Lakes have been identified as an important source of atmospheric methane. However, methane dynamics and internal pathways in lakes are not yet clear. In the littoral zone of lakes sediment temperatures are comparatively high supporting high methane production rates. Furthermore, littoral sediments are intensively disturbed by surface and internal waves which triggers and enhances the release of methane from the sediments. Thus, lake littoral zones may play a central role for the lake-wide methane emissions. This hypothesis will be tested by investigating the dynamics of methane release from littoral sediments, the diffusive and advective transport and the distribution of dissolved methane within the water body, and the lake-wide methane fluxes to the atmosphere. From the quantification of these processes the relative contribution of methane from the littoral zone to the lake-wide methane emissions can be estimated. In Lake Constance, extensive field experiments will be conducted covering a broad range of spatial and temporal scales. A special focus will be on the spatio-temporal distribution patterns, the transport processes, and the exchange of dissolved methane between the littoral zone and the open water body. These experiments will be complemented by numerical simulations of the methane dynamics conducted with a 3D hydrodynamic model that is coupled to an aquatic ecosystem model. The purpose of the numerical simulations is the estimation of lake-wide, annual emissions of dissolved methane to the atmosphere under changing boundary conditions.
