USGS:  Science for a changing world


By Steven A. Frenzel
ABSTRACT: The Platte River drainage area from North Platte, Nebraska to Louisville, Nebraska currently is being investigated by the U.S. Geological Survey as a part of its National Water-Quality Assessment (NAWQA) Program. This program has an integrated approach to water-quality assessment involving the analysis of past and current physical, chemical, and biological data. Multivariate approaches to analysis may reveal underlying factors that contribute to observed biological attributes and increase the value of biological monitoring as a supplement to chemical-based water-quality monitoring.

Classification of 93 stream sites, based on macroinvertebrate data collected by the Nebraska Department of Environmental Quality in this central Nebraska study area, was done by using a clustering program developed for use with biological community data. Classification of sites based on their macroinvertebrate communities showed that four areas similar to previously defined ecoregions were not distinguished. Two groups of sites were identified from this classification; streams within or originating in the Sandhills formed a distinct group. To determine which environmental characteristics were most important in differentiating those macroinvertebrate communities, canonical correspondence analysis was used. Strong correlations among variables were common; for example, site altitude was correlated with precipitation (r=-0.93), percentage of drainage area in rangeland (r=0.87), average maximum soil slope (r=0.86), and average soil permeability (r=0.81). A forward-selection process of 17 environmental variables at 57 sites showed that stream width and soil permeability were most important in describing variance in the species-environment relation. Stream width may be indicative of the degree to which riparian vegetation affects macroinvertebrate community composition. Soil permeability was considered a surrogate for streamflow variability and predicatability. Soil permeabililty explained much more variability in community composition than did the percentage of sand in the stream substrate suggesting that macroinvertebrate communities in central Nebraska streams are affected more strongly by streamflow variability than substrate characteristics.

Frenzel, S.A., 1993, Multivariate analysis of macroinvertebrate communities and environmental variables in central Nebraska stream [abs.]: Platte River Basin Ecosystem Symposium, Grand Island, Nebraska, 1993, Program and Abstracts, p. 24.

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