Influence of agriculture on in-stream habitat and fish community structurein Piedmont watersheds of the Chattahoochee River System

Historical and contemporary fish collections were used to examine the influ ence of agricultural land use on fish communities in the central Chattahooc hee River, USA. In-stream habitat data were also collected to examine the r elationship between agricultural land use and stream habitat structure. We found a significant positive relationship between agricultural land use and in-stream sediment (r(2)=0.43, P=0.01). Stream depth heterogeneity decreas ed significantly with increased sediment (r(2)=0.39, P=0.02). Mainstream re aches draining agricultural lands had significantly lower levels of fish di versity than forested reaches (r(2)=0.47, P<0.01), Agriculture also explain ed significant variation in mainstream species abundances but was not a sig nificant predictor of species diversity or species abundances in headwater reaches. Most pool species that use coarse substrates decreased in relative abundance with increasing agriculture in the watershed. Our results sugges t that mainstream environments and their associated communities are more su sceptible than headwater reaches to the effects of agriculture. This findin g has important consequences for conservation, since mainstream reaches are reported to function as species refugia during pulse disturbance events (e .g., floods, droughts).