Human-Dominated Land Use Preferentially Amplifies Global Riverine Methane Ebullition: New Insights into Estimation and Mitigation Efforts.

River systems are significant methane (CH4) sources, with ebullition representing an important but highly uncertain emission pathway. Although land use is known to influence aquatic CH4 emissions, the mechanisms by which land use types regulate ebullition remain poorly understood at broad scales. Here, by combining a five-year field survey of China's major rivers with a global data set, we revealed a strong land-use-dependent pattern in riverine ebullition globally. Rivers draining human-dominated urban and agricultural landscapes exhibited ebullitive fluxes over four times higher than those in relatively natural (i.e., forested or grassland) basins, with ebullition contributing >59% of CH4 emissions in human-dominated systems compared to <46% in natural ones. This is mainly linked to the land-use-induced changes in aquatic conditions, including nutrient enrichment, labile organic carbon inputs, oxygen depletion, and fine sediment accumulation, which collectively promote methanogenesis and bubble formation. Upscaling estimates for human-dominated regions indicated a 44% increase in riverine CH4 emissions from 1960 to 2020 due to agricultural and urban expansion, with ebullition responsible for 76% of this rise. Conventional upscaling methods that ignore land-use effects would introduce biases exceeding 20% in ebullition estimates. Implementing watershed-scale restoration and targeting ebullition mitigation in human-dominated systems presents a critical opportunity for reducing aquatic CH4 emissions. Our findings advance understanding of land-use controls on riverine CH4 ebullition and provide science-based guidance for upscaling frameworks and developing targeted management.