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

Subtropical reservoirs are an important source of atmospheric methane (CH(4)). This study investigated the spatiotemporal variability of bubble and diffusive CH(4) emissions from a subtropical reservoir, including its upstream and downstream rivers, in eastern China. There was no obvious seasonal variation in CH(4) emissions from the main reservoir, which increased slightly from the first half year to the next half year. In the upstream river, CH(4) emissions were low from February to June and fluctuated widely from July to January due to bubble activity. In the downstream river, CH(4) emissions were lowest in February, which was possibly influenced by the low streamflow rate from the reservoir (275 m(3) s(−1)) and a short period of mixing. There was spatial variability in CH(4) emissions, where fluxes were highest from the upstream river (3.65 ± 3.24 mg CH(4) m(−2) h(−1)) and lowest from the main reservoir (0.082 ± 0.061 mg CH(4) m(−2) h(−1)), and emissions from the downstream river were 0.49 ± 0.20 mg CH(4) m(−2) h(−1). Inflow rivers are hot spots in bubble CH(4) emissions that should be examined using field-sampling strategies. This study will improve the accuracy of current and future estimations of CH(4) emissions from hydroelectric systems and will help guide mitigation strategies for greenhouse gas emissions.