Sedimentation of autochthonous labile lipids facilitates methane ebullition

Methane (CH₄) emissions from reservoirs contribute largely to global greenhouse gas budgets, with ebullition from sediments being the main pathway. Methanogenesis is the final step in the anaerobic microbial degradation of organic matter, but the specific substrates promoting this step still remain poorly understood. Here, we identify specific lipids in the organic matter from sediment traps during a one-year cycle to further relate them with in-situ CH₄ ebullition measurements. Phytol, short-chain n-alkanols, and short-chain fatty acids showed either a strong synchrony or a brief one-week delay to CH₄ ebullition peaks, indicating a fast transformation of these substrates by syntrophic microorganisms into precursors of methanogenesis. Phytol sedimentation was strongly coupled to CH₄ ebullition, highlighting the importance of this chlorophyll degradation substrate. Also, sedimentation of unsaturated fatty acids from autochthonous algae and zooplankton was synchronized with CH4 ebullition. Our research underlines the role of lipid structure, origin, and seasonality, providing key insights for predicting CH4 ebullition under the current increase in eutrophication.