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"
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.
are defined -- or delineated -- according to three criteria
water-tolerant plants that have adapted to wetland conditions
hydric soils: water-saturated
soils that have become oxygen deficient
dominated by the presence of water through flooding or saturated ground
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
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
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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