organisms. In addition, we do not know to what extent the resuspension 

 of bottom sediments by barges in the main channel contributes to sedimen- 

 tation in backwaters and bottomland lakes. 



Biological, chemical, and sediment studies of Meredcsia Lake were 

 conducted in 1975 by the Illinois State Water Survey , the Illinois Natural 

 History Survey, and the Illinois Geological Survey for the Illinois Depart- 

 ment of Conservation and the U.S. Fish and Wildlife Service, which main- 

 tains a refuge at the lake. The sediment studies showed that Meredosia 

 Lake is filling with sediment from the lower end, where the lake first 

 becomes connected with the Illinois River when water levels rise from the 

 normal pool elevation. The Illinois River essentially backs upstream 

 into the lake when the water levels are at intermediate stages. When 

 the river is at flood stage or above, the water flows across the low 

 natural levees at the upper end of the lake, down through the lake, and 

 cut the downstream end. Butts (unpublished report, 1975: 7-8) found that 



the oxygen demand exerted by the sediment increased from the upstream end 



2 

 of the lake (2.58 grams /m /day, a value typical of an average polluted 



sediment in the main channel of the Illinois Waterway) to the downstream 



2 2 



end (4.32 grams/m /day, which approaches the 5.00 grams/m /day observed in 



the grossly polluted upper Illinois Waterway). When the bottom sediments 



at the downstream end of the lake were disturbed, the oxygen demand was 



86.08 grams/m /day, considerably higher than the demand observed anywhere 



else in the Illinois Waterway. In August 1974, the Natural History Survey 



found that oxygen levels in Meredosia Lake were 3 mg/1, while oxygen 



levels in the river on the same date were 6 mg/1. The readings were 



taken in the middle of the afternoon on an overcast day, and waves 



produced by a strong wind were resuspending bottom sediments in the 



lake. In the lake, a die-off of gizzard shad was occurring, and almost 



all the fingernail clams maintained in plastic cages on the bottom of 



the lake had died since they had last been checked in mid-July. The lake 



is devoid of submerged aquatic vegetation, and lakeshore residents have 



complained to their state legislators and to the Illinois Department of 



26 



