Sources of Lipids in Anoxic Lacustrine Sediments Using Stable Carbon Isotopes

The origin of organic matter in recent anoxic sediments of the alpine Lake Bled (NW Slovenia) was determined by analyzing the carbon isotope composition of lipid biomarkers, i.e. alkanes, alcohols, sterols and fatty acids, busing compound specific, carbon isotope analysis. The results indicate that, although biomarker analysis indicated mostly plankton and terrestrial sources for lipids, an important part of sedimentary lipids, especially sterols, are autochthonous, of anaerobic microbial (methanotrophic) origin. Marked differences were observed in delta C-13 values of lipid biomarkers in settling particles collected 2 m above the bottom, and in delta C-13 values determined in surface sediment. These results indicate that even some compounds found in both particulate organic matter and sediments are the same in terms of chemical structures, their sources can be different and thus, isotopic composition should be used as a complementary tool for source identification.