher number of lice,
bugs etc grow as parasite on
these birds while a still greater
number of hyperparasites like
bugs, fleas, microbes, etc feed
upon them thus making an
inverted pyramid. Inverted pyramid as shown
in parasitic food chains
Inverted pyramid of number in a parasitic
food chain
ii. Pyramid of Biomass:
• Biomass- Is the mass of living biological organisms in a given area
or a ecosystem at a given time. It can be expressed as average
mass per unit area.
• Pyramid of biomass is based upon the total biomass at each
trophic level in a food chain.
• The pyramid of biomass can also be upright or inverted.
• The pyramid of biomass in a forest ecosystem is upright in
contrast to its pyramid of numbers where it is Dimond shape.
• This is because the producers accumulate a huge biomass while
the consumer’s total biomass declines at higher trophic levels.
• The pond on the other hand shows an inverted pyramid of
biomass. The total biomass of producers is much less than that of
herbivores and it goes on increasing towards higher trophic
levels.
Pyramid of Biomass (up right)
iii. Pyramid of Energy:
• The amount of energy present
at each trophic level is
considered for this type of
pyramid.
• This type of pyramid gives the
best representation of the
trophic relationship and it is
always upright.
• At every successive level there
is a huge loss of energy (about
90%) in the form of heat,
respiration, etc. thus at each
next higher level only 10% of
the energy passes on. Hence
there is a sharp decline in
energy level of each
successive trophic level as we
move from producers to top
carnivores.
Upright pyramid of Energy
D. Functional aspects of an ecosystem:
• An ecosystem works as a unit in an efficient and organized way. It
receives energy from the sun and passes it on through its components
and, in fact, all life depends on this flow of energy.
• Green plants (including phytoplanktons) alone are able to trap the solar
energy in an ecosystem. They make use of this energy for their growth
and maintenance. Energy gets stored as chemical bonds of large organic
molecules in green plants.
• Heterotrophs or consumers obtain their energy requirements from this
stored energy (in green plants) as food and use it for their
development, growth, maintenance or other life activities.
• All life forms in an ecosystem are linked together by the flow of energy.
Besides energy, various nutrients and water, which are also required
for life processes, are exchanged by the biotic components within
themselves and with their abiotic components.
• The flow of energy and nutrients in an ecosystem keeps it going on. This
mechanism can be studied in a simplified manner as under.
Ecosystem Energetics
• As stated above an ecosystem needs energy inputs from outside. Materials are used from
within an ecosystem.
• Flow of energy in an ecosystem takes place through food chains and it is this energy flow
which keeps the ecosystem going on. Most important feature of this flow is that it is
unidirectional.
• Unlike the nutrients which move in a cyclic manner and are reused by the producers after
flowing through the food chain, energy is not reused in the food chain. Flow of energy
follows the laws of thermodynamics.
i. First law of thermodynamics states that the 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 is converted into biochemical energy of plants and latter into that of
consumers.
ii. Second law of thermodynamics states that energy dissipates as it is used or in other
words, it gets converted from concentrated to dispersed form. As energy flows through the
food chains, there occurs dissipation of energy at every trophic level. At each trophic level,
about 90% of energy gets lost and only 10% of it gets transferred to the next level.
Energy Flow in Ecosystem
• As mentioned above the sun is the only source of energy for the entire
biosphere. Solar energy travels in electromagnetic waves form. It consists of a
wide range of wavelengths and various types of radiations (infra red, visible, ultra
violet, etc.).
• Only a specific portion of sun’s electromagnetic spectrum is utilized by the
producers. The amount of solar energy reaching a surface perpendicular to the
sun rays at outer atmosphere is called solar constant. This is 2.00 calories per sq
cm per minute. Of this quantity about 1.00cal/sq.cm/min reaches the earth’s
surface.
• The flow of energy through various trophic levels in an ecosystem can be
explained with the help of various energy flow models.
 Ecological Succession
Succession is a gradual process in which structure of an ecosystem
gets changed over time.
Ecosystems are not static in nature. They are always in a state of
change and dynamism.
It is actually the structure of biotic community that evolves in the
process. They change themselves in accordance with the prevalent
environmental conditions. These changes are very orderly and
predictable.
It is seen that at a particular place a particular community of
organisms is totally replaced by another over a period of time.
Ecological succession can be defined as an orderly process of
changes in the structure and function of a community in ecosystem with
time mediated by modifications in environmental complex.
Each species is adapted to thrive and compete best against
other species under a very specific set of environmental
conditions. If these conditions change, then the existing
species will be outcompeted by a different set of species
which are better adapted to the new conditions.
“Survival of the fittest”
Change in the plant species present in an area is one of the
driving forces behind changes in animal species. This is
because each plant species will have associated animal
species which feed on it.
The presence of these herbivore species will then dictate
which particular carnivores should be present. Likewise,
the microbial communities are also influenced by the plant
and animal communities present at a particular place.
 Types of succession:
A. Primary succession:
 It occurs in essentially lifeless areas—regions in which the soil is
incapable of sustaining life as a result of such factors as lava flows,
newly formed sand dunes, or rocks left from a retreating glacier.
