nurseries and food sources for young fish before they move out into open water. The microorganisms and vegetation in wetlands are essential on both local and global scales in cycling carbon, nitrogen, and sulfur between the earth and the atmosphere. In addition, wetlands provide commercial products such as lumber, cranberries, marsh hay, wild rice, waterfowl, muskrat, beaver, and mink.

Despite their benefits, wetlands in many parts of the world are disappearing at an alarming rate due to human activity. In the contiguous United States, more than 50 percent of the original wetlands had been destroyed by the 1970s, and an additional 2.6 percent were lost through the 1980s (Frayer, 1991). In some states—such as California, Ohio, and Iowa—less than 10 percent of the original wetlands remain, with consequent losses of waterfowl, furbearing animals, and fish.

The largest human uses of wetlands are for forestry and agriculture (Kivinen, 1980). Across large sections of the Midwest, for example, drainage tiles have been installed beneath wetlands to allow use of their fertile soils for crop production. Urban development also has led to the dredging and filling of many wetlands. Others have been flooded or drained by

Example of a wetland: a patterned peatland in the Hudson Bay Lowlands in Canada. Because of upwelling ground water, large peatlands such as this often develop intricate landscape patterns, which represent perhaps the most delicate mutual interaction between hydrology and vegetation on the earth's surface (Sjörs, 1961; Heinselman, 1963; Wright et al., 1992).

SOURCE: Paul H. Glaser, Limnological Research Center, University of Minnesota.