Monday, May 26, 2008 - 3:30 PM
106

Path analyses to assess the effects of nutrients, light and sediment fines on periphyton and on invertebrate and fish metrics

Michael B. Griffith, National Center for Environmental Assessment, U.S. Environmental Protection Agency, Office of Research and Development, 26 W. Martin Luther King Drive, Cincinnati, OH 45140 and F. Bernard Daniel, National Exposure Research Laboratory, U.S. Environmental Protection Agency, Office of Research and Development, 26 W. Martin Luther King Drive, Cincinnati, OH 45140.

Biological impairments in streams are typically defined by altered invertebrate or fish assemblages.  While nutrients and canopy cover contribute to these impairments, these stressors are generally defined by changes in periphyton.  Path analysis can extend these assessments to effects on invertebrates and fish by characterizing the direct and indirect relationships among variables along defined model pathways. With data from tributaries of the Little Miami River, we tested models of the effects of nutrients (total N, total P and N/P ratio), % open canopy and % sand and fines on periphyton and, in turn, on invertebrate or fish metrics.  The results suggest direct and periphyton-mediated pathways for effects on invertebrate and fish metrics.  All periphyton metrics increased with open canopy.  Over the N gradient, algal ash-free dry mass (AFDM) increased, while % cyanobacteria decreased.  Along a sediment fines gradient, % cyanobacteria also decreased, but % Chlorophyta increased.  The % predators, Trichoptera and herbivorous fish increased with algal AFDM, while % climbers and darters & sculpins decreased.  The % predators and Trichoptera decreased with % cyanobacteria, whereas % Trichoptera increased with % Chlorophyta.  This effort illustrates how path analysis can be used to explore responses resulting from stressors with interacting effects.


Web Page: nutrients, periphyton, faunal assemblages

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