Robert Davis' Graduate Defense Seminar

A Graduate Defense Seminar iwll be given by Robert P. Davis, MS Candidate in Ecosystem Science. His seminar will be Shifts in Sediment Dynamics and Food-web Structure Mediate Fish Contaminant Body Burdens Following Lowhead Dam Removal. This seminar will be held at the Olentangy River Wetlands Research Park in 101 Heffner Wetland Research and Education Bldg.

Lowhead dams fundamentally alter physical, chemical, and biological properties of rivers. Dams store sediments in the upstream reservoirs, and are thought to sequester persistent contaminants as well, although this is not well documented relative to lowhead dams. Here, I investigated changes in fish body burdens of mercury (Hg), selenium (Se), polychlorinated biphenyls (PCB), and chlorinated pesticides (e.g., dieldrin) before and after two lowhead dam removals in the Scioto and Olentangy Rivers in Columbus, Ohio. I also investigated relationships between sediment Hg concentrations and detection rates in fish. This study utilized a modified before-after-control impact- (BACI) design with various treatments (e.g., control, upstream/ downstream, restored/unrestored, before/after). Fish surveys were conducted prior to dam removal at four of seven study reaches, and at all study reaches post dam removal.  Sediment collections were conducted for 2-3 years post dam removal at all sites. For most contaminants considered, fish body burdens converged across study reaches by the last year of the study in both rivers. In general, PCB, dieldrin, and aldrin fish body burdens decreased through time.  Hg detection rates in fish were not significantly different before or after dam removal or among study reaches during the duration of the study. Fish contaminant body burdens in the upstream restored and unrestored reaches in the Olentangy River responded similarly through time, but were higher in the unrestored reach post dam removal in years 1-3 combined. No upstream-downstream differences were observed in body burdens in the Olentangy River, but aldrin and dieldrin body burdens were higher downstream than upstream of the removed dam in the Scioto River following dam removal. The strongest relationships between trophic position and contaminant body burdens were observed with PCBs and Se in the Scioto River, and dieldrin in the Olentangy River. Food-chain length was significantly related to mean aldrin body burdens, but was not related to mean PCB, dieldrin, or Se body burdens or Hg detection rates. Hg sediment concentrations were not correlated to Hg detection rates in fish. Taken as a whole, these findings represent one of the first studies to document ecosystem contamination following dam removal and will be useful in informing future dam removal efforts.

Mazeika Sullivan, advisor