Potential impacts of small dam removal on fish and mussel communities in North Carolina

Abstract

As many small dams exceed their structural life expectancies, dam removal is becoming a priority to safeguard aquatic ecosystems against potential failures. While this restoration tool improves habitat connectivity and water quality, there are also several costs associated with it such as potential impairment of freshwater mussel communities. Such risks are of great concern in North Carolina, which has one of the highest small dam densities in the U.S. and is a hotspot for endangered and threatened mussels. To help characterize potential impacts, this research paper provides a literature review of mussel and fish responses to dams and dam removal and an evaluation of monitoring reports from past projects. The results suggest that ecological rebound following removal may depend on the degree to which resulting discharges and sediment loads correspond with historic floods. Moreover, both project design and monitoring efforts should better incorporate habitat tolerances and life histories of sensitive species present at specific project sites. When resources limit monitoring efforts, sampling should occur in un-impounded waters where substrates are consolidated, and adequate distances downstream where dam impacts on species abundance and richness are minimal. The timing of post-removal monitoring should also be guided by visual surveys, and by specific habitat preferences of project target species.