The effects of hypolimnetic oxygenation on the chemical, physical, and biological properties of a shallow drinking water reservoir

Hypolimnetic anoxia can result in higher internal phosphorus (P) loads from the sediments to the water column, thereby increasing nutrient availability, making preventing anoxia a major goal for lake managers to improve water quality. Side-stream saturation (SSS), a type of hypolimnetic oxygenation system, has been developed to maintain oxygenated conditions at the sediments by withdrawing oxygen-depleted water from the hypolimnion to an on-site facility and injecting it with oxygen under high pressure before returning it to the hypolimnion. While this technique has been studied in select water bodies, to date it has not been successfully deployed in a shallow lake. This study investigated the effects of an SSS system deployed at Falling Creek Reservoir, a shallow drinking water reservoir located in Vinton, Virginia, USA. Specifically, we examined the effects of the SSS system on several chemical, physical, and biological response variables to ascertain the short-term impacts of hypolimnetic oxygenation on reservoir water quality. We found that the SSS system was successful in increasing dissolved oxygen concentrations in the reservoir hypolimnion without weakening stratification, warming the sediments, or increasing turbidity; however, we were unable to detect any short-term effects of SSS operation on P concentrations, P loading, pH, chlorophyll a, or algal density. Interestingly, we also observed an increase in oxygen demand in response to SSS operation, which must be taken into account when deploying oxygenation systems in the future. Continued monitoring is necessary to more completely assess the long-term impacts of SSS operation on water quality at Falling Creek Reservoir.