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Earthworms help in breakdown of complex organic matter as well as loosening of the soil. This helps in the proper growth of the crops. Therefore, they are considered farmer’s friend.

• Humification: The process of accumulation of a dark coloured amorphous substance called humus that is highly resistant to microbial action and undergoes decomposition at an extremely slow rate is called humification. 

• Mineralisation: The process by which humus is further degraded by some microbes to release inorganic nutrients is called mineralisation.

Humification leads to accumulation of a dark coloured amorphous substance called humus that is highly resistant to microbial action and undergoes decomposition at an extremely slow rate. Being colloidal in nature it serves as a reservoir of nutrients . The humus is further degraded by some microbes and release of inorganic nutrients occur by the process known as mineralisation.

Oceans contribute about 55 billion tonnes, which is about 32.5%.

Fragmentation, leaching, catabolism, humification and mineralisation.

Pond has biotic and abiotic components 

(a) Biotic – Phytoplankton, Zooplankton, small fishes, large fishes, frogs, snake ,etc. 

(b) Abiotic - water, dissolved organic and inorganic substances, sunlight, temp. Phytoplankton (microscopic plants) – producers. 

Zooplankton (microscopic animals) – primary consumers .Small fishes - secondary consumers. Large fishes, frog, snails – tertiary consumers. 

• A pond is a fairly self sustainable unit that shows even complex interactions of an aquatic ecosystem.
• It is a shallow water body in which all the major/basic components of an ecosystem are well exhibited.

The abiotic components include

• Water with all the dissolved inorganic and organic substances.
• The rich soil deposits at the bottom.
• The solar input.
• The cycle of day length and temperature
• Other elematic factors.

The biotic components include.

• The producers or autotrophic components that include phytoplanktons, some algae, floating, submerged and marginal plants.
• The consumers represented by zooplanktons free swimming animals, bottom dwelting animals etc.

• Fragmentation:- 

It is the process of breaking of the detritus into smaller particles by detrivores like earth worm.

• Leaching:- 

It is the process in which water soluble inorganic substances rundown into soil horizon and get precipitated as salts.

• Catabolism:- 

The enzymatic conversion of the detritus into simple organic compounds and then into inorganic compounds is called catabolism.
The enzymes are secreted by the decomposers like bacteria and fungal.

• Humification:- 

Humification during decomposition leads to the accumulation of a dark coloured amorphous substance called, humus.

• Mineralisation:-

It is the process in which the humus is degraded by certain micro organisms and the inorganic nutrients are released.

• If the detritus is rich in lignin and chitin the decomposition is slow.
• If the detritus rich in nitrogen and water soluble substances like sugars, decomposition is faster.

CO₂ is added to the atmosphere in the following ways:

• Burning of fossil fuels
• Volcanic activity
• Forest fire
• Respiratory activities

The pyramid of energy is always upright because there is a gradual decrease in the energy contents in successive trophic levels from producers to consumers of various order. According to Linderman's 10% law only 10% of the total energy is available to the next higher trophic level.

The pioneer species on a bare rock are usually lichen, mosses and annual grass stage, and blue-green algae. In primary succession rocks, lichens are able to secrete acids to dissolve rocks, helping in weathering and soil formation. It paves way to some very small plants like bryophytes, which are able to take hold in the small amount of soil. They are, with time, succeeded by bigger plants. 

Several hard and light demanding trees grow in the area occupied by shrubs. Slowly environment becomes more moist and shadier so that plants of climax community can spread in this area. The type of climax community that will ultimately get established are shrubs and trees.

The pyramid of energy represents the total amount of energy consumed by each trophic level in a given food chain. 

The total amount of energy available for utilization in the layers above is less than the energy available in the lower levels. This happens because according to 10% law of energy transfer, only 10% of the total energy is transferred from one trophic level to another.

