A lake is a self sustained aquatic ecosystem with both biotic and abiotic components. Biotic components includes producers, consumers and decomposers. Abiotic components include water, dissolved inorganic and organic substances and soil deposit at the bottom. Solar energy, cycle of temperature, day length and other climatic conditions regulate its functions.

 

Four important functional aspects of the ecosystem are : (i) productivity, (ii) decomposition, (iii) energy flow and (iv) nutrient cycling. A lake performs the functions of any ecosystem as well as the biosphere as a whole.

 

(i) Productivity : The rate of synthesis of energy containing organic matter or biomass by any trophic level per unit area in unit time is described as its productivity. With the help of solar energy, producers (autotrophs) like phytoplanktons, some larger algae, submerged, floating and amphibious plants convert the inorganic materials into organic matter. It is primary productivity. Autotrophs are consumed by heterotrophs like zooplanktons, free swimming and bottom dwelling animals which build up their own organic matter. It is a secondary productivity.

 

(ii) Decomposition : It completely disposes off the whole detritus, i.e., synthesis of organic matter by consumers. Organic wastes and dead organisms are acted upon by decomposers like fungi, bacteria and flagellates. These are especially abundant at the bottom. Minerals are released in the process. The minerals become available to autotrophs for reuse. There is cycling and recycling of matter.

 

(iii) Energy flow : Ecosystem require a constant input of energy as every component of an ecosystem is regularly dissipating energy. Energy flow is unidirectional. Solar energy is trapped by autotroph in a lake and a part of it is lost by autotroph itself. As organic matter, energy passes to consumers, there is decrease in the content and flow of energy with the rise in trophic level as every category of consumer dissipates a part of energy. The dissipated energy is lost as heat to the environment.

 

(iv) Nutrient cycling : It is exchange/circulation of biogenetic nutrients between living and non-living components of biosphere. Essential elements required by organisms for their body building and metabolism which are provided by ecosystem and return to it after death and decay of organisms. Decomposition of dead planktons algae, aquaticplantsandanimalsbydecomposershelps in recycling of biogeochemicals and creating space for newer generations of organisms in a lake.

 

Food chain in a lake ecosystem is as follows : Phytoplankton ï‚® Zooplankton ï‚® Small crustaceans ï‚® Predator insects ï‚® Small fish ï‚® Big fish