oa Methane Ebullition from Labile and Refractory Lipidic Biomarkers from Sediment Traps in a Eutrophic Reservoir

Lipids biomarkers can be be useful to determine present and past temperature, microbial activity, biogeochemical cycles, rates or changes in the water column conditions. Refractory lipids, such as glycerol dialkyl glycerol tetraethers (GDGTs), can persist in sediments over long timescales and are commonly used as paleolimnological biomarkers. In contrast, phytoplankton-derived lipids tend to decompose faster, fueling higher methane production than those from terrestrial plants or animals. We performed a round year weekly monitoring of lipidic compounds, including GDGTs, fatty acids and polar compounds from sediment traps deployed in a eutrophic reservoir. We did not find a correlation between GDGTs or sterols with methane ebullition. By contrast, the shorter and more labile compounds, such as phytol and fatty acids, presented similar dynamics that methane ebullition. This difference indicates a preference of methanogenic archaea for these sedimentary lipids with more short chains and phytoplanktonic origin. and the low degradation of GDGTs. The present study highlights the variability in lipids sedimentation at the compound-specific level depending on its origin and structure with relevant consequences for the short-term degradation affecting methane ebullition and the long-term storage in sediments profiles being net carbon sinks.