Gradual/predictable change in the species composition of given area. Rate of succession would be faster in a forest destroyed by a forest fire. Such disturbances create new conditions that encourage some species and discourage or eliminate other species/ since after a forest fire some soil is already Present. So, succession is faster than primary succession.

The components of lake ecosystem (viz : abiotic components, biotic components, consumers of various order and decomposers) function as an unit for various function of ecosystem as follows:

(i) Productivity - conversion of inorganic into organic material with the help of solar energy by the autotrophs.

(ii) Energy flow - unidirectional movement of energy towards higher trophic level (and its dissipation and loss as heat to the environment)

(iii) Decomposition - fragmentation, leaching, catabolism, humification, mineralization by bacteria, fungi and flagellates (abundant at the bottom of lake)

(iv) Nutrient cycling - decomposition of dead matter to release the nutrients back to be re-used by the autotrophs.

Food chain in aquatic ecosystem (lake)

Phytoplanktons => Zooplanktons => Small fish => Big fish

Xerarch Succession : 

• Takes place in dry area hence progress from xeric to mesic condition
• Pioneer species such as lichens secrete acids to break rocks, initiate soil formation
• Lichens pave way to bryophytes
• Which are succeeded by bigger plants. Ultimately, stable mesic community is formed.

It is because the productivity available to the consumer of next trophic level for consumption is the resultant of the primary productivity from plants.

The decomposers are the microorganisms that can feed or operate at any of the trophic level in ecosystem. They decompose the organic matter of both the autotrophs as well as the heterotrophs. Therefore they are not given any fixed trophic level in an ecosystem.

Many organisms occupy different positions in different food chains, several food chains get interconnected to form the food web.

Green Plants are producers. They capture radiant energy of the sun during photosynthesis All other organisms depend upon plants directly (herbivores) or indirectly (carnivores) for their energy requirement. Thus the energy flows from producers to a number of consumers of various order in a unidirectional manner and it is neither created nor destroyed. In this way the first law of thermodynamics is satisfied in ecosystem functioning.

A snake eating a mouse in a field/lawn occupies the third trophic level in the food chain.
Plants → Mice → Snake

When the snake eats frog in the same field, it occupies the 4th trophic level in a food chain it is because the frog feeds on some of the insects which depends on the plants.

Plants → Insects → Frog → Snake

Thus in the same ecosystem one animal (snake) occupies more than one trophic level at the same time as it cannot satisfy its food need from one trophic level.

Secondary productivity indicates the organic matter synthesized by the consumers specially by the primary consumers or herbivores. The two factors by which the productivity is limited in an aquatic ecosystem are Iight and nutrient supply.

Gross productivity - Rate of production of organic matter during photosynthesis. 

Net primary productivity - Available biomass for the consumption to heterotrophs.

GPP - R = NPP.

NPP = GPP - R 

Productivity is the rate of production of biomass at any trophic level at any given interval of time. 

Gross productivity : It is the rate of production of organic matter by green plants per unit time per unit area. On the other hand we can say that total amount of productivity. 

Net Primary Productivity : It is the different between gross primary productivity and the loss due to respiration. 

Secondary Productivity : It is rate of production or formation of new organic matter by consumers especially the consumers of the first order or herbivores. 

For example, sparrow is an omnivore. When it eats seeds, fruits or any other plant product, it occupies the primary trophic level. Whereas, when it eats worms and any other insect, it occupies the secondary trophic level. Thus, it occupies more than one trophic level in the same ecosystem.

NPP = GPP - R 

NPP = Net Primary Productivity. 

GPP = Gross Primary Productivity. 

R = Respiration losses.

Productivity is the rate of biomass production.

GPP – R = NPP = 1

Where NPP is biomass available to consumers for secondary productivity.

GPP  –  R  =  NPP

Gross productivity (GPP) is the rate of production of organic matter during photosynthesis. Net primary productivity (NPP) is the available biomass for the consumption by heterotrophs.

GPP − R = NPP

Alternative path of energy flow are found in Food web.