Degassing fluxes in a temperate hydropower reservoir predictable by deep‐water dissolved oxygen but highly sensitive to discharge variability

Abstract Hydropower reservoirs contribute to methane (CH 4 ) and carbon dioxide (CO 2 ) emissions, like all aquatic ecosystems. Unique to hydropower reservoirs are degassing emissions that occur when deep‐water intakes move water with high CH 4 and CO 2 concentrations through turbines, leading to the release of these gases. However, few studies from hydropower reservoirs have measured seasonal variability and drivers of degassing fluxes, especially in temperate systems. We measured monthly degassing emissions in temperate Douglas Reservoir (Tennessee, USA) from 2023 to 2024. We found that degassing fluxes were highest in the summertime, and deep‐water CH 4 and CO 2 concentrations were predictable by deep‐water dissolved oxygen (DO) concentrations. Degassing emissions accounted for 37–62% of annually estimated CH 4 emissions, outweighing ebullitive emissions during summer months. We highlight the value of using DO data to estimate deep‐water CH 4 and CO 2 concentrations and degassing fluxes at higher temporal resolution to improve annualization and extrapolation of reservoir degassing emissions at broader scales.