An application of bioassessment metrics and multivaraite techniques to evaluate central Nebraska streams

Ninety-one stream sites in central Nebraska were classified into four clusters on the basis of a cluster analysis (TWINSPAN) of macroinvertebrate data. Rapid bioassessment protocol scores for macroinvertebrate species were significantly different among sites grouped by the first division into two clusters. This division may have distingusihed sites on the basis of water-quality impairment. Individual metrics that differed between clusters of sites wre the Hilsenhoff Biotic Index, the number of Ephemeroptera, Plecoptera, and Trichoptera (EPT) taxa, and the ratio of individuals in EPT to Chronomidae taxa. Canonical correspondence analysis of 57 of the 91 sites showed that stream width, site altutide, latitude, soil permeability, water temperature, and mean annual precipitation were the most important environmental variables describing variance in the species-environment relation. Stream widith and soil permeability reflected streamflow characteristics of a site, whereas site altitude and latitude were factors related to general climatic conditions. Mean annual precipitation related to both stream-flow and climatic conditions.