Methane accumulation and its potential precursor compounds in the oxic surface water layer of two contrasting stratified lakes
2 Faculty of Geography, Yunnan Normal University, China
3 Department of Environmental Sciences, University of Basel, Switzerland
4 Department of Plankton and Microbial Ecology, Leibniz Institute of Freshwater Ecology and Inland Fisheries Stechlin, Germany
O 4.4 in Environment and Pollution
28.09.2023, 16:15-16:30, H 36
Oversaturation of methane (CH4) in oxygenated waters is a widespread phenomenon, challenging the traditional perception of strict anoxic methanogenesis. Recent findings have uncovered mechanisms that produce CH4 in oxic environments. While some processes contributing to the accumulation of CH4 in the oxygenated water layers of lakes have been identified, temporal variations and their drivers are still poorly understood. In this study, we investigated the accumulation of CH4 in oxic water layers of two contrasting lakes: Lake Willersinnweiher (shallow, eutrophic) and Lake Stechlin (deep, mesotrophic) from 2019 to 2020. Strong CH4 oversaturation was observed in the surface waters of both lakes, primarily concentrated around the thermocline. In both lakes, increases in CH4 concentrations from the surface to the thermocline were mostly associated with an enrichment in 13C-CH4 and 2H-CH4, indicating a complex interaction of multiple processes, such as CH4 oxidation, CH4 transport from littoral sediments, and oxic CH4 production, sustaining and regulating CH4 oversaturation. Moreover, incubation experiments with 13C- and 2H-labelled methylated P-, N-, and C- compounds clearly demonstrated that methylphosphonate, methylamine, and methionine acted as precursors of CH4 and partially sustained CH4 oversaturation. This highlights the need to better understand the mechanisms underlying CH4 accumulation by focusing on production and transport pathways of CH4 and its precursor compounds.
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