Impact of Reservoir Operation Policies on Spatiotemporal Dynamics of Sediment Methane Production and Release in a Large Reservoir

Reservoir operation policies affect sediment methane (CH₄) production and pathways through complex influence on hydrodynamic and biogeochemical processes in reservoir water and sediment. However, the underlying influencing mechanisms, especially the impact of operations on sediment CH₄ production and pathways, remain poorly understood. This study combines a physical-biogeochemical model with a reservoir operation model to evaluate operation impacts on spatiotemporal sediment CH₄ production and release dynamics and to analyze affiliated processes and driving factors. Three typical operation policies (i.e., standard, hedging, eco-friendly) are selected to create the operation scenarios, and a coupled physical-biogeochemical model is adopted to simulate and compare sediment CH₄ production, consumption, diffusion, and ebullition under these scenarios. The methods are applied in the second largest reservoir in China (i.e., Danjiangkou Reservoir) as a case study. Results show that annual total sediment CH₄ production among the scenarios ranges from 285.9 to 298.3 Gg C year⁻¹, while operation scenario outcomes significantly differ. Specifically, a significant CH₄ percentage (34%–39%) is oxidized in surface sediment while the remaining escapes sediment through diffusion and ebullition. Although diffusion accounts for >60% of the annual sediment CH₄ release, sediment ebullition ultimately dominates atmospheric CH₄ emissions. Annual total atmospheric CH₄ emissions range from 42.8 to 71.1 Gg C year⁻¹ and account for 14%–25% of the annual total sediment production among the three scenarios. The differences demonstrate that reservoir operations significantly impact CH₄ pathways and atmospheric emissions. This study provides implications for reservoir managers to coordinate socioeconomic and ecological protection while mitigating CH₄ emission targets.