a July mean of 6.6 mg/1 during a high river stage and a September mean of 

 9.3 mg/1 during an average river stage. They found that dissolved 

 oxygen saturation values were generally lower in all habitats during 

 July and complete oxygen saturation was observed only during September 

 (Colbert et_ al . , 1975: 35). No dissolved oxygen concentrations during 

 1974 fell below the minimum Illinois and Missouri stream standard of 

 5 mg/1 (Colbert et al. , 1975: 35). 



From a comparison of available pre- and post-construction dissolved 

 oxygen data, it appears that the nine-foot navigation system has had 

 no measurable effect on this water parameter. 



Turbidity, Suspended Sediment, and Water Clarity . McKee and Wolf 

 (1963: 290) stated that the turbidity of water is attributable to sus- 

 pended and colloidal matter, the effect of which is to reduce clearness 

 and diminish the penetration of light. Bellrose et al. (1977: C-42) 

 reported that agricultural pollution (soil runoff) was probably the 

 greatest factor contributing to high turbidity levels in the Illinois 

 River. Other factors listed were resuspension of bottom sediments by 

 barge traffic, bank erosion from boat-produced wakes and wind-produced 

 waves, and feeding activities of fish (Bellrose et al., 1977: C-42). 

 The greatest effect of high turbidity levels in freshwater systems is 

 the restriction of sunlight needed for photosynthesis by aquatic plants. 

 The effects of turbidity on aquatic plant production have been well 

 documented (Martin and Uhler, 1939: 120; Low and Bellrose, 1944: 17; 

 Chamberlain, 1948: 352; Robel, 1961: 437, and Bellrose et al. , 1977: 

 C-43). 



Hooker (1897 in Galtsoff, 1924: 371) reported that suspended 

 sediment (surface) levels in the period 1880-1881 in the upper Mis- 

 sissippi River from Winona, Minnesota (Mississippi River mile 725.0) 

 to Hannibal, Missouri (Mississippi River mile 309.0) ranged from 34 to 

 165 ppm, with increasing levels downstream. Hooker found that at 

 St. Louis (Mississippi River mile 180.0) the suspended sediment con- 

 centration was 686 ppm, which he attributed to the influence of the 

 Missouri River; in 1879, the Missouri River contained 2,418 ppm sediment 



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