Effects of Riparian and Watershed Land Use on Community Structure and Function in Headwater Streams

We examined nine headwater streams with a gradient of riparian forest buffer and watershed agriculture to determine the extent to which riparian buffers can ameliorate the effects of agricultural activities on stream ecosystems. Sampling was conducted seasonally over three years to explore temporal patterns in macroinvertebrate and fish assemblages related to land use, in-stream habitat, and water quality parameters.  Streams with low percent forest buffer had significantly higher daily maximum temperature, nitrate-nitrogen levels, and primary productivity than high forest buffer streams. Although there were greater abundances and biomass of macroinvertebrates and fish in streams with low forest buffer, assemblages were dominated by pollution tolerant taxa.  Streams with high percent forest buffer and low watershed agriculture had the best biotic integrity and the most complex trophic structure.  Ordinations based on fish assemblages indicated that streams sites grouped by land use category due to distinct differences in trophic patterns.  Stable isotopes analyses were also performed to examine trophic interactions and energy flow within each stream to determine how land use changes affect in-stream food web interactions.  Our results suggest that riparian forest buffers can reduce agricultural impacts on stream ecosystems and have implications for managing and restoring riparian areas in agricultural watersheds.