TRACE METAL TRANSPORT AND PROVENANCE WITH THE UPPER LITTLE TENNESSEE RIVER BASIN, NORTH CAROLINA

The Upper Little Tennessee River possesses one of the most diverse assemblages of aquatic biota in North America, including the endangered Appalachian elktoe mussel (Alasmidonta raveneliana). For unknown reasons, the elktoe mussel declined significantly following hurricanes Frances and Ivan in 2004. The primary intent of this study was to determine the potential impact of trace metals from non-point sources on elktoe mussels and other aquatic biota located between Lake Emory and Fontana Lake. Cu, Ni, Zn and Cd concentrations in reservoir and channel bed sediments locally exceed probable effect guidelines for aquatic biota. The highest concentrations of trace metals are associated with fine-grained (silt- and clay-sized) sediments. Thus, total trace metal concentrations within the water column tend to increase during flood events, and often exceed toxicity guidelines. However, sequential extraction analyses suggest that approximately 50 % or more of the Cu, Cd, and Zn are associated with the residual sediment phase, significantly reducing their bioavailability. Ni is primarily associated with the exchangeable phase, and is therefore more bioavailable. The extraction data, combined with spatial trends in metal concentrations, ²¹⁰Pb analyses of sediment cores from Lake Emory, and the mass balance modeling of tributary inputs of sediment and trace metals to the axial drainage suggest that most of the metals are derived from sulfide minerals contained within the underlying bedrock. Depth trends in Cu concentrations within cores from Lake Emory indicate, however, that Cu loadings to the river have increased through time and may also be derived from locally used pesticides. In addition, the geochemically based, mass balance modeling results show that metal loadings are closely related to land-use activities and basin degradation within tributary catchments. The link presumably results from the increased erosion of saprolitic sediments characterized by relatively high trace metal concentrations.