March, 1963 Larimore & Smith: Fishes of Champaign County 



355 



ly pollution-tolerant species might have 

 been absent because they did not occur in 

 the drainage system, because suitable habi- 

 tat was not available, or because they were 

 more sedentary in habits. The above list 

 of pollution-tolerant species contains most 

 of the species listed as tolerant by Thomp- 

 son & Hunt. 



DISTRIBUTION AND 

 WATER ENRICHMENT 



Stream enrichment is a vaguely defined 

 condition in which some of the dissolved 

 chemical constituents of the water are 

 greater in amount than would normally 

 occur from contact with the soil in a par- 

 ticular drainage system or region. Enrich- 

 ment of a body of water should result 

 in greater productivity of aquatic organ- 

 isms. However, because aquatic organ- 

 isms have rather specific requirements, en- 

 richment may produce conditions inimical 

 to their very existence. Enrichment to 

 some organisms is pollution to others. 



Champaign County streams are en- 

 riched by minerals leached from the soils 

 of the drainage area, by fertilizers added 

 to soils for increased crop production, by 

 wastes from livestock, and by domestic 

 sewage. Wastes from commercial opera- 

 tions could also contribute enriching ma- 

 trials, although no instance of such en- 

 richment is known to occur in this county. 



Natural Soil Fertility 



The soils of Champaign County are 

 unusually fertile and contribute dissolved 

 nutrients to the streams draining them. 

 The chemical composition of the waters, 

 table 3, has been discussed previously. 



Thompson & Hunt assumed that the 

 size of a fish population was related to 

 soil fertility because they found the larg- 

 est concentration of fishes in the East 

 Branch of the Salt Fork River, which 

 flows through an area that they regarded 

 as more fertile than any other in the 

 county. Presently available information 

 on the soils of Champaign County does 

 not indicate that the streams in this 

 drainage flow through an area more fertile 

 than other drainage areas of the county. 

 At only three of our collecting stations on 

 the East Branch was the weight of fish per 

 100 square yards much greater than the 

 average for the county, tables 14 and 26. 



Alkalinity and total hardness have often 

 been related to high productivity in nat- 

 ural waters. All of the streams in the 

 county are slightly alkaline and rather 

 hard. The water in one of the two main 

 streams in the East Branch drainage, the 

 Spoon River, is the hardest in the county 

 and one of the most alkaline, whereas 

 water in the other stream is the least 

 alkaline and near average in hardness, 

 table 3. Because of dififerences in chemical 

 composition of these streams, which pro- 

 duced several large fish collections and 

 were regarded by Thompson & Hunt as 

 especially fertile, it is difficult to relate 

 fish productivity to soil or water fertility. 

 The differences between these streams ap- 

 pear to be more the result of domestic 

 pollution than of soil characteristics in the 

 drainage area. 



Fertilizers on the Watershed 



Commercial fertilizers are used by 

 farmers on virtually all of the croplands 

 of Champaign County. The amount of 

 fertilizer that enters the streams is in- 

 fluenced by the natural soil chemistry, the 

 soil permeability, the land use, the kind 

 and amount of fertilizer applied, and 

 other factors that make an exact determi- 

 nation difficult. 



Large amounts of organic fertilizer in 

 the form of livestock manure are applied 

 by farmers to most of the watersheds. The 

 droppings of grazing cattle and hogs are 

 deposited in pastures, often along stream 

 banks, and sometimes actually in the 

 streams. In some areas, manure contributes 

 substantially to the fertility of the streams. 

 An excess of fertilizer can cause fish mor- 

 tality during the hot summer months 

 when the water levels are unusually low, 

 but, in Champaign County, instances of 

 damage caused by excess amounts of live- 

 stock manure are probably rare. Damage 

 is done by livestock when the animals 

 break down stream banks, permitting ex- 

 cessive amounts of silt to enter water 

 courses. 



Domestic Sewage 



Domestic sewage can be related to 

 stream productivity in several places in 

 Champaign County. Thompson & Hunt 

 in 1928 found a fish population in the 

 East Branch apparently benefiting from 



