Contrasting methane emissions from upstream and downstream rivers and their associated subtropical reservoir in...

Subtropical reservoirs are an important source of atmospheric methane (CH₄). This study investigated the spatiotemporal variability of bubble and diffusive CH₄ emissions from a subtropical reservoir, including its upstream and downstream rivers, in eastern China. There was no obvious seasonal variation in CH₄ emissions from the main reservoir, which increased slightly from the first half year to the next half year. In the upstream river, CH₄ emissions were low from February to June and fluctuated widely from July to January due to bubble activity. In the downstream river, CH₄ emissions were lowest in February, which was possibly influenced by the low streamflow rate from the reservoir (275 m³ s^-1) and a short period of mixing. There was spatial variability in CH₄ emissions, where fluxes were highest from the upstream river (3.65 ± 3.24 mg CH₄ m^-2 h^-1) and lowest from the main reservoir (0.082 ± 0.061 mg CH₄ m^-2 h^-1), and emissions from the downstream river were 0.49 ± 0.20 mg CH₄ m^-2 h^-1. Inflow rivers are hot spots in bubble CH₄ emissions that should be examined using field-sampling strategies. This study will improve the accuracy of current and future estimations of CH₄ emissions from hydroelectric systems and will help guide mitigation strategies for greenhouse gas emissions.