B. Secondary succession:
 It occurs in areas where a community that previously existed has
been removed; it is typified by smaller-scale disturbances that do
not eliminate all life and nutrients from the environment.
C. Autogenic Succession:
If the existing community itself causes its replacement by some
other community.
D. Allogenic succession:
✓ If the existing community is replaced by another community due
to some external force.
E. Autotrophic succession:
✓ Here the early and continued dominants are autotrophs. There
is gradual increase in the organic matter content supported by
energy flow.
F. Heterotrophic succession:
✓ Here early dominants are heterotrophs. There is progressive
decline in energy content.
 Causes of Succession:
• There are three major causes of succession:
A. Initial or initiating causes: These are climatic as well as biotic. Climatic
factors include erosion and deposits, wind, fire etc caused by lightening
or volcanic activity and biotic include various activities of organisms.
These causes produce bare areas or destroy the existing populations in
an area.
B. Ecesis (continuing) causes: These are the processes as migration, ecesis,
aggregation, competition reaction etc which cause successive waves of
populations as a result of changes chiefly in the edaphic features of the
area.
C. Stabilizing causes: These cause the stabilization of the community.
Climate of the area is the chief cause of stabilization.
Forest Ecosystem:
• A forest is a natural terrestrial ecosystem where the trees, shrubs, climbers and
ground flora in plants and several groups of mammals, birds, reptiles and
microorganisms in animals predominantly form the structure the biotic
community.
• Each forest type forms a habitat for a specific community of animals that are
adapted to live in it.
• The types of forests present in a particular geographic region are determined by
the environmental conditions prevalent in that region.
• Forests on the mountains and hills differ from those along the river valleys.
Similarly in the type of vegetation and the animal communities vary from forest
to forest.
• In India, for instance, the coniferous tree specis occur in the Himalayas,
mangrove trees in river deltas and the thorn trees and bushes grow in the arid
regions.
• Likewise among animals, the snow leopard, wild sheep and goats live in the
Himalayas while the leopard and tiger are found in the forests of the rest of
India.
 Like any other ecosystem a forest ecosystem consists
structurally of two components.

a. Abiotic component:
It consists of the physical environment of a forest including climatic and
edaphic (soil) conditions. Climatic conditions such as precipitation,
temperature, etc. differ from place to place and so do the forest types.
Forest soil is very rich in humus or organic matter and it differs from
other types of soil.
b. Biotic component:
✓ It includes various groups of plants, animals and microorganisms.
Plants include the trees, shrubs, climbers, grasses, and herbs in the
forest. These include species that flower (angiosperms), and non-
flowering species (gymnosperms) such as ferns, bryophytes, fungi and
algae.
✓ Trees are the dominant vegetation group in a forest. The animals
include species of mammals, birds, reptiles, amphibians, insects and
other invertebrates.
 Depending upon the climatic conditions
forests can be of different types:

1. Tropical Rain Forest

2. Tropical Deciduous forests
3. Tropical Scrub Forests
4. Temperate Rain Forests
5. Temperate Deciduous
Forests
6. Evergreen Coniferous
Forests
Depending upon the prevailing climatic conditions
forests can be of various types:

i. Tropical Rain Forests:

• They are evergreen broadleaf forests found near the equator.
• They are characterized by high temperature, high humidity and high rainfall, all
of which favour the growth of trees.
• They are the richest in biodiversity.
• We come across different types and layers of plants and animals in the tropical
rain forests. e.g. the emergent layer is the topmost layer of the tallest broad-
leaf evergreen trees, below which lies the canopy where top branches of
shorter trees form an umbrella like cover. Below this is present the understory
of still smaller trees. On the tree trunks some woody climbers are found to
grow which are known as Lianas.
• There are some other plants like Orchids which are epiphytes i.e. they are
attached to the trunks or branches of big trees and they take up water and
nutrients falling from above and can hold 4 litres of water.
• Thus, these epiphytes almost act like mini-ponds suspended up in the air, in the
forest crown. That is the reason why a large variety of birds, insects and animals
like monkeys have made their natural homes (habitats) in these forests.
• The under storey trees usually receive very dim sunlight. They usually develop
dark green leaves with high chlorophyll content so that they can use the diffused
sunlight for photosynthesis.
• The shrub layer receives even less sunlight and the ground layer commonly
known as forest floor receives almost no sunlight and is a dark layer.
• Most of the animals like bats, birds, insects etc. occupy the bright canopy layer
while monkeys, toads, snakes, chameleons etc. keep on moving up and down in
sunny and darker layers.
✓ The Silent Valley in Kerala is the only tropical rain forest lying in India which is the natural
habitat for a wide variety of species. Being the store-house of biodiversity, the forests provide
us with an array of commercial goods like timber, fuel wood, drugs, resins, gums etc.
ii. Tropical deciduous forests:
• They are found a little away from the equator and are
characterized by a warm climate the year round. Rain occurs only
during monsoon.
