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.