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A pond is an example of a complete, closed and an independent ecosystem. It is convenient to study its basic structure and functions. It works on solar energy and maintains its biotic community in equilibrium. If you collect a glass full of pond water or a scoop full of pond bottom mud, it consists of a mixture of plants, animals, inorganic and organic materials. Following components are found in a pond ecosystem.
(A) Abiotic components
- Light: Solar radiation provides energy that controls the entire system. Penetration of light depends on the transparency of water, amount of dissolved or suspended particles in water and the number of plankton. On the basis of extent of penetration of light a pond can be divided into euphotic (eu=true,photic=light), mesophotic and aphotic zones. Plenty of light is available to plants and animals in the euphotic zone. No light is available in the aphotic zone.
- Inorganic substances: These are water, carbon, nitrogen, phosphorus, calcium and a few other elements like sulphur depending on the location of the pond. The inorganic substances like O2 and CO2 are in the dissolved state in water. All plants and animals depend on water for their food and exchange of gases- nitrogen, phosphorus, sulphur and other inorganic salts are held in reserve in bottom sediment and inside the living organisms. A very small fraction may be in the dissolved state.
- Organic compounds: The commonly found organic matter in the pond are amino acids and humic acids and the breakdown products of dead animals and plants. They are partly dissolved in water and partly suspended in water.
(B) Biotic components
- Producers or autotrophs: synthesize food for all the heterotrophs of the pond. They can be categorized into two groups:-
(a) Floating microorganisms and plants
(b) Rooted plants
(a) Floating microorganisms (green) and plants are called phytoplankton (“phyto”- plants, “plankton” –floating). They are microscopic organisms. Sometimes they are so abundant in the pond that they make it look green in colour e.g. Spirogyra, Ulothrix, Cladophora, Diatoms, Volvox.
(b) Rooted plants: These are arranged in concentric zones from the periphery to the deeper layers. Three distinct zones of aquatic plants can be seen with increasing depth of water in the following order: i) Zone of emergent vegetation:. eg. Typha, Bulrushes and Sagittaria
ii) Zone of rooted vegetation with floating leaves. eg. Nymphaea
iii) Zone of submergent vegetation: eg. All pond weeds like Hydrilla, Rupia,
musk grass etc.
- Consumers/Heterotrophs are animals which feed directly or indirectly on autotrophs eg. Tadpole, snails, sunfish, bass etc.
Pond animals can be classified into the following groups:
(a) Zooplanktons are floating animals. Cyclops, Cypris
(b) Nektons are the animals that can swim and navigate at will. Eg. fishes
(c) Benthic animals are the bottom dwellers: beetle, mites, molluscs and
- Decomposers: They are distributed through out the entire in the whole pond but in the sediment most abundant. There are bacteria and fungi. (Rhizopus, Penicillium, Curvularia , Cladosporium) found at the bottom of the pond.