A large part of the year remains dry and therefore different types of
deciduous trees are found here, which lose their leaves during dry
season.
iii. Tropical scrub forests:
• They are found in areas where the dry season is even longer. Here
there are small deciduous trees and shrubs.
iv. Temperate rain forests:
• They are found in temperate areas with adequate rainfall. These are
dominated by coniferous trees like pines, firs, redwoods etc. They also
consist of some evergreen broad-leaf trees.
v. Temperate deciduous forests:
• They are found in areas with moderate temperatures. There is a
marked seasonality with long summers, cold but not too severe
winter and abundant rainfall throughout the year. The major trees
include broad leaf deciduous trees like oak, hickory, poplar etc.
vi. Evergreen coniferous forests (Boreal Forests):
• They are found just south of arctic tundra. Here winters are long,
cold and dry. Sunlight is available for a few hours only.
• In summer the temperature is mild, sun-shines for long hours but
the season is quite short. The major trees include pines, spruce,
fir, cedar etc. which have tiny, needle shaped leaves having a
waxy coating so that they can withstand severe cold and drought.
• The soil is found to get frozen during winter when few species
can survive. The leaves, also known as needles, fall on the forest
floor and cover the nutrient poor soil.
• These soils are acidic and prevent other plants from growing.
Species diversity is rather low in these forests.
Forest types in India:
• Forests in India can broadly be divided into two main categories viz.,
Coniferous forests and Broadleaved forests.
✓ They can also be classified according to the nature of their tree species –
evergreen, deciduous, xerophytic or thorn trees, mangroves, etc.
✓ They, sometimes, may also be classified according to the most abundant
species of trees such as Sal, Teak, Oak, Pine, Deodar or Chinar forests.
• Coniferous forests grow in the Himalayan mountain region, where the
temperatures are low. These forests have tall stately trees with needle like
leaves and downward sloping branches so that the snow can slip off the
branches.
• Broadleaved forests have several types, such as evergreen forests, deciduous
forests, thorn forests, and mangrove forests. Broadleaved forests have large
leaves of various shapes.
Grassland ecosystem:
• Grassland ecosystem the grasses and shrubs form the dominant part of
vegetation. It grows in areas where rainfall is usually low and the soil depth
and quality is poor.
• A variety of grasses, herbs, and several species of insects, birds and
mammals have evolved so that they are adapted to these wide-open grass
covered areas.
➢ Three types of grasslands are found to occur in different climatic regions:
i. Tropical grasslands:
• They occur near the borders of tropical rain forests in regions of high average
temperature and low to moderate rainfall.
• In Africa, these are typically known as Savannas, which have tall grasses with
scattered shrubs and stunted trees. The Savannas have a wide diversity of
animals including zebras, giraffes, gazelle, antelopes etc.
• Fires are quite common during dry season. Termite mounds are very common
here. Tropical savannas have a highly efficient system of photosynthesis. Most
of the carbon assimilated by them in the form of carbohydrates is in the
perennating bulbs, rhizomes, runners etc. which are present underground.
• Deliberate burning of these grasslands can release huge quantities of carbon
dioxide, a green house gas, responsible for global warming.
ii. Temperate grasslands:
• They are usually found on flat, gentle sloped hills, winters are very cold but
summers are hot and dry. Intense grazing and summer fires do not allow
shrubs or trees to grow.
• In the United States and Canada these grasslands are known as prairies, in
South America as Pampas, in Africa as Velds and in central Europe and Asia
they are known as Steppes. Winds keep blowing and evaporation rate is very
high. It also favours rapid fires in summer. The soils are quite fertile and
therefore, very often these grasslands are cleared for agriculture.
iii. Polar grasslands (Arctic Tundra):
• They are found in arctic polar region where severe cold and strong, frigid
winds along with ice and snow create too harsh a climate for trees to grow.
• In summers the sun-shines almost round the clock and hence several small
annual plants grow in the summer.
• The animals include arctic wolf, weasel, arctic fox, reindeer etc. A thick
layer of ice remains frozen under the soil surface throughout the year and
is known as permafrost.
• In summer, the tundra shows the appearance of shallow lakes, bogs etc.
where mosquitoes, different type of insects and migratory birds appear.
Grassland Types in India
• Grasslands form a variety of ecosystems that are located in
different climatic conditions ranging from near desert conditions to
moist conditions.
• The Himalayan pasture belt extends up to the snowline. These
Himalayan pastures have a large variety of grasses and herbs.
Himalayan hill slopes are covered with thousands of colourful
flowering plants. There are also a large number of medicinal plants.
The patches of tall elephant grass, which grows to a height of about
five meters, are located in the low-lying waterlogged areas.
• Himalayan wildlife requires both the forest and the grassland
ecosystem as important parts of their habitat. The animals migrate
up into the high altitude grasslands in summer and move down into
the forest in winter when the snow covers the grassland.
• The Semi-arid plains of Western India, Central India and the
Deccan are covered by grassland tracts with patches of thorn
forest. Several mammals such as the wolf, the blackbuck, the
chinkara, and birds such as the bustards and floricans are
adapted to these arid conditions.
