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In physical geography, a wetland is an environment "at the interface between truly terrestrial ecosystems...and truly aquatic systems...making them different from each yet highly dependent on both" (Mitsch & Gosselink, 1986). In essence, wetlands are ecotones. Wetlands are found under a wide range of hydrological conditions, but at least some of the time water saturates the soil. The result is a hydric soil , one characterized by an absence of free oxygen some or all of the time, and therefore called a "reducing environment." Plants (called hydrophytes or just wetland plants) specifically adapted to the reducing conditions presented by such soils can survive in wetlands, whereas species (called "upland" plants) intolerant of the absence of soil oxygen can not survive. Adaptations to low soil oxygen characterize many wetland species.
- bog or moor or muskeg (peatlands)
- mangrove swamp or mangal
- marsh or fen
- bayou or slough
- constructed wetland
Wetlands are often filled in to be used for everything from agriculture to parking lots, in part because the economic value of wetlands has only been recognised recently: the shrimp and fish that breed in salt water marshes are generally harvested in deeper water, for example. Wetlands support a wide variety of wildlife (bird, plants, fish, mammals etc) and therefore the conservation of wetlands is of prime importance for the preservation of many species of wildlife. In 1962, the idea of wetlands conservation was born with a "List of Wetlands of International Importance". This was followed up in 1971 by the Ramsar Convention when conservationists from 23 countries met in the city of Ramsar, Iran on the shores of the Caspian Sea. There are now over 1,200 wetlands on the Ramsar List.
- Convention on Wetlands of International Importance Especially As Waterfowl Habitat
- Wetlands International
- Wildfowl and Wetlands Trust
- Mitsch, William J., and James G. Gosselink, (1986). Wetlands, New York: Van Nostrand Reinhold, 1986, p. 539.
- Campbell, Craig S., and Michael Ogden, (1999), "Constructed Wetlands In The Sustainable Landscape", New York: John Wiley & Sons, Inc., 1999, p.270.
- United States Geological Survey Water Supply Paper 2425: History of Wetlands in the Conterminous United States
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