Sources of organic matter for bacteria in sediments of Lake Rotsee, Switzerland
Determination of carbon sources and microbial activity in lake sediment is important for understanding organic carbon preservation and methane production. This study aimed to determine the organic carbon sources and microbial activity over the last 140 years in sediments of methanotrophic Lake Rotsee (Switzerland). We investigated phospholipid-derived fatty acid biomarkers and their stable carbon isotope signatures in the sediments of this eutrophic lake. Strong bacterial activity in the sediment deposited during the 1920s–1960s could account for the relatively low ratio of long-chain to short-chain fatty acid ((C24 + C26 + C28)/(C14 + C16 + C18), TARFA) values, which is consistent with low TOC/TN ratios in the sediment deposited during that interval. The carbon stable isotope records, both bulk and compound-specific, showed greater values at such times, although the offset between the bulk and fatty acids decreased. This implies that the microbial community residing at sediment depths deposited in the 1960s preferentially utilised the compounds derived from the enhanced surface-water productivity at that time. This observation contrasts with data from the depth intervals before and after, when a major portion of the labile organic matter was derived from methane-sourced production. In sediments deposited before ca. 1964, the overall very low fatty acid δ13C values suggest that labile carbon was primarily derived from methanotrophs.
KeywordsBiomarker Phospholipid fatty acids Stable isotopic analysis Methanotrophs
We acknowledge Dr. Carsten J. Schubert for making field work possible, Dr. Johan W.H. Weijers for help with PLFA extraction and analysis, and Dr. Klaas G.J. Nierop (Utrecht University) for helpful discussions on fatty acids. Arnold van Dijk, Dominika Kasjaniuk, Michiel Kienhuis and Linda van Roij (Utrecht University) all provided technical and analytical assistance. The National Science Foundation of China (Nos. 31370478 and 31670461) and the Netherlands Organization for Scientific Research (NWO) Earth and Life Sciences (No. 820.02.017) supported this research.
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