DEFINITION
Wetlands are areas where water covers the soil, or is present either at or near the surface of the soil all year or for varying periods of time during the year, including during the growing season. Water saturation (hydrology) largely determines how the soil develops and the types of plant and animal communities living in and on the soil. Wetlands may support both aquatic and terrestrial species. The prolonged presence of water creates conditions that favor the growth of specially adapted plants (hydrophytes) and promote the development of characteristic wetland (hydric) soils.

Wetlands vary widely because of regional and local differences in soils, topography, climate, hydrology, water chemistry, vegetation, and other factors, including human disturbance. Indeed, wetlands are found from the tundra to the tropics and on every continent except Antarctica. Two general categories of wetlands are recognized: coastal or tidal wetlands and inland or non-tidal wetlands.

Many of these wetlands are seasonal (they are dry one or more seasons every year), and, particularly in the arid and semiarid West, may be wet only periodically. The quantity of water present and the timing of its presence in part determine the functions of a wetland and its role in the environment
(www.epa.gov)

AKA
Wetlands have been categorized both as biomes and ecosystems. Wetlands include Swamps, Marches, Bogs, Flooded grasslands and savannas, Ripiarian zones an Sloughs.

PERFORMANCE CRITERIA
Wetlands (either natural or man-made) have five primary functions:

1) Water quality improvement - Plants (especially their root systems) slow the flow the water, allowing sediment to 'drop' out. Micro-organisms absorb excess nutrients. In some states, man-made wetlands are constructed in some small scale wastewater treatment plants. They serve to 'polish' (e.g. nutrient or sediment removal) the effluent in the final stage of the treatment process.

2) Floodwater storage - Wetlands are nature's way of providing storing excess flood waters. According to the USGS, At the time of European settlement in the early 1600's, the area that was to become the conterminous United States had approximately 221 million acres of wetlands. About 103 million acres remained as of the mid-1980's (Dahl and Johnson, 1991). ... By the 1960's, most political, financial, and institutional incentives to drain or destroy wetlands were in place. The Federal Government encouraged land drainage and wetland destruction through a variety of legislative and policy instruments. For example, the Watershed Protection and Flood Prevention Act (1954) directly and indirectly increased the drainage of wetlands near flood-control projects (Erickson and others, 1979). The Federal Government directly subsidized or facilitated wetland losses through its many public-works projects, technical practices, and cost-shared drainage programs administered by the U.S. Department of Agriculture (Erickson, 1979). Tile and open-ditch drainage were considered conservation practices under the Agriculture Conservation Program--whose policies caused wetland losses averaging 550,000 acres each year from the mid-1950's to the mid-1970's ... The effects of the Federal policy reversal on the rate of wetland loss are not clear. Estimates indicate that wetland losses in the conterminous United States from the mid-1970's to the mid-1980's were about 290,000 acres per year (Dahl and Johnson, 1991). This is about one-half of the losses that occurred each year in the 1950's and '60's. The preceding numbers do not include degraded or modified wetlands. Although the estimate above reflects a declining rate of loss, land development continues to destroy wetlands. From about 1987 to the present, Federal efforts to restore wetlands have increased. Although there is no precise number for all of the wetland acres restored, the U.S. Fish and Wildlife Service (1991) estimated that between 1987 and 1990 about 90,000 acres were added to the Nation's wetland inventory.(Source: Dahl, Thomas E. and Allord, Gregory J.Technical Aspects of Wetlands: History of Wetlands in the Counterminous United States)

3) Fish & wildlife habitat -According bto the US`EPA, 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. Many other animals and plants depend on wetlands for survival. Estuarine and marine fish and shellfish, various birds, and certain mammals must have coastal wetlands to survive. Most commercial and game fish breed and raise their young in coastal marshes and estuaries. Menhaden, flounder, sea trout, spot, croaker, and striped bass are among the more familiar fish that depend on coastal wetlands. Shrimp, oysters, clams, and blue and Dungeness crabs likewise need these wetlands for food, shelter, and breeding grounds. For many animals and plants, like wood ducks, muskrat, cattails, and swamp rose, inland wetlands are the only places they can live. Beaver may actually create their own wetlands. 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 coastal and inland wetlands as resting, feeding, breeding, or nesting grounds for at least part of the year. Indeed, an international agreement to protect wetlands of international importance was developed because some species of migratory birds are completely dependent on certain wetlands and would become extinct if those wetlands were destroyed.

4) Aesthetics - According to the US EPA, Wetlands have recreational, historical, scientific, and cultural values. More than half of all U.S. adults (98 million) hunt, fish, birdwatch or photograph wildlife. They spend a total of $59.5 billion annually. Painters and writers continue to capture the beauty of wetlands on canvas and paper, or through cameras, and video and sound recorders. Others appreciate these wonderlands through hiking, boating, and other recreational activities. Almost everyone likes being on or near the water; part of the enjoyment is the varied, fascinating lifeforms; and

5) Biological productivity - According to Earthplatform.com, Wetlands are some of the most biologically productive natural ecosystems in the world, and are comparable in their productivity and diversity of species, to tropical rain forests and coral reefs. Abundant vegetation and shallow water provide diverse habitats for fish and wildlife. Aquatic plant life flourishes in the nutrient-rich environment, and energy converted by the plants, is passed up the food chain to fish, waterfowl, and other wildlife and to people as well. In this way, the wetlands are supporting valuable commercial fish and shellfish industries.

ILLUSTRATION





CASE STUDIES
Waterworks Gardens, Renton
Meadowbrook Pond, Seattle
Tezozomoc Park, Mexico City
Xochimilco Ecological Park, Mexico City

ADDITIONAL RESOURCES

US EPA

US Global Change Research Program's statement of some of the ways that wetlands sequester carbon
Lal, R., "Soil Carbon Sequestration Impacts on Global Climate Change and Food Security," Science304: 1623-7 (2004)

Amthor, J.S., Dale, V.H., Edwards, M.T. et al., "Terrestrial Ecosystem Responses to Global Change: A Research Strategy," ORNL Technical Memorandum, 1998/27, Oak Ridge National Laboratory, Oak Ridge Tennessee (1998)

Wetlands, The Encyclopedia of the earth