Oxygen Dependent Temperature Regulation of Benthic Fluxes in Reservoirs

Temperature and dissolved oxygen concentration are critical factors affecting the exchange of solutes between sediment and water; both factors will be affected by warming of lakes and thereby influence water quality. Temperature and oxygen responses of single solute fluxes are well known; however, not much is known about the interaction of temperature and oxygen in regulating the balance of different fluxes in the benthic environment. We analyzed benthic flux (mobilization and immobilization) data of various solutes (dissolved organic carbon (DOC), CH4, NO3−‐N, NH4+‐N, SRP, SO4−, Fe, Mn, and O2) collected from laboratory incubations of 142 sediment cores from 5 different reservoirs incubated under varying in situ temperature and oxygen conditions. Oxygen was the primary driver of benthic fluxes, while temperature and total organic content were secondary. Temperature effects on benthic fluxes were stronger under anoxic conditions which imply that warming will substantially increase the benthic fluxes if the sediment surface becomes anoxic. The varying temperature response of processes underlying the studied fluxes will result in a shift of their relative importance in the benthic environment, especially in shallow lakes that are more vulnerable to warming. For example, more anoxic conditions will shift the equilibrium between net sulfate reduction and methane release toward the latter. We also predict that physical effects of warming leading to hypolimnetic oxygen depletion, that is, stronger stratification and longer hypolimnetic confinement will increase the benthic mobilization of phosphorus, DOC, and methane into water and immobilization of sulfate by the sediments even in deep lakes. Plain Language Summary Temperature and dissolved oxygen concentration control the release of undesirable components buried in lake or reservoir sediments, that is, nutrients, metals, and organic matter, which can cause water quality problems. We investigated the effects of rising temperature and levels of oxygen on the release of undesirable components by performing experiments using sediments and water from five different reservoirs. The sediments with a layer of water on top were incubated under different in situ temperature (low and high) and oxygen conditions (with and without). Our results show that the absence of oxygen was the main cause of the release of nutrients and metals. When there was no oxygen in the sediment and water, nutrients and metals were released fro