High Spatio-Temporal Dynamics of Methane Production and Emission in Oxic Surface Water

The discovery of methane (CH4) accumulation in oxic marine and limnic waters led to redefine the role of aquatic environments in the regional CH4 cycle. Although CH4 accumulation in oxic surface waters became apparent over recent years, the sources are still subject to controversial discussions. We present high-resolution in situ measurements of CH4 concentration and its stable isotope composition in a stratified oligo-mesotrophic lake. We show that CH4 accumulation in surface waters originates from a highly dynamic interplay between (oxic) CH4 production and emission to the atmosphere. Laboratory incubations of different phytoplankton types and application of stable isotope techniques provide the first unambiguous evidence that major phytoplankton classes in Lake Stechlin per se produce CH4 under oxic conditions. Combined field and lab results show that the photoautotrophic community is an important driver for CH4 production and its highly dynamic accumulation in oxic surface waters.