Forested riparian buffers have been shown to improve stream water quality in agricultural watersheds by reducing soil erosion and filtering runoff before it enters the stream. While previous studies have addressed the size and width of riparian buffers needed to reduce agricultural pollutants, more research is needed to determine how much riparian vegetation is sufficient to ameliorate the effects of agricultural activities on stream community structure and ecosystem function. In this study, we examined eight agricultural streams with a gradient of riparian forest (92%-16%) to determine the effect of riparian and watershed land use on stream biological communities. Sampling for this study was conducted seasonally for two years. Macroinvertebrate and fish biotic metrics were used to examine community differences related to land use, in-stream habitat, and water chemistry parameters. In addition to evaluating community composition, differences in stream metabolism among sites were investigated as an assessment of land use effects on ecosystem function.
Results/Conclusions
Spearman correlation and redundancy analyses were used to examine relationships among biotic metrics and environmental characteristics. Preliminary analyses suggest that biotic metrics are sensitive to agricultural influences at both the riparian zone and watershed scale. Macroinvertebrate Hilsenhoff scores (HBI), taxa richness, and diversity (Shannon's H') were negatively associated with watershed agriculture and positively associated with riparian forest. While percentage of watershed agriculture had the strongest correlation with most biotic metrics, metrics scores improved with increasing percentage of riparian forest. Our results provide information on the influence of riparian vegetation on the structure and function of stream ecosystems and highlight the importance of restoring riparian areas in agricultural watersheds.