Deciphering CH4 and CO2 emissions from an alpine reservoir: spatiotemporal patterns and underlying mechanisms

Alpine reservoirs are a key but poorly quantified source of greenhouse gas (GHG) emissions in inland waters. This study investigated the spatio-temporal variations and driving factors of methane (CH4) and carbon dioxide (CO2) fluxes at the Liujiaxia (LJX) Reservoir (1,735 meters above sea level), a high-altitude hydropower system in the upper reaches of the Yellow River, through multi-season field activities (2021-2023). High-frequency flux measurement, stable isotope analysis (δ13C-CH4 and δ13C-CO2), and statistical modeling determined the distinct emission patterns between the central area and the nearshore area. This dataset contains the data of reservoir CH4 and CO2 fluxes obtained at different sampling points at different times, as well as the corresponding environmental factor data. We found that the CH4 is mainly released through ebullition. Especially in summer, the emissions are 5.7 times higher than those in spring or winter. Isotope analysis indicates that the methane production processes in the central region and the nearshore region are different. Water management has increased emissions upstream, where methane and CO₂ fluxes are 3.7 times and 1.8 times those downstream respectively. Using the random forest model, we estimate that the annual methane emissions are 0.23 Gg and the carbon dioxide emissions are 20.18 Gg. These findings reveal how water management and natural processes drive greenhouse gas emissions from alpine reservoirs, providing valuable insights for global emissions models.