Assessing the Short-Term Effects of Lowhead Dam Removal on Contaminant Movement through Fish Food Webs in an Urbanized River System

Understanding how rivers change following dam removal is of increasing importance given the growing support of dam removal as a restoration strategy. In particular, the release and remobilization of sequestered contaminants following dam removal and their movement through aquatic food webs has not been well resolved, yet represents an important step in assessing short-term (< 2 yrs) impacts of dam removal. Here, we compare mercury (Hg), polychlorinated biphenyls (PCBs), and chlorinated pesticides in sediment, water, and fish food webs before and after two recent lowhead dam removals in the Scioto-Olentangy River system of Columbus, Ohio. Although sediment processing is in progress, water concentrations of Hg were similar in control reaches and reduced in experimental reaches (upstream and downstream treatments) following dam removal (but exhibited high within-site variability). Hg concentrations were not different before and after dam removal in insectivores, omnivores, or piscivores, although decreases in the relative abundance of large piscivores suggests that assemblage-wide bioaccumulation rates may decrease upstream of dam removal. PCBs and chlorinated pesticides are currently being analyzed. We anticipate that results from this work, when complete, will further our understanding of the interactions between fish food-web shifts and the release and transport of contaminants following dam removal.