Spatiotemporal distribution patterns of dissolved methane in lakes: How accurate are the current estimations of the diffusive flux path?

Lakes have been identified as an important source of atmospheric methane. Here the spatiotemporal distribution of dissolved methane was measured in a medium-sized freshwater lake. The data reveal that littoral zones (nearshore, shallow) are the predominant source of methane. Offshore-directed gradients of dissolved methane suggest the transport of methane from the nearshore zone to the pelagic epilimnion. The distribution patterns of epilimnetic methane were highly heterogeneous, independent of the mean lake-wide methane concentration. Consequently, the diffusive flux of methane to the atmosphere strongly varies with location in the lake. A comparison of the diffusive methane flux from different offshore sampling stations indicates that single-point measurements are not necessarily sufficient to estimate lake-wide emissions to the atmosphere accurately. Thus, spatially resolved measurements of methane emissions are needed to improve the reliability of estimates of the methane that lakes contribute to the global methane budget.