Concentrations, Sources, and Potential Ecological Impacts of Selected Trace Metals on Aquatic Biota within the Little Tennessee River Basin, North Carolina

The Upper Little Tennessee River (ULTR) possesses one of the most diverse assemblages of aquatic biota in North America, including the endangered Appalachian elktoe mussel (Alasmidonta raveneliana). Populations of the Appalachian elktoe declined significantly following a 2004 flood generated by hurricanes Frances and Ivan. Although the cause(s) of decline have yet to be determined, population declines may reflect exposure to contaminated sediment within the river system. The objectives of this study were to provide a preliminary assessment of the potential impact of sediment-associated trace metals on aquatic biota, particularly the Appalachian elktoe mussel, and to determine the source(s) of trace metals to the axial channel. Total sediment-associated Cu, Cr, Ni, and Zn concentrations within the ULTR locally exceeded threshold and probable effect guidelines for aquatic biota. These data are consistent with previous analyses that found particulate and dissolved concentrations of Cu in river waters periodically exceeded aquatic impact guidelines. However, the data conflict with (1) metal speciation analyses that show that Cu, Cr, and Zn are largely associated with the residual, non-available sediment phase, and (2) trace metal concentrations that are higher in mussel shells from the Tuckasegee River, a control site with intact populations, than in the ULTR. Moreover, the analyses suggest that most of the metals are derived from sulfide minerals contained within the underlying bedrock and, in the case of Cu, from locally used pesticides. The importance of the underlying bedrock as a significant long-term trace metal source suggests that Appalachian elktoe mussels were exposed to high levels of Cu, Cr, Ni, and Zn both before and after the 2004 event. Thus, it appears unlikely that the decline of Appalachian elktoe populations is related primarily to trace metals.