• The Scrublands of the Deccan Plateau are covered with seasonal grasses
and herbs on which its fauna is dependent. It is teaming with insect life on
which the insectivorous birds feed.
• The grasses are the major producers of biomass in these regions. Each
grassland ecosystem has a wide variety of species of grasses and herbs.
Desert Ecosystem:
• A desert is an arid or semi arid area with very low annual rainfall and
sparse patches of vegetation.
• Desert ecosystems witness very extreme climatic conditions, either too
hot as in Thar desert or too cold as in Ladakh.
• Deserts occupy one-fifth of the Earth’s land surface. These ecosystems
occur in regions where evaporation exceeds precipitation (rainfall, snow
etc.).
• The precipitation is less than 25 cm per year. Deserts have little species
diversity and consist of drought resistant or drought avoiding plants. The
atmosphere is very dry and hence it is a poor insulator. That is why in
deserts the soil gets cooled up quickly, making the nights cool.
Deserts are of three major types, based on
climatic conditions:
i. Tropical deserts
like Sahara and Namib in Africa and Thar desert
Rajasthan, India are the driest of all with only a few
species.
ii. Temperate deserts
like Mojave in Southern California where day time
temperatures are very hot in summer but cool in
winters.
iii. Cold deserts
like the Gobi desert in China and High altitude cold
desert in Ladakh have cold winters and warm
summers.
• Desert plants and animals show most typical adaptations for
conservation of water.
• Many desert plants are found to have reduced, scaly leaves so as to cut
down loss of water due to transpiration or have succulent leaves to store
water.
• Many a times their stems get flattened and develop chlorophyll so that
they can take up the function of photosynthesis.
• Some plants show very deep roots to tap the groundwater. Many plants
have a waxy, thick cuticle over the leaf to reduce loss of water through
transpiration.
• Desert animals like insects and reptiles have thick outer coverings to
minimize loss of water. They usually live inside burrows where humidity
is better and heat is less. Desert and semi arid regions have a number of
highly specialized insects and reptiles.
• The rare animals include the Indian wolf, desert cat, desert fox
and birds such as the Great Indian Bustard and the Florican.
Some of the commoner birds include partridges, quails and sand
grouse.
• Desert soil is rich in nutrients but deficient in water. Due to low
species diversity, shortage of water and slow growth rate, the
desert plant communities, if faced with a severe stress take a
long time to recover.
• The Thar Desert in Rajasthan is most typical desert landscape in
india. This has sand dunes. There are also areas covered with
sparse grasses and a few shrubs, which grow if it rains.
• In most areas of the Thar the rainfall is scanty and sporadic. In an
area it may rain only once every few years.
Aquatic ecosystems:
• Ecosystems where water is the dominant environmental factor in controlling
abiotic characteristics and the floral and faunal makeup are known as the aquatic
ecosystems. They include oceans, seas, estuaries, rivers, lakes, ponds, etc.
Abiotic characteristics:
• Some of the important abiotic environmental factors of aquatic ecosystems
include substrate type, water depth, nutrient levels, temperature, salinity, and
flow.
• It is often difficult to determine the relative importance of these factors
without rather large experiments. The amount of dissolved oxygen in a water
body is frequently the key substance in determining the extent and kinds of
organic life in the water body. Fish need dissolved oxygen to survive, although
their tolerance to low oxygen varies among species; in extreme cases of low
oxygen some fish even resort to air gulping.
• Plants often have to produce aerenchyma, while the shape and size of leaves
may also be altered. Conversely, oxygen is fatal to many kinds of anaerobic
bacteria.
• Nutrient levels are important in controlling the abundance of many species of
algae.
• The relative abundance of nitrogen and phosphorus can in effect determine
which species of algae come to dominate.
• Algae are a very important source of food for aquatic life, but at the same time,
if they become over-abundant, they can cause declines in fish when they decay.
• The salinity of the water body is also a determining factor in the kinds of species
found in the water body.
• Organisms in marine ecosystems tolerate salinity, while many freshwater
organisms are intolerant of salt.
• The degree of salinity in an estuary or delta is an important control upon the type
of wetland (fresh, intermediate, or brackish), and the associated animal species.
• Dams built upstream may reduce spring flooding, and reduce sediment
accretion, and may therefore lead to saltwater intrusion in coastal wetlands.
Biotic characteristics:
• The biotic characteristics are mainly determined by the organisms
that occur. For example, wetland plants may produce dense canopies
that cover large areas of sediment—or snails or geese may graze the
vegetation leaving large mud flats.
• Aquatic environments have relatively low oxygen levels, forcing
adaptation by the organisms found there. For example, many
wetland plants must produce aerenchyma to carry oxygen to roots.
• Other biotic characteristics are more subtle and difficult to measure,
such as the relative importance of competition, mutualism or
predation.
• There are a growing number of cases where predation by coastal
herbivores including snails, geese and mammals appears to be a
dominant biotic factor.
