Increased sediment oxygen flux in lakes and reservoirs: The impact of hypolimnetic oxygenation

Hypolimnetic oxygenation is an increasingly common lake management strategy for mitigating hypoxia/anoxia and associated deleterious effects on water quality. A common effect of oxygenation is increased oxygen consumption in the hypolimnion and predicting the magnitude of this increase is the crux of effective oxygenation system design. Simultaneous measurements of sediment oxygen flux (J_O2) and turbulence in the bottom boundary layer of two oxygenated lakes were used to investigate the impact of oxygenation on J_O2. Oxygenation increased J_O2 in both lakes by increasing the bulk oxygen concentration, which in turn steepens the diffusive gradient across the diffusive boundary layer. At high flow rates, the diffusive boundary layer thickness decreased as well. A transect along one of the lakes showed J_O2 to be spatially quite variable, with near-field and far-field J_O2 differing by a factor of 4. Using these in situ measurements, physical models of interfacial flux were compared to microprofile-derived J_O2 to determine which models adequately predict J_O2 in oxygenated lakes. Models based on friction velocity, turbulence dissipation rate, and the integral scale of turbulence agreed with microprofile-derived J_O2 in both lakes. These models could potentially be used to predict oxygenation-induced oxygen flux and improve oxygenation system design methods for a broad range of reservoir systems.