Lipid Biomarkers and Their Stable Carbon Isotopes in Oxic and Anoxic Sediments of Lake Bled (NW Slovenia)

Sources of lipid biomarkers in two Lake Bled sediment cores deposited under oxic (Zaka Bay) and anoxic (WB) conditions were determined using stable carbon isotopes. Lipid biomarkers were of autochthonous origin mainly from planktonic and microbial sources. δ¹³C values for long-chain (LC) <i>n</i>-alkanes, short-chain (SC) and LC <i>n</i>-alcohols, SC <i>n</i>-fatty acids (FAs) were similar for both sediments, showing that identification of their sources was not related to different depositional regimes. A larger contribution of more refractory terrestrial organic matter (OM) was observed in δ¹³C values obtained from SC <i>n</i>-FAs in both environments and from SC <i>n</i>-alkanes in Zaka Bay. In contrast, the δ¹³C values observed in LC <i>n</i>-FAs, and especially in sterols, were lower in the WB than in Zaka Bay, indicating the pronounced contribution of an anaerobic, bacterial origin. Overall, the data indicated that the main source of lipids was autochthonous in both sediment environments including, LC <i>n</i>-alkanes, <i>n</i>-alcohols, <i>n</i>-FAs and C₂₉ sterols previously assigned to an allochthonous higher plant source. It further follows that isotope geochemistry gives an additional information for source assignment in aquatic systems.