Autotrophic organisms:
• Autotrophic organisms are producers that generate organic
compounds from inorganic material.
• Algae use solar energy to generate biomass from carbon dioxide and
are possibly the most important autotrophic organisms in aquatic
environments. In the shallow waters the biomass contribution from
rooted and floating vascular plants is greater.
• These two sources combine to produce the extraordinary production
of estuaries and wetlands, as this autotrophic biomass is converted
into fish, birds, amphibians and other aquatic species.
• Chemosynthetic bacteria are found in benthic marine ecosystems.
These organisms are able to feed on hydrogen sulfide in water that
comes from volcanic vents. Great concentrations of animals that feed
on these bacteria are found around volcanic vents.
Heterotrophic organisms:
• Heterotrophic organisms consume autotrophic organisms and use the
organic compounds in their bodies as energy sources and as raw
materials to create their own biomass.
• Euryhaline organisms are salt tolerant and can survive in marine
ecosystems, while stenohaline or salt intolerant species can only live
in freshwater environments.
• The two main types of aquatic ecosystems are marine ecosystems
and freshwater ecosystems. These major types can further be divided
into many categories depending upon various environmental factors.
 Marine Ecosystem:
• Marine ecosystems cover approximately 71% of the Earth’s surface
and contain approximately 97% of the planet’s water.
• They generate 32% of the world’s net primary production. They are
distinguished from freshwater ecosystems due to the presence of
dissolved compounds, especially salts in the water in high
concentrations.
• Approximately 85% of the dissolved materials in seawater are
sodium and chlorine though the salinity varies among different
marine ecosystems, seawater has an average salinity of 35 parts per
thousand (ppt) of water.
• Various classes of organisms found in marine ecosystems include
brown algae, dinoflagellates, corals, cephalopods, echinoderms, and
sharks. Fishes caught in marine ecosystems are the biggest source of
commercial foods obtained from wild populations.
 Marine ecosystems can be divided into
many zones depending upon water depth
and shoreline features.
 The oceanic zone is the vast open part
of the ocean where animals such as
whales, sharks, and tuna live.
 The benthic zone consists of substrates
below water where many invertebrates
live. The intertidal zone is the area
between high and low tides; in figure it is
termed the littoral zone.
 Other near-shore (neritic) zones can
include estuaries, salt marshes, coral
reefs, lagoons and mangrove swamps.

 In the deep water, hydrothermal vents may occur where chemosynthetic sulfur bacteria form
the base of the food web.
Oceans are the major sinks of carbon dioxide and play an important role in regulating many
biogeochemical cycles and hydrological cycle, thereby regulating the earth’s climate.
• The oceans have two major life zones:
• Coastal zone: this is relatively warm, nutrient rich shallow water. Due to high
nutrients and ample sunlight this is the zone of high primary productivity.
• Open sea: It is the deeper part of the ocean, away from the continental shelf (The
submerged part of the continent). It is vertically divided into three regions:
(i) Euphotic zone which receives abundant light and shows high photosynthetic
activity.
(ii) Bathyal zone receives dim light and is usually geologically active.
(iii) Abyssal zone is the dark zone, 2000 to 5000 metres deep. The abyssal zone has
no primary source of energy i.e. solar energy. It is the world’s largest ecological
unit but it is an incomplete ecosystem.
• Environmental problems concerning marine ecosystems include unsustainable
exploitation of marine resources (for example overfishing of certain species),
marine pollution, climate change, and building on coastal areas
Freshwater Ecosystem
• Freshwater ecosystems cover 0.80% of the Earth’s surface andconsist
0.009% of its total water. They generate nearly 3% of its net primary
production. There are three basic types of freshwater ecosystems:
• Lentic: Standing water, including pools, ponds, and lakes.
• Lotic: Moving water, for example streams and rivers.
• Wetlands: Areas where the soil is saturated or inundated for at least
part of the time.
➢ Lentic Water Ecosystems:

The three primary zones of a lake

Lakes
• Lake ecosystems can be divided into zones. The first, the littoral zone, is the
shallow zone near the shore where rooted wetland plants occur.
• The offshore is divided into two further zones, an open water zone and a
deep water zone.
• In the open water zone (or photic zone) sunlight supports photosynthetic
algae, and the species that feed upon them.
• In the deep water zone(aphotic), sunlight is not available and the food web
is based on detritus entering from the littoral and photic zones. Some
systems use other names.
• The off shore areas may be called the pelagic zone, and the aphotic zone
may be called the profundal zone.
• Towards inland from the littoral zone one can also frequently identify a
riparian zone which has plants still affected by the presence of the lake—this
can include effects from windfalls, spring flooding, and winter ice damage
• The production of the lake as a whole is the result of production from plants
growing in the littoral zone, combined with production from plankton
growing in the open water.
➢ Lakes have several types of organisms:
a) Planktons that float on the surface of waters e.g. phytoplanktons like
algae and zooplanktons like rotifers.
b) Nektons that swim e.g. fishes.
c) Neustons that rest or swim on the surface.
d) Benthos that are attached to bottom sediments e.g. snails.
e) Periphytons that are attached or clinging to other plants or any other
surface e.g. crustaceans.
