PART III: RESULTS 

 Physical-Chemical Measurements 



The data for water temperature, dissolved oxygen, and transparency 

 obtained in 1974 are given in Table 2. 

 Water temperature 



The water temperatures in Starved Rock, Marseilles, and Dresden 

 Pool were generally higher than in the upper part of Peoria Pool, even 

 though the readings in the upper pools were taken two weeks later and 

 the weather had turned colder. The upper river is evidently warmer be- 

 cause of warm industrial and municipal discharges. Starrett (1971) re- 

 ported the same trend of warmer temperatures in the upper river in July 

 and August, 1966; Butts, et al. (1975) report data collected in 1971 

 which show that the mean temperature profile of the Upper Illinois and 

 Des Plaines Rivers was significantly increased by thermal discharges 

 near Joliet (mile 284.0). 

 Dissolved oxygen 



Since the DO levels at both the 3-ft depth and at the bottom were 

 approximately the same within each station, the water was presumably 

 well-mixed. 



In the Lower Illinois (Alton Pool), the DO concentration was 77 to 

 97 percent of saturation ; in the Middle Illinois 



(LaGrange and Peoria Pools) , it ranged from 56 to 122 percent of satura- 

 tion; and in the Upper Illinois (Starved Rock, Marseilles, and Dresden 

 Pools), it ranged from 47 to 104 percent of saturation. 



The untypically high oxygen values exceeding saturation at Ballard 

 Island Chute and in Lower Peoria Lake were probably due to algal photo- 

 synthesis, which was also indicated by the greenish or brownish color 

 of the water. Ballard Island Chute is shallow and, with its large sur- 

 face area, slow current, dissected shoreline, and numerous marshy 

 pockets, provides an environment suitable for phytoplanktonic develop- 

 ment. 



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