The small diffusive fluxes tend to suggest that CH4 emission from the sediments is low.
However in Lake Wohlen, the fact that gas bubblescan be observed at the surface, as well as the high CH4 concentration in water (364-1,718 nmol L-1compare to saturated concentration in surface water of ~3 nmol L-1) suggest another pathway of CH4 emission. At short OET, the organic matter is rapidly transferred to the methanogenic sediment layersresulting in the build-up of relatively high CH4 concentration. As high CH4
concentration is the prerequisite for ebullition, OET may be one important regulator of CH4 ebullition from lake sediments. The preliminary result from Del Sontro et al.(unpublished data) indicated high ebullition CH4flux (120-160 gC m-2yr-1) in Lake Wohlen. Therefore, OET seems to trigger high CH4 production in Lake Wohlen.