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Wetlands - Types Of Wetlands

wildlife isolated water estuarine

A wide variety of wetlands exist across the United States because of regional and local differences in hydrology, water chemistry, vegetation, soils, topography, and other factors. There are two large groups of wetlands: estuarine (coastal) and palustrine (inland). Estuarine wetlands are linked to estuaries and oceans and comprise 5% of the wetlands in the forty-eight contiguous states. Estuaries are places where fresh and salt water mix, such as a bay or where a river enters the ocean. In estuaries, the environment is one of ever-changing salinity and temperature. The water level fluctuates in response to wind and tide. Examples of estuarine wetlands are saltwater marshes and mangrove swamps.

Palustrine wetlands comprise the other 95% of wetlands. The most common location of palustrine wetlands is the floodplains of rivers and streams, the margins of lakes and ponds, and isolated depressions surrounded by dry land. Some examples of inland wetlands are the Florida Everglades, wet meadows, swamps, fens, bogs, prairie potholes, playa lakes, and wet tundra.

Wetlands are further divided by their vegetation. Emergent wetlands (marshes and wet meadows) are dominated by grasses, sedges, and other herbaceous (non-woody) plants. Emergent wetlands account for 74% of estuarine wetlands, while representing only 25% of palustrine wetlands. Shrub wetlands (including shrub swamps and bogs), characterized by low-to-medium-height woody plants, make up 13% of estuarine wetlands and account for 18% of freshwater wetlands. Forested wetlands, mostly wooded swamps and bottomland hard-wood forests, are dominated by trees and account for 51% of freshwater wetlands.

The U.S. Fish and Wildlife Service (USFWS) is the agency charged with conducting wetland status and trend studies of the nation's wetlands at ten-year intervals. To accurately report wetland status, the USFWS has further subdivided estuarine and palustrine wetlands into numerous habitat categories.

Geographically isolated wetlands are another type of important wetland in the United States. The U.S. Fish and Wildlife Service defines them as "wetlands with no apparent surface water connection to perennial rivers and streams, estuaries, or the ocean." They have no surface water outlet and therefore are vulnerable to changes in surrounding land use practices. Steve Williams, director of the U.S. Fish and Wildlife Service, said in a June 11, 2002, news release, "In desert areas, isolated wetlands provide vital fresh water oases for wildlife and function as stepping stones for migrating birds. Their isolation has promoted the evolution of unique plant and animal life that is specially adapted to these habitats." Williams also pointed out that isolated wetlands are important to human beings because many of the wetlands contribute important subsurface water flows to other wetlands and streams. In areas such as the Prairie Pothole Region, isolated wetlands store rainwater, which reduces flooding and recharges groundwater supplies, in addition to providing habitat for wildlife. On June 11, 2002, the U.S. Fish and Wildlife Service released a report (Geographically Isolated Wetlands: A Preliminary Assessment of Their Characteristics and Status in Selected Areas of the United States) that describes nineteen types of isolated wetlands in seventy-two study areas and provides ecological profiles of their fish and wildlife conservation values.

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