Effects of lowhead dams on fish and benthic invertebrate assemblage structure in the Neosho River, with comments on the threatened Neosho Madtom, Noturus placidus.

Abstract

Many studies have assessed the effects of large dams on fishes and benthic invertebrates, but few have examined the effects of lowhead dams. I sampled fishes, benthic invertebrates, habitat, and physicochemistry monthly from November 2000 to October 2001 at eight gravel bar sites centered around two lowhead dams on the Neosho River, Lyon County, Kansas, including a reference site and a treatment site upstream and downstream from each dam. Multivariate analysis of variance indicated site type differences for habitat, and benthic invertebrate and fish abundance, but not physicochemistry, through there were site type*dam interactions for habitat, and benthic invertebrate and fish abundance, and site type*month interactions for benthic invertebrate and fish abundance. Analysis of variance indicated that none of the measured physicochemical variables differed among site types; however habitat did vary immediately upstream and downstream from the dams, as did benthic invertebrate and fish abundance. Compared to reference sites, upstream treatment sites were deeper with slower velocity, downstream treatment sites were shallower with faster velocity, and both treatment site types had greater substrate compaction. Benthic invertebrate abundance was lower at downstream treatment sites than other site types. Benthic invertebrate richness did not differ, but upstream treatment sites had lower evenness than other site types. A lower proportion ofephemeropterans, plecopterans, and trichopterans (%EPT) inhabited treatment sites than reference sites. I found more fish in downstream reference sites and fewer in treatment and upstream reference sites. Fish species richness did not differ between site types, but upstream site types had higher evenness than downstream site types. Abundance of Neosho madtom, Noturus placidus, was significantly lower immediately upstream and immediately downstream from dams compared to reference sites, whereas abundances ofsuckermouth minnow, Phenacobius mirabilis, orangethroat darter, Etheostoma spectabile, and slenderhead darter, Percina phorocephala, were higher in downstream treatment areas than reference sites. The apparent effects of these lowhead dams on fish and benthic invertebrate assemblages were similar to the effects reported for larger dams.