 Small/ Big/ Great
Fresh water Lake Ecosystem
Average lake Lakes
✓ Stratification:
• This is an important feature of temperate region lakes which show vertical
zonation of its water based on temperature differences.
• During summer, the top waters become warmer than the bottom waters.
Therefore, only the warm top layer circulates without mixing with the
colder layers below. Different layers exhibit different physical, chemical and
biological characteristics.
• Following zones are generally described in lakes which show stratification
or zonation.
i. Epilimnion : Warm, lighter, circulating surface layer
ii. Hypolimnion : Cold, viscous, non-circulating bottom layer.
iii. Thermocline: In between the two -warmer and colder- layers lies the
region of sharp drop in temperature which is known as thermocline.
➢ Types of Lakes:
• Some important types of lakes are:
1. On the basis of nutrient status
a) Oligotrophic lakes which have low nutrient concentrations.
b) Eutrophic lakes which are over nourished by nutrients like nitrogen and
phosphorus, usually as a result of agricultural run-off or municipal sewage
discharge. They are covered with algal blooms. e.g. Dal Lake.
c) Dystrophic lakes that have low pH, high humic acid content and brown
waters e.g. bog lakes.
2. On the basis of origin
d) Volcanic lakes that receive water from magma after volcanic eruptions
e.g. many lakes in Japan. They have highly restricted biota.
e) Artificial lakes or impoundments that are created due to construction of
dams e.g. Govind sagar lake at Bhakra-Nangal, Bagliar lake near Ramban
3. On the basis of salt content
f) Fresh water lakes such as Wular lake in Kashmir
g) Saltwater lakes eg Pangong lake in Leh
h) Meromictic lakes that are rich in salts and are permanently
stratified e.g. lake Nevada.
i) Desert salt lakes that occur in arid regions and have developed
high salt concentrations as a result of high evaporation. e.g.
Sambhar lake in Rajasthan.
Others
j) Endemic lakes that are very ancient, deep and have endemic
fauna which are restricted only to that lake e.g. the Lake Baikal
in Russia; the deepest lake, which is now suffering a threat due
to industrial pollution.
Ponds
• Ponds are small bodies of freshwater with shallow and still water, marsh,
and aquatic plants.
• They can be further divided into four zones: vegetation zone, open water,
bottom mud and surface film.
• The size and depth of ponds often varies greatly with the time of year;
many ponds are produced by spring flooding from rivers.
• Food webs are based both on free-floating algae and upon aquatic plants.
• There is usually a diverse array of aquatic life, with a few examples
including algae, snails, fish, beetles, water bugs, frogs, turtles, otters and
muskrats.
• Top predators may include large fish, herons, or alligators.
• Since fish are a major predator upon amphibian larvae, ponds that dry up
each year, thereby killing resident fish, provide important refugia for
amphibian breeding.
Pond Ecosystem
• Ponds that dry up completely each year are often known as vernal pools.
• Some ponds are produced by animal activity, including alligator holes and
beaver ponds, and these add important diversity to landscapes.
➢ Lotic Water Ecosystems:
• River Ecosystem:
• The major zones in river ecosystems are determined by the river
bed’s gradient or by the velocity of the current.
• Faster moving turbulent water typically contains greater
concentrations of dissolved oxygen, which supports greater
biodiversity than the slow moving water of pools.
• These distinctions form the basis for the division of rivers into upland
and lowland rivers.
• The food base of streams within riparian forests is mostly derived
from the trees, but wider streams and those that lack a canopy derive
the majority of their food base from algae.
• Environmental threats to rivers include loss of water, dams, chemical
pollution and introduced species
River Ecosystem
 Wetland Ecosystems
• Wetlands are dominated by vascular plants that have adapted to saturated soil.
• There are four main types of wetlands: swamp, marsh, fen and bog (both fens and
bogs are types of mire).
• Wetlands are the most productive natural ecosystems in the world because of the
proximity of water and soil.
• Hence they support large numbers of plant and animal species.
• Due to their productivity, wetlands are often converted into dry land with dykes and
drains and used for agricultural purposes.
Wetland Ecosystems
Estuarine ecosystem
• Though a type aquatic ecosystem, an estuary is a transitional zone between
marine and fresh water ecosystems and hence exhibits some unique
characteristics in addition to those common with marine or fresh waters
• Estuaries are places where rivers meet the sea and may be defined as areas
where salt water is measurably diluted with fresh water.
• On average, estuaries are biologically more productive than either the adjacent
river or the sea because they have a special kind of water circulation that traps
plant nutrients and stimulates primary production.
• Fresh water, being lighter than salt water, tends to form a distinct layer that
floats at the surface of the estuary. At the boundary between fresh and salt
water, there is a certain amount of mixing caused by the flow of fresh water over
salt and by the ebb and flow of tides.
• Additional mixing may be caused from time to time by strong winds and by
internal waves that are propagated along the interface between fresh and salt
water.
