Strong CH4 emissions modulated by hydrology and bed sediment properties in Qinghai-Tibetan Plateau rivers

•CH4 flux in silty rivers was 13–14 times that in sandy or gravel rivers.•Sediment silt% and bed sediment properties explained 76% of the CH4 flux.•Fine sediments promote benthic OC availability and reducing redox conditions.•Fine sediments allow for a denser colonization of CH4-producing microbes.•Grain size serves as an integral proxy for favorable conditions of CH4 production. Fluvial systems evade massive amounts of greenhouse gases to the atmosphere where stream hydrology and riverbed biogeochemistry imposes important in situ controls. Current paradigm however lacks an effective framework to account for this effect. Here, we investigated CH4 and CO2 emissions from 28 rivers on the Qinghai-Tibetan Plateau, an area of strong fluvial emissions and high climate sensitivity. We found two orders of magnitude higher CH4 fluxes in silt-dominated (the finest riverbed sediment type) than in sand- or gravel-dominated rivers (1,200 ± 1,290 vs 88 ± 83 and 93 ± 77 μmol m−2 d−1; p