TRACE METAL CONCENTRATIONS AND SPECIATION WITHIN SEDIMENT OF THE UPPER LITTLE TENNESSEE RIVER BASIN

The Upper Little Tennessee River (LTR) possesses one of the most diverse assemblages of biota in North America, including more than 40 species of aquatic organisms that are considered rare at some level. Two of importance are the endangered Appalachian elktoe mussel (Alasmidonta raveneliana) and the threatened spotfin chub (Erimonax monachus), both of which declined significantly following hurricanes Frances and Ivan in 2004. Although the cause(s) of decline have yet to be determined, management agencies have questioned whether the changes in populations are related to the influx or remobilization of sediment and/or contaminants that they carry (including trace metals). The intent this study was to provide a preliminary assessment of the potential impact of trace metals from water and sediment on elktoe mussels, and determine the source of trace metals to the aquatic system between Lake Emory and Fontana Lake. Analyses of sediment samples from Lake Emory and the Upper LTR show that Cu, Ni, Zn and Cd concentrations locally exceed probable effect guidelines for aquatic biota. The highest concentrations of trace metals are associated with fine-grained (silt- and clay-sized) sediments. Sequential extraction analyses show that nearly all of the Ni is associated with the exchangeable fraction and, thus, is likely to be bioavailable. However, approximately 50 % or more of the Cu, Cd, and Zn is associated with the residual sediment phase. These data, combined with spatial trends in metal concentrations, ²¹⁰Pb analyses of sediment cores, and modeling using a new sediment mixing routine of tributary contributions suggest (1) that most of the metal are not readily available to biota for accumulation, and (2) that the trace metals are primarily derived from bedrock units enriched in sulfide minerals. 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.