Hydrologic and environmental drivers of metals (Al, Ba, Cu, Sr) in two drinking water reservoirs in southwestern Virginia

Abstract

Contamination of drinking water supplies poses a growing challenge for drinking water utilities due to treatment cost and changing climatic conditions. In this study, I examined the drivers of four metals—aluminum (Al), barium (Ba), copper (Cu), and strontium (Sr)—across two drinking water reservoirs in southwestern Virginia over four years. One of the reservoirs has a hypolimnetic oxygenation system; the other does not and serves as a control. Using datasets of metal concentrations and other water quality measurements in the water column, suspended sediment and reservoir inflow, in addition to hydrologic measurements of precipitation and inflow discharge, I used time series modeling and multivariate analyses to assess the relative roles of hydrologic and geochemical processes driving metal behaviors in the two reservoirs. Results show that Al concentrations were primarily influenced by high-flow events, consistent with mobilization of clays from erosion (physical weathering) during rainfall. In contrast, Ba and Cu showed stronger sensitivity to oxidation-reduction conditions, with elevated concentrations under reducing conditions and reduced levels in response to oxygenation, likely due to sorption of these metals onto iron and manganese oxides, which are released to the water column under reducing conditions. Strontium displayed intermediate behavior, showing signatures of oxidation-reduction and pH-driven desorption processes, in addition to dilution during high discharge events. For all four metals, patterns varied by year, highlighting the importance of long-term monitoring to capture both seasonal trends and event-driven variability. Our findings highlight the need for integrated observational and modeling approaches to delineate metal dynamics in reservoir systems and inform strategies for maintaining safe drinking water under changing environmental conditions.