Wetlands: An Introduction
Wetlands are part of the foundation of our nation's water resources and are vital to the health of waterways and communities that are downstream. Wetlands feed downstream waters, trap floodwaters, recharge groundwater supplies, remove pollution, and provide fish and wildlife habitat. Wetlands are also economic drivers because of their key role in fishing, hunting, agriculture and recreation.On this page:
Wetlands are the transitional zones between land and water. They are unique ecosystems where the plants, soil and animals are shaped by the presence of water at or below the surface for at least part of the year. Wetlands include swamps, marshes, bogs and fens. Wetlands vary widely because of differences in soils, topography, climate, hydrology, water chemistry, vegetation, and other factors.
See: detailed descriptions of the different types of wetlands.
Wetlands are found throughout the United States. They are often found alongside waterways and in flood plains. However, wetlands are found all throughout the landscape. Some, like prairie potholes, form in depressions on the land or over poorly drained soils. While some wetlands have no apparent connection to surface water like rivers, lakes or the ocean, most wetlands have critical groundwater connections.
Unique wetlands that don’t have surface water connections are commonly found in the upper Great Lakes, north-central interior and Great Plains regions, but almost every part of the U.S. has such wetlands.
Wetlands perform a wide variety of functions and are important for both the environment and the economy.
See: detailed descriptions of the functions of wetlands.
Wetlands play a key role in recharging groundwater. Even wetlands without an obvious surface water connection store water and may slowly release it into groundwater, aquifers and surface waters. The storage capacity of wetlands can be enormous. For example, in South Carolin, wetlands without a surface connection to downstream waters- like pocosins and hardwood swamps- are estimated to store 45.8 billion gallons of water, or enough to fill about 70,000 Olympic-size swimming pools.1
Flood and erosion protection:
Wetlands function as natural sponges that trap and slowly release surface water, rain, snowmelt, groundwater and flood waters. Trees, roots and other wetland vegetation also slow the flow of flood waters and distribute the excess water more slowly over the floodplain. This lowers flood heights and reduces erosion. Over the last 30 years, freshwater flooding has cost an average of $7.8 billion in direct damage to property and crops each year.2
Wetlands near urban areas are particularly valuable, counteracting the rate and volume of water runoff caused by pavement and buildings. In rural areas, the holding capacity of wetlands helps control floods and prevents water logging of crops.
Some states are restoring wetlands in coastal areas to buffer the storm surges from hurricanes and tropical storms. Wetlands at the margins of lakes, rivers, bays, and the ocean protect shorelines and stream banks against erosion. Wetland plants hold the soil in place with their roots, absorb the energy of waves and break up the flow of stream or river currents.
See: more information about coastal wetlands.
Wetlands are excellent at filtering pollution including nutrients and sediments that can clog waterways. Wetlands are particularly effective at removing nutrient pollution. In studies, a bog in Massachusetts trapped nearly 80% of nitrogen inputs and prairie pothole wetlands in the upper Midwest removed over 80% of the nitrate load. Because of this filtering ability, wetlands prevent expensive treatment downstream.
More than one-third of the United States' threatened and endangered species live only in wetlands, and nearly half use wetlands at some point in their lives.3 For many animals and plants- like wood ducks, muskrat, cattails, and swamp rose- inland wetlands are the only places they can live. For others- such as striped bass, peregrine falcon, otter, black bear, raccoon, and deer- wetlands provide important food, water, or shelter. Many of the U.S. breeding bird populations- including ducks, geese, woodpeckers, hawks, wading birds, and many song-birds- feed, nest, and raise their young in wetlands. Migratory waterfowl use wetlands as resting, feeding, breeding, or nesting grounds for at least part of the year.
Wetlands are important for the economy, particularly for their key role in fishing, hunting, agriculture and recreation. A wealth of natural products come from wetlands, including fish and shellfish, blueberries, cranberries, timber, and wild rice, as well as medicines from wetland soils and plants. Many of the nation's fishing industries harvest wetland-dependent species.
- Fishing:About 40 million anglers spend $45 billion annually on trips, equipment, licenses, and other items to support their fishing activities. The commercial salmon fishery, worth an estimated $555 million in 2010, depends on small streams- and streams that do not flow year round- which serve as spawning areas for salmon as far as 900 miles inland.4
- Hunting:About 2.3 million people per year hunt migratory birds, which depend on healthy wetlands, spending more than $1.3 billion dollars per year in the process.5
See: more information about how wetlands support fishing and hunting.
- Agriculture:Farmers depend on clean water to irrigate farm crops across the country. Irrigation accounts for 37 percent of all surface freshwater withdrawals in the U.S.6