Effects of land use and seasonality on community and food web structure in headwater streams

We examined nine headwater streams with a gradient of riparian forest and agricultural land use to determine the effect of riparian and watershed land use on stream communities. 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. While there were significant seasonal and annual differences, relationships among streams with different land use types were relatively consistent. Macroinvertebrate and fish abundance and biomass were significantly higher in streams with low percent riparian forest compared to streams with high percent riparian forest. Macroinvertebrate HBI and fish IBI scores improved with increasing percent riparian forest suggesting better stream water quality with increasing forest buffer. Streams with the highest percent forest buffer and lowest percent watershed agriculture had the highest biotic integrity, greatest abundance of pollution-sensitive species, and the most complex trophic structure. 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 communities and have implications for managing and restoring riparian areas in agricultural watersheds.