Wetlands are now recognized as ecosystems that perform many ecological functions and provide a variety of valuable goods and services. Among them, different wetlands help in groundwater recharge or flood abatement, provide habitats to a large diversity of organisms representing all groups from microorganisms to mammals, enhance the esthetics of the landscape, and above all perform several important biogeo-chemical functions for which they are known as the kidneys of the Earth and also as the agents of climate change (methane emission). Wetlands, other than the bogs, are highly productive systems, with their productivity being generally greater than in adjacent terrestrial systems under similar climatic conditions. Several wetland plants such as Phragmites australis, Arundo donax, Cyperus papyrus, and Eichhornia crassipes often attain a standing crop of more than 10 000gm~ , whereas the net annual production ranges from 1.5 to 2.0 times more than the standing crops. Floodplains and littoral marshes are important grazing lands for many large herbivores including domestic cattle and water buffaloes. Wetlands support very high biodiversity, disproportionate to their area on a global scale. The inland wetlands are estimated to account for about 15% of the Earth's total biodiversity, and may include up to 30% of the total biodiversity of some countries. A significantly large proportion of animal species (particularly insects, amphibians, and reptiles) depends upon the wetlands at some stage of their life cycle, and thousands of animals, especially the waterfowl, annually migrate between wetlands in different continents. Also, a fairly large proportion of wetland fauna are rare, endangered, or threatened. In recognition of their importance for biodiversity, and especially as habitats for the waterfowl, wetlands are the only ecosystem which became the subject of an international convention, the Ramsar Convention, as early as 1971.
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