• Types of estuary are recognized according to the degree of mixing:
• salt wedge estuaries,
• partially mixed estuaries and
• vertically homogeneous estuaries.
• A salt wedge estuary has minimal mixing and the salt water forms a wedge,
thickest at the seaward end, tapering to a very thin layer at the landward limit.
• In a partially mixed estuary, the vigorous rise and fall of the tide generates strong
turbulence and causes partial mixing between the fresh water above and the salt
water below.
• In a vertically homogeneous estuary the river flow is weak and the tidal flow is
strong. Consequently, all stratification is broken down and salinity is almost the
same from top to bottom at any given place. The salinity is lowest where the river
enters the estuary and highest near the sea.
 Increasing salinity

(A) salt wedge estuary, (B) partially mixed estuary, (C) vertically homogeneous estuary, (D) fjord
(black arrows indicate salt water and white arrows fresh).
• The high level of plant production in estuaries supports a
correspondingly high level of production of invertebrate animals and
fish.
• Estuaries often contain beds of shellfish such as mussels and oysters
and large populations of shrimps and crabs.
• Fish such as plaice and flounders are common. Other species use the
estuaries as nursery grounds.
• Organisms in early stages of development enter the salt wedge at the
seaward end and are carried up the estuary by the bottom currents.
Threats:
• Juveniles find abundant food as well as protection
from predators in the mangrove forests, salt marshes,
or sea-grass beds that line the estuary. Later, they may
migrate to the open ocean to continue their growth
and development.
• Other species pass through the estuaries in the course
of their migrations. For example, salmon migrate from
the sea to the rivers to spawn, while the young fish
later migrate back to the sea.
• Eels migrate in the opposite direction, breeding in the
sea but returning to fresh water as juveniles.
Bio geochemical Cycles
• Cycling of materials between the
environment and organisms
• Chemical and biological processes
• Examples Plants obtain nitrogen
• Water cycle from nitrogen-fixing
bacteria and pass it to
• Nitrogen cycle other organisms through
the food chain
• Phosphorus cycle
• Carbon cycle
Water Cycle
Nitrogen Cycle
Carbon Cycle
 Biogeochemical Cycle Activity
• Pass out untitled diagrams of the water cycle, nitrogen cycle, and
carbon cycle.
• Have students title each cycle and explain why they chose these titles.
• Provide a list of labeling terms and have students create labels for
each stage or process on all three diagrams.
• Applications/suggestions
• Use as an introductory or post-discussion assessment.
• Laminate group sets and use erasable markers to save paper and prep time.
• The term “biogeochemical” indicates that in these cycling of nutrients biological,
geological and chemical factors are all involved in the process. The circulation of
chemical nutrients and water takes place through the biological as well as physical
world.
• In effect, the elements are recycled, although in some cycles there may be places
(called reservoirs) where the elements are accumulated or held for a long period
of time (such as an ocean or lake for water).
• The nutrients move through the food chains and ultimately reach the detritus
component (containing dead organic matter) where various microorganisms carry
out the process of decomposition.
• Various organically bound nutrients of dead animal and plants are converted into
inorganic substances by microbial decomposition and are again used up by plants
and the cycles start afresh.
• Some of the important biogeochemical cycles we will discuss briefly here.
 Nitrogen cycle:
• Nitrogen is present in the atmosphere as N2 in large amount
(78%) and it is fixed either by the physical process of lightening or
biologically by some bacteria and/or cyanobacteria (blue green
algae).
• The nitrogen is taken up by plants and used in metabolism for
biosynthesis of amino acids, proteins, vitamins etc. and passes
through the food chain.
• After death of the plants and animals, the organic nitrogen the
organic nitrogen in dead tissues is decomposed by several groups
of ammonifying and nitrifying bacteria which convert them into
ammonia, nitrites and nitrates, which are again used by plants.
• Some bacteria convert nitrates, into molecular nitrogen or N2
which is released back into the atmosphere and the cycle goes
on.
Nitrogen Cycle
Nitrogen Cycle
 Carbon cycle:
• Carbon is taken up by green plants in the form of carbon dioxide as a raw material for
photosynthesis.
• In the process a variety of carbohydrates and other organic substances are produced.
• So it moves through the food chains and ultimately organic carbon present in the dead
matter is returned to the atmosphere as carbon dioxide by microorganisms.
• Respiration by all organisms produces carbon dioxide which is released in the atmosphere
from where is used up by plants.
• In the recent years carbon dioxide levels have increased in the atmosphere due to
burning of fossil fuels etc.
• It has caused an imbalance in the natural cycle and the world today is facing the serious
problem of global warming due to enhanced carbon dioxide emissions in the atmosphere.
Carbon cycle:
 Phosphorus Cycle:
• Reservoir of phosphorus lies in the rocks, fossils etc. which is excavated by man for using it as a
fertilizer.
• Farmers use the phosphate fertilizers indiscriminately and as a result excess phosphates are lost as
run-off, which causes the problem of eutrophication of lakes leading to algal blooms.
