Effects of riparian forest buffers and agricultural land use on macroinvertebrate and fish community structure

Abstract

Although forested riparian buffers can improve stream habitat, there remains debate as to whether biotic integrity can be maintained by buffers in highly degraded watersheds. To determine if forest buffers can ameliorate cropland impacts, we examined macroinvertebrate and fish assemblages in headwater streams categorized into three land use groups (High Buffer-Low Agriculture, High Buffer-High Agriculture, Low Buffer-High Agriculture). Sampling was conducted seasonally over 3 years to explore temporal patterns in biotic assemblages related to land use, instream habitat, and water quality parameters. Macroinvertebrate and fish abundance were higher in low buffer streams due to large numbers of pollution tolerant taxa and herbivores that proliferated with increased periphyton. In contrast, High Buffer-Low Agriculture streams had the best biotic integrity likely due to increased depth and better habitat quality. Non-metric multidimensional scaling ordinations of macroinvertebrate taxa showed no separations, but fish communities were significantly different among all three land use groups. Findings suggest fish community structure is more sensitive than macroinvertebrates to agricultural influences at both the riparian and watershed scales. Our study provides information on the effects of riparian vegetation on agricultural stream communities and highlights the importance of managing riparian forests to conserve stream biotic integrity.