Physical and biological responses of streams to suburbanization of historically agricultural watersheds

Abstract

We investigated whether suburbanization influenced the physical and biological characteristics of ten 3rd-or 4th-order streams that drain historically agricultural watersheds in the southern Appalachians near Asheville, North Carolina. Five watersheds had areas of recent suburban development proximal to stream sites, and 5 watersheds were not currently undergoing suburban development. We estimated 5 hydrological, 10 geomorphological, 6 erosional, and 3 depositional (i.e., substrate) variables, and 13 fish and 8 macroinvertebrate metrics in the study sites. We used Student’s t-tests and multivariate analysis of variance to compare the 45 variables between sites in agricultural and suburban watersheds. We used Detrended Correspondence Analysis (DCA) to detect subtle differences in taxonomic composition and abundance among watersheds. Stormflow total suspended solids were significantly lower and substrate inorganic matter content was significantly higher in streams influenced by suburban development. Fish taxa richness and the density of nonguarding fishes were significantly higher in sites in suburban watersheds than in sites in agricultural watersheds. No other fish or macroinvertebrate metric differed with respect to watershed land use, but ordination of sites by fish and macroinvertebrate species abundance suggested that biotic assemblages at sites in suburban watersheds were distinct from those at sites in agricultural watersheds. Therefore, some taxa may have been influenced by suburban development. Our results suggest that watershed hydrology, sediment delivery, and sediment composition might be important factors influencing biota in streams draining agricultural vs suburban watersheds. Biological assemblages in streams differed structurally with respect to watershed land use, but streams did not appear to be otherwise influenced by suburban development. We conclude that suburbanization near historically agricultural southern Appalachian streams induces subtle changes to inorganic sediment dynamics, substrate composition, and fish and macroinvertebrate assemblage structure.