In physical geography, a wetland is an environment "at the interface between truly terrestrialecosystems...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.
By absorbing the force of strong winds and tides, wetlands protect terrestrial areas adjoining them from storms, floods, and tidal damage. Fresh water marshes are often on riverfloodplains.
A temperate wetland in Britain, with shallow open water and reedbeds.
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.
In waterlogged conditions, decay processes occur relatively slowly, and therefore many wetlands are characterised by thick deposits of sediment.
These sediments consist of the remains of plants, animals and micro-organisms living in and around the wetland, along with other materials brought in by run-off, floods and streams, carried by wind and rain, or left by animals and people, intentionally or accidentally (a lost shoe or fishhook, the remains of a path or platform...).
WAERC is a highly interdisciplinary regional, national and international centre of research, on the record of past landscapes contained within wetland sedimentary systems, both in using archive to reconstruct past environments, and in advising and studying the threat to and preservation of this often vulnerable resource.
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