. The changing Illinois environment : critical trends : technical report of the Critical Trends Assessment Project. Man; Pollution; Environmental protection; Ecology; Environmental impact analysis. WETLANDS Urban Loss The loss and modification of wetlands as a result of urbanization is apparent in the nation and in Illinois. From the mid-1950s to the mid-1970s, urban develop- ment accounted for 8% of the wetland losses in the contiguous 48 states (Frayer et al. 1983). The loss of wetlands to urbanization continued in the United States between the mid-1970s and the mid-1980s (Dahl and Johnson 1
. The changing Illinois environment : critical trends : technical report of the Critical Trends Assessment Project. Man; Pollution; Environmental protection; Ecology; Environmental impact analysis. WETLANDS Urban Loss The loss and modification of wetlands as a result of urbanization is apparent in the nation and in Illinois. From the mid-1950s to the mid-1970s, urban develop- ment accounted for 8% of the wetland losses in the contiguous 48 states (Frayer et al. 1983). The loss of wetlands to urbanization continued in the United States between the mid-1970s and the mid-1980s (Dahl and Johnson 1991). In northeast Illinois, the Chicago District of the Army Corps of Engineers issued 372 wetland fill permits in 1992, compared with nine in 1983 (Dreher et al. 1988) (Figure 65). Most permit applications regarding wetlands and stream modifica- tion in the region of the Chicago District were granted, and the number of applications ranged from about 50 to 90 per year from 1982 to 1985 (Figure 66). FACTORS AFFECTING WETLANDS Although the loss of wetlands is of monumental importance, the biological, chemical, and physical degradation of wetlands by humans and the resultant decline in productivity and diversity of those wetlands remaining are also significant. Wetlands have been affected by many factors, including alteration of natural hydrological regimes (, drainage, dams, channelization, reservoirs), agriculture, urbanization, and nonpoint pollution, especially sedimentation. Sedimentation Erosion is responsible for removing 201 million tons (182 million metric tons) of soil each year in Illinois (Illinois Department of Agriculture 1992). Approxi- mately 35% of the 32 million acres (13 million ha) of rural land in Illinois requires some form of soil erosion control treatment. However, in 1990, Illinois led the nation in the number of acres of cropland planted with conservation tillage systems, which were used on of the state's cropland. Illinois also led the co
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