The fresh water and Ecosystem:-

Pond is a self-sustained ecosystem present in a shallow water body. It has all the structural componenets which work as a unit and show all the four functional aspects of the ecosystem.

Structure:- It has both abiotic and biotic componenets.

Abiotic components include water, dissolved inorqanic and organic substances and soil deposit at the bottom. Solar energy cycle of temperature, day length and other climatic conditions regulate the functions.

Biotic component are producers, consumers and decomposers. Producers are autotrops like phytoplankton, some large algae, submerged floating and amphibious (towards the edge) plants. Consumers are zooplankton, free swimming and bottom dwelling animals. They are differentiate into herbivores and carnivores. The important herbivores are zooplankton, larvae, tadpole and some fish. Primary carnivores include water scorpions, water Beetle, dragonfly larvae, Hydra and some fish secondary carnivores are large fish and many water birds. Decomposers include fungi bacteria and flagellates. They are especially abundant at the bottom.

Functions:- A pond peforms the functions of any ecosystem as well as the biosphere as a whole. With the help of radiant energy, autotrophs convert the inorganic materials into organic matter. It is primary productivity. Autotrophs are consumed by heterotrophs which build up their own organic matter. It is secondary productivity. Organic wastes and dead organisms are acted upon by decomposers. Minerals are realeased is the process. The minerals become available to autotrophs for reuse.

There is cycling and recycling of matter. However, energy flow is undirectional. Solar energy is trapped by autotrophs. A part of it is lost by autotrophs. As organic matter, energy  passes to consumers. Every category of consumer dissipates a part of energy. The dissipated energy is lost as heat to the environment.