Inland waters have been estimated to be the largest source of atmospheric methane (CH4) at the global scale. Manmade reservoirs are particularly strong emitters globally, with river impoundments in the temperate zone being among the global hotspots of CH4 emissions from freshwater aquatic systems. I will present and analyze extensive measurements of CH4 production and emission rates in river impoundments and compare fluxes and drivers of emissions from these systems with those from more natural rivers and lakes. The results show that sediment management is key to potential mitigation efforts aimed at reducing greenhouse gas emissions from river impoundments. I will also present results from a first attempt to harvest CH4 from sediments during sediment management measures in reservoirs.
High CH4 emission rates are mainly sustained by ebullition, i.e., bubble-mediated transport from the sediment to the atmosphere. I will summarize recent efforts in understanding gas bubble formation and release from aquatic sediments and in quantifying the amount of gas that is stored in sediments. This research is crucial for improving mechanistic models of CH4 dynamics in aquatic ecosystems and for assessing dynamic, site-specific CH4 budgets.