• A good proportion of phosphates moving with surface runoff reaches the oceans and lost into the
deep sediments.
• Our limited supply of phosphorus lying in the phosphate rocks of this earth are thus over-exploited
by man and a large part is taken out of the normal cycle due to loss into oceans.
• So human beings are making the phosphorous cycle acyclic.
• Sea birds, on the other hand, are playing an important role in phosphorus cycling. They eat sea-
fishes which are phosphorus rich and the droppings or excreta of the birds return the phosphorus
on the land.
• The Guano deposits on the coasts of Peru are very rich sources of phosphorus.
 Oxygen Cycle:
• Oxygen is taken up by plants and animals from the air during respiration. The
plants return oxygen to the atmosphere during photosynthesis. The main source
of atmospheric free oxygen is photosynthesis, which produces sugars and free
oxygen from carbon dioxide and water:
• Photosynthesizing organisms include the plant life of the land areas as well as the
phytoplankton of the oceans. The tiny marine Cyanobacterium prochlorococcus
accounts for more than half of the photosynthesis of the open ocean.
• An additional source of atmospheric free oxygen comes from photolysis, whereby
high-energy ultraviolet radiation breaks down atmospheric water and nitrous
oxide into component atoms. The free H and N atoms escape into space, leaving
O2 in the atmosphere:

• The main way free oxygen is lost from the atmosphere is via respiration and decay,
mechanisms in which animal life and bacteria consume oxygen and release carbon
dioxide.
• The lithosphere also consumes free oxygen by chemical weathering and surface
reactions. An example of surface weathering chemistry is formation of iron oxides
(rust):
• Oxygen is also cycled between the biosphere and
lithosphere.
• Marine organisms in the biosphere create calcium
carbonate shell material (CaCO3 ) that is rich in oxygen.
• When the organism dies, its shell is deposited on the
shallow sea floor and buried over time to create the
limestone sedimentary rock of the lithosphere.
• Weathering processes initiated by organisms can also free
oxygen from the lithosphere. Plants and animals extract
nutrient minerals from rocks and release oxygen in the
process.
 Hydrological cycle:
• The mass of water on Earth remains fairly constant over time but the partitioning
of the water into the major reservoirs of ice, fresh water, saline water and
atmospheric water is variable depending on a wide range of climatic variables.
• The water moves from one reservoir to another, such as from river to ocean, or
from the ocean to the atmosphere, by the physical processes of evaporation,
condensation, precipitation, infiltration, runoff, and subsurface flow.
• In doing so, the water goes through different phases: liquid, solid (ice), and gas
(vapor).
• The water cycle, also known as the hydrologic cycle, describes the continuous
movement of water on, above and below the surface of the Earth.
• The sun, which drives the water cycle, heats water in oceans and seas. Water
evaporates as water vapour into the air.
• Ice, rain and snow can sublimate directly into water vapour. Evapotranspiration is
water transpired from plants and evaporated from the soil.
• Rising air currents take the vapour up into the atmosphere where cooler
temperatures cause it to condense into clouds.
• Air currents move water vapour around the globe, cloud particles collide, grow,
and fall out of the upper atmospheric layers as precipitation.
• Some precipitation falls as snow or hail, sleet, and can accumulate as ice caps and
glaciers, which can store frozen water for thousands of years.
• Most water falls back into the oceans or onto land as rain, where the water flows
over the ground as surface runoff.
• A portion of runoff enters rivers in valleys in the landscape, with stream flow
moving water towards the oceans.
• Runoff and water emerging from the ground (groundwater) may be stored as
freshwater in lakes. Not all runoff flows into rivers, much of it soaks into the
ground as infiltration.
• Some water infiltrates deep into the ground and replenishes aquifers, which can store
freshwater for long periods of time.
• Some infiltration stays close to the land surface and can seep back into surface water
bodies (and the ocean) as groundwater discharge.
• Some groundwater finds openings in the land surface and comes out as freshwater
springs.
• In river valleys and flood-plains there is often continuous water exchange between
surface water and ground water in the hydrospheric zone. Over time, the water
returns to the ocean, to continue the water cycle.
• The water cycle involves the exchange of energy, which leads to temperature
changes. For instance, when water evaporates, it takes up energy from its
surroundings and cools the environment. When it condenses, it releases energy and
warms the environment. These heat exchanges influence climate
• The evaporative phase of the cycle purifies water which then replenishes the land with
freshwater.
• The flow of liquid water and ice transports minerals across the globe. It is also involved in
reshaping the geological features of the Earth, through processes including erosion and
sedimentation.
• The water cycle is also essential for the maintenance of most life and ecosystems on the planet.
• Biogeochemical cycles are also the links between different components of the environment such
as lithosphere, hydrosphere, atmosphere and biosphere. They portray the movements of
substances on the entire globe.
• Together in a systematic manner these cycles are responsible for maintaining life on earth.
• If man, through his excessive interference, disturbs these cycles beyond the limits that nature
can sustain, they will eventually break down and lead to a degraded earth on which man will not
be able to survive
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