Structure of Benthic Macroinvertebrate Communities in a Midwestern Plains Stream

Abstract

Functional group structure of benthic macroinvertebrate communities was compared among three distinct reaches of the Redwood River, a plains stream in southwestern Minnesota. Deciduous leaf-fall comprised the allochthonous organic input to the upstream site, typical of a woodland stream; at the middle site, fine particulate organic matter, derived from soils in agricultural croplands, comprised the main allochthonous import; and at the lower site, soil-derived particulates and zooplankton from an impoundment comprised the main organic import. Mineral fine particulates, primarily silt, entered the stream during most of the year. The upstream site was most similar to other woodland streams in its functional invertebrate structure, with shredders and collectors both well represented. In the middle and downstream communities, collectors were quantitatively most important, with gatherers in depositional reaches and filterers in erosional reaches. Instability of physical habitat, influenced by heavy siltation from agricultural croplands appeared to favor a community of generalist collectors.