What are Wetlands?

Wetlands are transitional zones between terrestrial and aquatic ecosystems. They are lands that are water-saturated at or near the surface or lands that are covered with shallow water for at least some part of the year. Ranging from the tropics to the subarctic, wetlands are found on every continent except Antarctica (Mitsch & Gosselink 1993 ). Wetlands vary greatly due to regional and local differences in climate, topography, hydrology, vegetation, water chemistry, and soils, so defining them is difficult. Under the Clean Water Act, the term "wetlands" means:

those areas that are inundated or saturated by surface or ground water at a frequency and duration sufficientto support, and that under normal circumstances do support, a prevalence of vegetation typically adapted for lifein saturated soil conditions. Wetlands generally include swamps, marshes, bogs and similar areas.

Wetlands are defined -- or delineated -- according to three criteria

hydrophytic vegetation: water-tolerant plants that have adapted to wetland conditions
hydric soils: water-saturated soils that have become oxygen deficient
hydrologic regime: dominated by the presence of water through flooding or saturated ground

Wetlands are categorized into five major systems

COASTAL WETLANDS

MARINE: open ocean overlying the continental shelf

ESTUARINE: deepwater tidal habitats and adjacent tidal wetlands, brackish water (containing some mix of salt and fresh water)

INLAND WETLANDS

RIVERINE: wetland and deepwater habitats contained within a channel; associated with rivers and streams;

LACUSTRINE: wetlands and deepwater habitats associated with lakes (total area exceeds 20 acres in most cases)

PALUSTRINE: small,shallow ponds; (total area is less than 20 acres); all nontidal wetlands dominated by trees, shrubs, persistent emergents, peatlands

These five systems are further subdivided into "ecological taxa" consisting of subsystems, classes, dominance types, and modifiers. For an in-depth inventory of wetland ecosystems, you can refer to the U.S. Fish and Wildlife Service's hierarchical wetland classification system.

Interested in learning more about wetlands? Check out this site.

This page was created by Wendy Dalia, Leslie Driscoll, and Marsha Salett.
Last updated 5/14/98.