Comparison of the Impacts of Culverts versus Bridges on Stream Habitat and Aquatic Fauna

摘要

This project was an interdisciplinary look at the differences in impacts between culverts and bridges on stream habitat and stream fauna. There were four essential components: (1) Freshwater mussels: We took habitat measurements and conducted mussel surveys at 43 culverts across the piedmont in NC. Overall, habitat downstream of culverts was much more impacted than downstream of bridges. The reduction in mussel populations downstream of culverts was also more pronounced than at bridge sites. These effects were magnified in certain soil types that were more erodable. (2) Geomorphology: Detailed stream morphology and substrate measurements were taken at arch, pipe and box culverts and bridges. All crossing types were shown to increase stream cross-sectional area downstream by constricting flow at the crossing. (3) Toxicology: We conducted toxicity tests with polycyclic aromatic hydrocarbons (PAHs) on all life stages of freshwater mussels. We also assessed genetic damage due to PAH exposure. We found that PAHs are not acutely toxic to mussels but may possibly be contributing to long-term genetic damage. (4) Fish Passage: Fish community structure and passage was assessed at different crossing designs in the piedmont. There were no significant differences detected in community structure between crossing types. Though not statistically significant, data suggest a trend toward greater fish movement through bridges than culverts.