METAL REMOVAL RATES FROM A DRINKING WATER RESERVOIR UNDERGOING OXYGENATION

Seasonal stratification of eutrophic lakes and reservoirs can result in low dissolved oxygen conditions in the hypolimnion (bottom waters). Low to no oxygen conditions can result in the reductive dissolution of minerals, such as Fe oxides and hydroxides, in sediment, releasing metals from sediments into the hypolimnion. Elevated concentrations of metals can have negative impacts on drinking water quality and human health. However, the release of metals can be controlled by hypolimnetic oxygenation (HOx) systems, which create well-oxygenated conditions in the hypolimnion, promoting oxidation and removal of metals. In this study, we calculated removal rates of barium (Ba), aluminum (Al), and calcium (Ca) from the water column of two freshwater drinking reservoirs: one with HOx and one without (control). To do this, we captured suspended sediment from the water column using sedimentation traps, then filtered and digested the suspended sediment matter using microwave digestion. We then calculated removal rates for Ba, Al, and Ca and compared them with removal rates of Fe and Mn. Removal rates varied among the metals and increased during oxygenation, altering the biogeochemical cycling patterns of these metals in comparison to the control reservoir. Ba removal rates were positively correlated with Fe, suggesting that Ba release and removal are controlled by Fe redox reactions. Al removal rates were associated with sediment input from tributaries. Ca removal rates are suspected to be the result of biological processes related to phytoplankton, but further studies need to be conducted to address this. Overall, our results suggest that oxygenation systems can enhance metal removal from freshwater drinking reservoirs, benefiting water quality and human health.