Spatial methane pattern in a deep freshwater lake: Relation to water depth and topography

Freshwater lakes are regarded as important methane (CH4) sources, accounting for similar to 20% of natural emission. To improve the assessment of the global greenhouse effect, it is necessary to consider spatial variability within lakes. Here, CH4 concentrations in the water column and sediment layers, as well as the sediment CH4 production potentials and diffusive fluxes, were studied in the littoral, intermediate, and profundal zones of the medium-sized (425 ha), deep (maximum depth 69.5 m) Lake Stechlin (Germany). Sediment CH4 concentrations, production potentials and sediment-water interface diffusive fluxes showed significant spatial heterogeneity and were highest in the profundal zone. CH4 concentrations in the surface water did not differ among the studied locations, indicating a decoupling from the production sites in the sediment. The high amount of CH4 in profundal sediments that might potentially be released to the atmosphere is either trapped or oxidized within the water column, while the surface water dissolved CH4 is more related to the dynamics in the epilimnion. The divergence in sediment physical (water content, grain size) and chemical (organic matter quantity or quality, sulfate) properties across the lake leads to variations in CH4 dynamics which are restricted to deeper habitats in this type of lake. (C) 2020 Elsevier B.V. All rights reserved.