GRL dataset

Lakes and reservoirs are significant sources of methane (CH4) and carbon dioxide (CO2) in global scale, yet their responses to climate change remain inadequately studied.We present high-resolution vertical profiles of CH4 and CO2 concentrations to elucidate their production, storage, and emission dynamics in a eutrophic subtropical reservoir. Methanogenesis initiated in the hypoxic hypolimnion led to a steady rise in CH4 and CO2 levels, with CH4 comprising up to ~50% of total carbonaceous greenhouse gases during ventilation. During stratification, oxic CH4 production dominated in surface waters, while vertical mixing, driven by cooling and wind events, enhanced hypolimnetic CH4 release. A synthesis of global CH4 fluxes and stratification days suggests that prolonged stratification may enhance CH4 storage but limit its release from bottom waters. With increasing eutrophication and global warming, enhanced stratification could amplify the climatic impact of aerobic, rather than anaerobic, CH4 production in subtropical lakes and reservoirs.