Wetlands are among the world’s richest and most productive ecosystems. They include swamps, marshes, mangroves, lakes and rivers and cover over 2 million square miles (5.7 million sq km).
Wetlands occur on poorly drained land, where organic matter decays very slowly and peat accumulates, creating bogs. At northern latitudes mosses such as Sphagnum dominate the flora. Where the soil has more nutrients, both inland and at the mouths of great rivers such as the Mississippi and the Nile, grass grows to form marshes. Mangroves, adapted to grow in muddy tidal water that alternates between salty seawater and fresh, occur around deltas and elsewhere. They are mainly found in the tropics, but where ocean currents are favorable, occur also on sub-tropical coasts.
Salt marshes support a large number of invertebrates, providing food for diverse species of birds. Mangrove forests support lichens, orchids, and bacteria, and provide nesting sites for birds, and vital nursery and feeding sites for fish, crustaceans and other shellfish.
Agriculture is the principal cause of wetland destruction, but the damming of rivers can also disrupt these delicate ecosystems. Many wetlands have also been drained in an attempt to destroy the breeding sites of mosquitoes, and thereby control malaria. Wetlands have already been lost in Europe and North America and losses are now high in Asia and Africa. Inter-tidal salt marshes have been “reclaimed” and mangroves destroyed for the development of ports, marinas, housing and commercial fisheries. But salt marshes and mangroves provide vital ecological functions, helping to stabilize estuary banks and provide a barrier against the sea. Their destruction causes erosion and land subsidence and permits salt water to penetrate coastal soils and threaten fresh water supplies.
The Convention on Wetlands was signed in Ramsar, Iran in 1971. By mid-2008, 1,752 sites were included in the Ramsar List of Wetlands of International Importance, representing over 618,000 square miles (1.6 million sq km) of wetlands, nearly twice that in 2001. Signatories to the Convention undertake to practice “wise use” of those wetlands, to sustain their biodiversity.
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