Response of Aquatic Biota to Changing Land Use Pattern in Streams of West Georgia, USA
Type of DegreeDissertation
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Watershed land use change is one of the most pervasive influences facing streams in the southeastern United States. In particular, watershed urbanization has a potentially dramatic impact on stream biota. Through direct alteration of several interrelated instream processes including hydrology, geomorphology, and physicochemistry, land use change can indirectly influence stream biotic composition and quality. Starting in 2002, I examined aquatic biotic responses to changing watershed land use/cover (LU/LC) and subsequent abiotic alterations in the Lower Piedmont ecoregion north of Columbus, Georgia, USA, in 25 small streams (2 3rd order) whose watersheds (500 2500 ha) varied in their degree of urbanization, residential development, pasture, managed and unmanaged forest cover. Benthic macroinvertebrates, as taxa richness and Shannon’s diversity (H’), were negatively associated with increasing urban cover, peak stream discharge, and water temperature, and positively associated with increasing forest cover and dissolved oxygen (DO) levels. Further, macroinvertebrate biomass increased while seasonal variation decreased with increasing urban cover. Fish assemblages were largely explained by a combination of land use and landscape (stream hydrology, geomorphology) variables that vary seasonally, with stronger land use signals in the summer and a stronger fish response to landscape variables in the winter and spring. Fish assemblages shifted from cyprinid-based in forested (managed and unmanaged) and pasture watersheds to centrarchid-based in urban and suburban watersheds; this shift was correlated with increasing spate frequency, stream temperature and decreasing DO. Stable isotopes analyses revealed food webs in watersheds with increased LU/LC disturbance were significantly different than food webs in forested watersheds. Further, overall food chain length and mean trophic position decreased with increasing impervious surface. Specifically, food chain length increased with stream habitat quality whereas chain length and mean trophic position decreased with increasing maximum stream discharge and duration of high flows. My results suggest that changing land use exerts multiple direct and indirect stressors on stream biota that vary depending on the biology of the organism or assemblage under consideration. Specifically, streams in urbanized watersheds are harsh environments that have less diverse assemblages dominated by few tolerant taxa, minimal seasonal variation, and simplified food webs.