Microbial Community Abundance Affects the Methane Ebullition Flux in Dahejia Reservoir of the Yellow River in the Warm Season

Reservoirs are an integral part of the global carbon cycle and generally considered to be methane (CH4) emission hot spots. Although remarkable research achievements have been made concerning CH4 ebullition from inland waters, such as rivers, lakes, and ponds, few have been devoted to CH4 ebullition from plateau reservoirs. The present study focused on CH4 ebullition from the Dahejia Reservoir located in the upper reaches of the Yellow River. We analyzed the spatial and temporal characteristics of CH4 ebullition flux across the water-atmosphere interface between July and August 2021. We also evaluated the influence of microbes on CH4 ebullition flux. The results showed that (1) CH4 ebullition was the dominant mode of CH4 emissions in the study site, which contributed to 78.85 ± 20% of total CH4 flux. (2) The mean CH4 ebullition flux in the nighttime (0.34 ± 0.21 mg m−2 h−1) was significantly higher than that in the daytime (0.19 ± 0.21 mg m−2 h−1). The mean CH4 ebullition flux first decreased and then increased from the upstream (0.52 ± 0.57 mg m−2 h−1) to the downstream (0.43 ± 0.3 mg m−2 h−1) of the Yellow River. (3) Sediment microbes affected the CH4 ebullition flux primarily by changing the microbial community abundance. The regression analysis showed that CH4 ebullition flux had a significantly linear negative correlation with microbial abundance in sediments. The redundancy analysis further showed CH4 ebullition flux was significantly positively correlated with the abundances of Firmicutes and Actinobacteria, and negatively with that of Proteobacteria and Chloroflexi. Among abiotic variables, CH4 ebullition flux was closely related to total phosphorus, total organic carbon, pH and nitrate nitrogen