Domestic sewage and industrial wastes are not the 

 only source of organic ]jollution of our streams. With 

 the development of larger and larger cities, the paving 

 of more streets, parking areas, etc., the storm water 

 runofT adds a considerable amount of organic matciial. 

 A study by Wcibel, Anderson. & Woodward (1964) of 

 a sewered storm water runofT from a 27-acre, residential- 

 light commercial area in Cincinnati, Oiiio, disclosed that, 

 assuming a secondary sewage treatment plant effluent 

 at the population density and environmental conditions 

 of this area, the o.xygcn demand of the storm water 

 would equal about 60 percent of the oxygen demand of 

 the sewage effluent on a yearly basis. 



Man is contributing other things to the Illinois 

 River. No one knows what all of these contributions 

 are, in addition to those from industry and farming op- 

 erations, or what they do to the environment. Usually 

 these additions come to the attention of biologists only 

 when there is a conspicuous deterioration of the biolog)' 

 of a stream. 



Occasional accidents occiu" which affect the biology 

 of the ri\er, as, for example, when large quantities of 

 ammonia fertilizer inadvertently escaped into it below 

 Peoria in 1961. 



With all that we are adding to the Illinois River, tin- 

 known and the unknown, it is certain that the river is 

 changing, and in some cases it is deteriorating rapidly 

 insofar as it affects the well-being of the animals and 

 plants that are dependent on it. 



The following pages include a summary of some of 

 our observations on this important stream. While we 

 discuss some chemical and physical parameters to this 

 problem, we are basically interested in them as they 

 affect the fish and wildlife. It is probable that a greater 

 future emphasis on the biology of streams will be a 

 necessity in any intelligent water management program. 

 Without in any way detracting from the importance of 

 other fields of specialization, we believe that water biol- 

 ogy stands at the center of any water quality consider- 

 ation. In the words of Hynes (1961), "Pollution is. 

 after all. primarily a biological phenomenon, as the 

 things we need to know about water are almost all con- 

 cerned with living organisms. Can we or our animals 

 drink it? Will it be a good medium for brewer's yeasts? 

 Is it likely to carry disease? Will it smell nasty as the 

 result of biological degradation of organic matter? Can 

 fish live in it?" 



TURBIDITY 



As mentioned previously, the Illinois River was at 

 one time characterized as being clear. It has always 

 carried some silt load, of course, but prior to human 

 settlement of the basin this must surely iiave been a 

 nominal one, and doubtless was most obvious during 

 periods of high water. When the while settlers estab- 

 lished the intense agrarian culture in the area, their 

 plows and axes began a change in the river which still 



goes on. Kofoid (1903:179) discussed the matter of 

 clarity as it was in 1896. He measured clarity by sub- 

 mciging a white plate of scmiporcelain. The depth at 

 which this plate disappeared from view was measured 

 in centimeters. 



"As might be expected in the river environment," he 

 stated, "when floods occur the tmbidity is often extreme, 

 and is exceedingly variable according to the locality and 

 the river levels. The extreme range of our records 

 extends from 1.3 cm. ['A inch], in a Spoon River flood, 

 to 260 cm. [8'/? feet], in Quiver Lake, under the ice. 



"In the [Illinois] river the great majority, about two 

 thirds, of the records lie between 20 and 50 cm. [8-20 

 inches], while the extreme range is from 2 cm. [% inch], 

 in the flood of May 1897, to 1 15 cm. [45 inches], in the 

 declining waters of July, 1896." The range for two-thirds 

 of his readings would be roughly estimated to equal 

 25-103 turbidity units (Jackson 1954:39). 



Recent turbidity measurements have revealed how 

 much greater the silt load is in the waters of the ri\er 

 than it was about 70 years ago. In 1963 and 1964, 

 during periods of minimum flow when the silt load 

 would be lowest, the turbidity was determined to be 

 from 79 to 220 units in the La Grange Pool. Thus at 

 this low-river stage, the modern measurements were 

 at the lowest reading three times those of Kofoid's and 

 at the highest reading over twice the 1896 (igme. We 

 have already discussed in general terms what this silt 

 load is doing to water impoundments, and its relation- 

 ship to modern agriculture. The lower and middle 

 stretches of the river tend to be kept in a more turbid 

 condition because of the movement of tow boats up and 

 down the main stream (Starrett, unpublished). Tin- 

 increased turbidity of the Illinois River has come from 

 the greater exposure of the soil to precipitation and 

 resulting erosion, as discussed in the previous section, 

 and from the hastening of the How of the nmddy wateis 

 into the stream. Great marshes, for example, used to 

 impede the movement of rainfall to the ri\er. hut these 

 marshes are largely gone now. 



That the silt load in the lower river tends to be 

 greater than in the upper stretches is indicated in the 

 following tabulation which lists the turbidity units by 

 navigation pools, beginning with the Alton Pool at the 

 river's mouth and ending with the Dresden Pool in the 

 Des Plaines River just below Chicago. 



Narigalion Raii^r in 



Pool Turbidily Units 



Alton 71-320 



La Grange 79-220 



Peoria 15-140 



Star\-cd Rock 1,5-52 



Marseilles 15-28 



Dnsclcn 15-27 



These readings were made during the periods of min- 

 imum flow in the fall months of 196!^ and 1964. During 

 j)eriods of high water all of these readings would, of 



L 



