Methane release through resuspension of littoral sediment

Sediment in the littoral zone of lakes is frequently disturbed by wave action or bioturbation, resulting in sediment resuspension. In undisturbed sediment, methanotrophic bacteria efficiently reduce the diffusive flux of methane into the water column. In a microcosm study, the resuspension of littoral sediment was simulated in sediment cores for a winter (n = 3) and a summer situation (n = 3). The erosion of surface sediment resulted in a large flux of methane into the overlying water (207 +/- 176 mu mol h(-1) m(-2) in winter and 73 +/- 18 mu mol h(-1) m(-2) in summer). Only a minor part (16 +/- 7%) of the methane released was oxidized by methanotrophic bacteria, whereas the major part escaped into the water column. Only 6-16% of the littoral zone has to be resuspended to reach the same flux as from undisturbed littoral sediment. For the daily flux, a sediment resuspension has to last 1-4 h to reach the undisturbed daily flux. The study reveals the important role of sediment resuspension in the littoral methane cycle as an intense but variable source of methane of largely unknown magnitude.