Graduate Program

Biological Sciences

Degree Name

Master of Science (MS)

Semester of Degree Completion

2012

Thesis Director

Karen F. Gaines

Thesis Committee Member

James M. Novak

Thesis Committee Member

Jill L. Deppe

Abstract

The Department of Energy's (DOE) Savannah River Site (SRS) is a 777 km2 former nuclear weapon material production and current research facility located along the Savannah River in west-central South Carolina. In 1954, direct environmental discharges were released from "M-Area", a fuel and aluminum-clad Uranium (U) nuclear reactor target manufacturing facility through a drainage ditch into the Tims Branch-Steed Pond water system. The wastewater discharges released into Tims Branch contained large volumes of inorganic wastes including depleted and natural U, aluminum (Al), and Nickel (Ni) along with smaller quantities of mercury (Hg), lead (Pb), copper (Cu), chromium (Cr), and zinc (Zn). The Tims Branch black water system is a second order stream currently containing ≥ 7 beaver impoundments located in the northwestern region of the Savannah River Site (SRS). The purpose of this investigation was to better understand the current dynamics of the Tims Branch water system within an ecological risk assessment framework by examining metal concentrations, bioavailability and trophic transfer of contaminants in lower trophic level biota in 7 beaver-impounded ponds. Biofilm, detritus, Anuran and Anisopteran larvae were collected and analyzed for stable isotopes (δ15, δ13C) and United States Environmental Protection Agency (USEPA) Contaminants of Potential Concern (COPC) trace metals: V, Cr, Ni, Cu, Zn, As, Se, Sr, Hg, Pb, U, with a focus on Ni, U and Hg, in order to examine trace metal transport mobility within the lower trophic food web. Results from this study support intraspecific biomagnification of focal metals, with little evidence of interspecific biomagnification for Ni and U. Biofilms were ideal indicators for system contamination and Anuran larvae with the digestive tract removed gave a clear representation of the bioavailability of the focal metals. The importance of measuring baseline δ15N stable isotope data in lower trophic levels was displayed by Anuran larvae expressing unique δ15N signatures for each pond within the system. Although biofilms and detritus were high in both Ni and U concentrations, the levels observed in Anuran and Anisopteran larvae were lower indicating that only a portion of these contaminants are bioavailable. Hg concentrations increased through higher trophic levels indicating interspecific biomagnification. Transfer factors (TFs) from biofilm and detritus to higher trophic level organisms and hazard indexes (HQs) for Ni were low indicating little risk to those organisms. TFs for U were relatively low but displayed high HQs demonstrating reduced bioavailability but high risk due to the high U concentrations in this system. Hg TFs and HQs were both high in the Tims Branch tributary displaying a high risk for this trace metal and should be continued to be monitored closely. There still is risk to this ecosystem integrity as the COPC metals are being assimilated into lower trophic organisms.

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