Oxygenation and hydrologic controls on iron and manganese mass budgets in a drinking-water reservoir

Abstract

Munger ZW, Carey CC, Gerling AB, Doubek JP, Hamre KD, McClure RP, Schreiber ME. 2018. Oxygenation and hydrologic controls on iron and manganese mass budgets in a drinking-water reservoir. Lake Reserv Manage. 35:277–291. In seasonally stratified lakes and reservoirs, fluctuating hypolimnetic oxygen and hydrologic conditions in the watershed can influence the retention of metals and their exchange between the sediments and water column. In particular, iron (Fe) and manganese (Mn) cycling at the sediment–water interface can be dynamic in response to variability in the watershed and within the waterbody, which has substantial implications for drinking water quality. We calculated a mass budget for Fe and Mn in a shallow drinking-water reservoir over a 2-year period in which we manipulated the tributary inflow rate and dissolved oxygen (DO) concentrations in the hypolimnion at the reservoir scale. We found that the net Fe and Mn release from the sediments into the water column was suppressed during oxygenation; however, both metals continued to be released from the sediments, even during well-oxygenated conditions. Oxygenation in the hypolimnion had no effect on the net export of metals from the reservoir to downstream. Instead, the overall net export of Fe and Mn during the stratified period was influenced by hydrologic inflows. In summary, we found that manipulating hypolimnetic oxygenation had an important effect on the cycling of Fe and Mn within the hypolimnion, but that the net retention of metals in the reservoir was driven primarily by hydrology.