Wetlands are ecotones, or transitional areas, commonly located between open water bodies and uplands. This means that the boundaries surrounding a wetland are either predominantly aquatic or mostly dry. Because they are intermediate areas, ecotones often contain more plants and animals than the adjacent habitat found along their edges. Wetlands can be found in each State in the United States.
In general, there are two broad categories of wetlands:
In the United States, coastal wetlands fringe the shoreline along the Atlantic, Pacific, Great Lakes, and Gulf coasts. Each coastal system includes the wetlands immediately along the ocean and those lining the rivers and bays that drain seaward. Fresh river water, runoff, and rain flow down toward the ocean, while sea water, pulsed by the tides, flows inland. This mixed zone of fresh and saline waters forms an estuary. Toward the dry uplands, freshwater marshes and freshwater forested wetlands occur. Salt marshes are generally found near the edge along the ocean.
Inland wetlands exist throughout the Nation's interior. They can usually be found along rivers and streams, in depressions surrounded by dry land, and along the edges of lakes and ponds. Inland wetlands include marshes, wet meadows, shrub swamps, or wooded swamps. Some wetlands are regional, such as the pocosins of North Carolina or the bogs and fens of the northeastern and north-central States and Alaska. Other types of inland wetlands include saline and alkaline marshes, riparian wetlands, prairie potholes, vernal pools, playa lakes, cypress-gum swamps, wet tundra, and tropical rain forests.
While there are many types of wetlands, all wetlands share three common characteristics.
Wetlands such as swamps and marshes are easily recognized, but some wetlands are harder to identify because they are dry during part of the year or don't look very wet from a distance. These include bottomland forests, pocosins, pine savannahs, bogs, wet meadows, potholes, and wet tundra.
In the past, wetlands were considered wastelands—sources of mosquitoes, flies, and unpleasant odors. As a result, more than half of America's original wetlands were destroyed. They were drained and converted to farmland, filled for residential and commercial use, and converted to landfills.
Through research, scientists now know that wetlands are valuable natural resources that provide many important benefits to people and wildlife. Wetlands improve water quality, reduce flood and storm damage, provide important habitat for fish and wildlife, and support recreational activities.