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:
Wetlands are defined -- or delineated -- according to three criteria  
Wetlands are categorized into five major systems

 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)


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.

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