Monday, June 4, 2007 - 1:00 PM
8

Macroinvertebrate Assemblage Patterns and Streamflow Characteristics Across the Western United States

Anne M. D. Brasher, Utah Water Science Center, U.S. Geological Survey, 121 West 200 South, Moab, UT 84532, Chris P. Konrad, Washington Water Science Center, U.S. Geological Survey, 934 Broadway Street, Tacoma, WA 98402, and Jason T. May, California Water Science Center, U.S. Geological Survey, 600 J. Street, Placer Hall, Sacramento, CA 95819.

The goal of our study was to describe influences of streamflow patterns on macroinvertebrate assemblages.  Continuous discharge records from 115 sites in 11 Western States were used to calculate streamflow metrics.  Metrics were selected to represent magnitude, duration, frequency, timing, and variability during three levels of flow: high, low, and central tendency.  Quantitative macroinvertebrate samples from each of the sites were used to calculate metrics of macroinvertebrate community structure including abundance, richness, diversity, evenness, functional feeding groups, and relative abundances of specific taxa. We used a nonparametric screening procedure to identify relations between streamflow metrics and macroinvertebrate assemblages. Quantile regression provided a quantitative assessment of the influence of streamflow on upper and lower limits of macroinvertebrate assemblages. Streamflow variability was associated with the largest number of macroinvertebrate metrics.  Associations of macroinvertebrate metrics with daily streamflow variability were inverse to associations with monthly variability.  Variability in flows was associated with macroinvertebrate abundance, richness, and diversity.  Magnitude of high flows was associated with relative abundance and richness of EPT taxa and non-insect taxa, while the frequency of high flows was associated with dominant taxa, diversity, and evenness. These analyses may be useful for developing models to predict biologic response to hydrologic modifications.

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