observed significantly hgiher values for surface dissolved oxygen, 

 turbidity, and pH in the Mississippi, while mean total alkalinity was 

 higher in the Illinois. Mean total alkalinity in bottom water 

 was likewise higher in the Illinois, while bottom temperatures 

 were higher in the Mississippi. Of the 17 water quality factors 

 (including nutrients and toxic substances) measured in the surface 

 and bottom waters of the Illinois and Mississippi rivers by Colbert 

 et al. (1975: 43) only total phosphorus differed significantly between 

 the two rivers, being greater in the Illinois River. Since phosphorus 

 can stimulate blooms of blue-green algae, one might expect more blue- 

 greens in the Illinois than in the Mississippi, whereas just the 

 reverse was true. 



Significant differences between the two rivers in sediment con- 

 centrations of nutrients, metals, and toxic substances were noted by 

 Colbert et al. (1975: 46-47). Sediment in the Illinois River contained 

 more total phosphorus, iron, and ammonia than the Mississippi. Sediment 

 in the main channel of the Illinois contained detectable pesticide con- 

 centrations whereas none were detected in the main channel of the 

 Mississippi. PCB concentrations in sediment of the main channel 

 of the Illinois were greater than in the Mississippi. 



The phytoplankton populations in the lakes along the lower 

 Illinois River are probably much higher than in the river, due 

 to the lack of current and perhaps to some reduction in turbidity. 

 Butts (unpublished report, 1975: Table 3) found the average density 

 of phytoplankton in Meredosia Lake on August 7-8, 1975, was 1.7 

 million per liter and that diatoms and euglenoid algae dominated 

 in different parts of the lake. 



17 



