Spatio-temporal variations of methane fluxes in sediments of a deep stratified temperate lake

Summary: Spatio-temporal variability of sediment-mediated methane (CH4) production in freshwater lakes causes large uncertainties in predicting global lake CH4 emissions under different climate change and eutrophication scenarios. We conducted extensive sediment incubation experiments to investigate CH4 fluxes in Lake Stechlin, a deep, stratified temperate lake. Our results show contrasting spatial patterns in CH4 fluxes between littoral and profundal sites. The littoral sediments, ∼33% of the total sediment surface area, contributed ∼86.9% of the annual CH4 flux at the sediment-water interface. Together with sediment organic carbon quality, seasonal stratification is responsible for the striking spatial difference in sediment CH4 production between littoral and profundal zones owing to more sensitive CH4 production than oxidation to warming. While profundal sediments produce a relatively small amount of CH4, its production increases markedly as anoxia spreads in late summer. Our measurements indicate that future lake CH4 emissions will increase due to climate warming and concomitant hypoxia/anoxia.