Effects of Lowhead Dams on Prosobranch Snails in Illinois

Numerous studies have addressed the effects of dams on fishes, freshwater mussels, and aquatic insects, but few have examined the effects on aquatic gastropods. I established four site-types centered around four lowhead dams and sampled habitat variables and aquatic gastropods once a summer from 2008 through 2011. Multivariate analysis of variance indicated that habitat varied immediately upstream and downstream from the dams, with resultant effects on gastropod fauna. Compared with reference sites, impounded areas had greater depths and silt deposition and less diverse substrate composition, substrate stability, and hydrologic diversity and sites immediately downstream from the dams had less substrate diversity and silt deposition and larger mean substrate size. Gastropod densities were lower in these areas than reference sites.The data collected during this study contributes insights into the effects of lowhead dams on riverine habitat and aquatic gastropods assemblages in the Midwest