GEOMORPHIC AND HUMAN INFLUENCES ON STREAM QUALITY IN THE SOUTHERN APPALACHIANS

Human alterations of the landscape (e.g. agriculture, urbanization, channelization) clearly influence stream quality in the Southern Appalachian province, where streams harbor some of the highest levels of species diversity and endemism in the world. However, recent data indicate that evaluations of stream quality should be couched within the geomorphic context of the stream and its catchment. This paper illustrates the importance of geomorphic variables (e.g. gradient, bed texture, bedrock type, relief) with examples from the Piedmont and Blue Ridge provinces.

Geomorphic and land cover data were collected from more than 30 streams draining 10-130 sq km basins in northern Georgia and western North Carolina over a wide range of landscape settings. These data were used as independent variables to predict biotic quality expressed by various measures of fishes and macroinvertebrates collected at the same sites. Hundreds of geomorphic and land cover variables were tested as correlates of biotic quality by ordination, correlation, and multiple regression techniques. A methodological goal was to determine physical "indicators" of biotic quality.

Results indicate that many natural geomorphic variables (ones that lack human influence) are strong correlates of biotic quality at both the basin scale (e.g. ruggedness factor, relief, rock type) and reach scale (e.g. gradient). These data provide strong empirical evidence for Montgomery's (1999) "Process Domains Concept" (PDC), but fail to support the more widely known "River Continuum Concept" (Vannote et al., 1980) due to the narrow size range of catchments. The PDC posits that spatial variability in geomorphic processes governs stream habitat and disturbance regimes that influence ecosystem structure and dynamics. Results suggest that geomorphic conditions limit the capacity for biotic quality, and therefore certain geomorphic variables should be incorporated into stream quality assessments.

References Cited

Montgomery, D. 1999. Process domains and the river continuum. Journal of the American Water Resources Association 35 (2), 397-410.

Vannote, R.L., Minshall, G.W., Cummins, K.W., Sedell, J.R., and Cushing, C.E. 1980. River continuum concept. Canadian Journal of Fisheries and Aquatic Sciences 37 (1), 130-137.