Reservoir sedimentation and storage increases availability of potentially toxic elements from historic Pb-Zn-F mining contamination.

Pseudo-total and sequential extraction analyses of stream sediment and reservoir bottom samples with calculated pollution indices were used to investigate the efficacy of reservoir sedimentation and the effects of impoundment on recent fluorspar mineral processing wastes and legacy contaminants from historic Pb-Zn mining. Contamination levels showed little natural attenuation over three decades since mining ceased. While the reservoir acts as a partially effective trap for Pb, with decreasing levels found in bottom sediments further away from the entry point for suspended river sediment, elevated Zn concentrations occur throughout, with Mn concentrated distally
in deeper water sediments nearest to the abstraction and discharge points. As the majority of Cd, Mn and Zn in the reservoir sediments are found in the exchangeable fraction, the net result is a store of fine-grained, chemically and biologically available contamination, which is readily amenable to disturbance and redispersion through operational or meteorological effects, which in turn may potentially be compounded by future climate change.