Freshwater wetlands can mean many different
things. To some, the vitality and beauty of marshes can only be
described and captured in words and pictures. At the opposing
extreme, urban engneers and planners see wetlands as unused space
that can be exploited for drainage or as the possible receptacle of
human waste products. To the ecologist, freshwater wetlands are
complex systems. To past farmers and countryfolk they have
generally represented an extremely important renewable
resource. This view is returning as culivation of crops for
the mass production of energy becomes profitable.
Ecological definitions vary markedly from marshes
of glacial origin, to prairie wetlands, to freshwater marshes of
estuarine areas that experience severe fluctuations in water
movement under tidal influences. In glaciated regions, marshes are
often remnant wetlands of shallow lake systems in which vegetation
extends over the entire water surface. Technically a swamp or bog
contains persistent standing water among the vegetation, whereas
marshes contain water-saturated sediments with no or little
standing water among the vegetation. The conditions of wetlands
change markedly and rapidly in response to fluctuations in climate
and rainfall. Many of these responses are cyclical with long-term
periods.
All of these defining features of freshwater
wetlands makes them good educational models for understanding the
inerplay between culture and ecology, where the emphasis is on
managing systems of biological productivity in relation to water
and nutrient flows.