Reservoir methane emission response to varying organic carbon loads under multiple socioeconomic development scenarios

Reservoirs are riverine organic carbon (OC) retention and methane (CH₄) emission hotspots. However, the response of reservoir CH₄ cycling processes and emissions to varying OC loads under different socioeconomic development scenarios remains unclear. Accordingly, this study evaluates the impact of OC loads on reservoir CH₄ cycling processes and predicts future emissions under multiple socioeconomic development scenarios. A coupled physical-biogeochemical reservoir model was used to simulate CH₄ production, oxidation, diffusion, and ebullition dynamics. Three socioeconomic development scenarios (i.e., low, steady, and high-speed development) were adopted to project riverine OC loads and reservoir CH₄ emission. Using the second largest reservoir in China (i.e., Danjiangkou Reservoir) as a case study, the results demonstrate that increased OC loads led to a reduction in sediment CH₄ oxidation efficiency. As OC loads increased, the dominant sediment CH₄ release pathway shifted from diffusion to ebullition. A linear relationship was also observed between CH₄ ebullition and OC loads, while CH₄ diffusion exhibited a nonlinear growth trend. The findings highlight the importance of OC loads in regulating reservoir CH₄ cycling. Furthermore, CH₄ emissions may significantly increase (34 %–125 %) by 2050, raising emission control concerns. This study provides a modelling tool and fresh implications for future reservoir emission estimations and watershed management in the pursuance of carbon (C) neutrality goals.