Bottom
Fauna
Due to the changes in water levels and water quality, dramatic changes occur to the small bottom invertebrate fauna of the Illinois River. Robert Richardson of the Natural History Survey examines these changes in an area between Chillicothe, approximately 10 miles north of Peoria, and Brownville, approximately 63 miles south of Peoria. He examines the changes from a period of 1913-15 and 1920 (Richardson 1920).
Richardson finds that while the composition of the bottom fauna in 1915 is normal at Chillicothe, by 1920 the data show dramatic changes in the northernmost and southernmost sections of the study area, including reductions in numbers and poundage of the species that remain, and the elimination of numerous families and species. In addition, north of Havana he finds large numbers of species that are tolerant to pollution. He concludes that, assuming Chillicothe represents the “upper limit of wholesome conditions” in the bottom mud in 1915, then the pollution has affected an additional 80 miles of river, a full 16 miles for each of the five years being examined.
Richardson finds deteriorating conditions in the bottom of the river at all 35 lake and river stations between Chillicothe and Wesley. In 1915, Richardson notes “bubbling and more ore less foul odors” for some stations between Peoria and Chillicothe; whereas, in 1920, there is the wholesale disappearance of entire families and numerous genera and species of small bottom-animals, as well as the intrusion of pollution-tolerant species. He also finds the almost complete “disappearance of the aquatic vegetation which formerly covered several square miles of shallow-lake territory at low water.”
Richardson describes the mud samples taken from the bottom of the river at Rome and Spring Bay, just north of Peoria, as being a “peculiarly spongy and foul-smelling mud.” He further describes these mud samples as having a “texture not unlike freshly risen bread,” which makes a “distinct blubbering sound on being pressed with the hand as they lay in the tray.” In the samples from the lower lake, below the sewers, businesses, and residences of Peoria, Richardson finds conditions somewhat better than those north of Peoria, but “bubbling was abundant,” and at all stations, the dead shells of snails are blackened or otherwise discolored.
Richardson identifies three principal changes to the bottom fauna in the area just north of Peoria:
