LAND USE AND STREAM ARCHITECTURE: PREDICTING MACROINVERTEBRATE COMMUNITY COMPOSITION BELOW STREAM CONFLUENCES.

B.J. Swisher¹, M.C. Watzin¹, N.J. Gotelli², J.P. Hoffmann³, G.G. Alexander¹, and D.M. Varney¹. ¹Rubenstein Ecosystem Science Laboratory, School of Natural Resources, University of Vermont, Burlington, VT 05401, ²Department of Biology, University of Vermont, Burlington, VT 05401, ³Department of Botany, University of Vermont, Burlington, VT 05401

Successful stream restoration requires that there are sources of appropriate colonists upstream from a restoration site. While the effects of agricultural land uses on stream biota are well documented, the interaction of land use and stream architecture is less well understood. Using an array of 13 sites throughout Vermont, representing four combinations of agricultural and undisturbed land use, we sampled the macroinvertebrate community upstream and downstream of stream confluences to assess the relative importance of land use, local habitat conditions, and potential colonists to the downstream community. Using a simple mixing model, we used relative abundances of taxa in the upstream reaches to predict their relative contribution to the downstream community. Downstream communities are most similar to the community in only one upstream reach at 7 of 13 sites. Among 6 sites with contrasting land use in upstream reaches, only four of the communities in downstream reaches most resemble the community in the upstream reach with similar land use. Although community composition below confluences generally reflects the total amount of agricultural land use upstream, sites with contrasting land use in upstream reaches have higher taxa richness than those with uniform upstream land use. These results suggest that local habitat characteristics may influence the degree to which macroinvertebrate communities below confluences are influenced by conditions upstream.