. The Changing Illinois environment : critical trends : summary report of the Critical Trends Assessment Project. Man; Pollution; Environmental protection; Ecology; Environmental impact analysis. 20 • The Changing Illinois Environment Physical damage to Illinois stream systems remains substantial. • Peoria Lake, the largest and deepest of the bottomland lakes on the Illinois River, lost 68% of its capacity between 1903 and 1985. Page 20 Figure 3-5 Mean Numbers of Indigenous Fish Species Per Sample in Champaign County Streams 25 20 - 15. 1890 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 Ha
. The Changing Illinois environment : critical trends : summary report of the Critical Trends Assessment Project. Man; Pollution; Environmental protection; Ecology; Environmental impact analysis. 20 • The Changing Illinois Environment Physical damage to Illinois stream systems remains substantial. • Peoria Lake, the largest and deepest of the bottomland lakes on the Illinois River, lost 68% of its capacity between 1903 and 1985. Page 20 Figure 3-5 Mean Numbers of Indigenous Fish Species Per Sample in Champaign County Streams 25 20 - 15. 1890 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 Hars hidicdte standard ermr^ Source: Ecological Resources, Illinois Ndrural Histor>' Sun'ey, 1994 mcreased more than 37% during those years, much of that occurring within 100 feet of the water. In Illinois' larger rivers, physical perturba- tions to the stream envi- ronment also come from within their banks. Propellers churn up bot- tom sediments, waves erode banks, dredging (to keep channels clear) and spoil-dumping physically reshape river channels and floodplain habitats. Since 1950 freight-carry- ing barge traffic statewide has increased fivefold (measured in tons), although the rate of increase overall has leveled off since 1980. The exact impact of barge traffic on river ecosystems is not understood but may he assumed to be substantial. While most soil erosion in Illinois occurs from open fields, most of the estimated 26,000 miles of Illinois streams also experience some enhanced erosion of their banks, especially where banks have been denuded of vegetation. The straightening or channel- ization of streams also increases their vulnerability to erosion by speeding the flow of water. How much of the sediment load of Illinois streams comes from their own banks varies with local conditions; estimates range from 20% to 80%. Streams also collect soil particles eroded from elsewhere in their watersheds. The Illinois River basin contains more than 60"o of the agricultur
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