EVOLUTIONARY PROCESSES OF INCISED STREAMS IN THE SHADE RIVER BASIN, SOUTHEASTERN OHIO: IMPLICATIONS FOR HABITAT QUALITY AND STREAM HEALTH

Stream channels in the Western Allegheny Plateau (Level III Ecoregion 70) display varying degrees of instability associated with channel incision, scour of channel banks (with and without mass wasting), and aggradation. In the Shade River basin of southeastern Ohio channel instability is widespread and moderately severe, contributing to impairment of water quality. We used process-based rapid geomorphic assessments to quantify channel instability in the Shade River basin, and coupled it with sediment, fish, and aquatic macroinvertebrate surveys to: (1) examine potential linkage between channel instability and channel-bed texture, and (2) explore the degree to which channel instability affects metrics of biological integrity. Early results suggest a positive relation between channel instability and indices of biological integrity for fish and aquatic macroinvertebrates, particularly at sites that are in active aggradation phases. At these sites deposition of sediment sheets within incised channels provides raw material for the generation and recovery of naturalistic bed- and barforms. Bed texture varies among sites, but is not obviously linked to localized differences among channels in evolutionary states and trajectories. Channel instability scores appear to account for more variation of biological integrity among unstable streams than the more widely applied Qualitative Habitat Evaluation Index (QHEI). These results raise fundamental questions concerning the assessment and ecological impacts of sedimentation, and further underscore the need to include geomorphic processes in the diagnosis and treatment of water-quality impairment.