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
other names, related ideas, etc.

PERFORMANCE CRITERIA
how is it measured? what are the criteria for its design or planning?

ILLUSTRATION
a diagram or drawing that demonstrates the basic pattern or concept

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

ADDITIONAL RESOURCES
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)