Evaluation of lipid biomarkers as indicators of changes in organic matter delivery to sediments from Lake Planina, a remote mountain lake in NW Slovenia

Lipid biomarker distributions were used to assess changes in organic matter delivery and preservation processes in recent sediments of Lake Planina, a remote eutrophic lake situated in the Julian Alps, NW Slovenia. Sterols and fatty acids are the most abundant lipids in the surface sediment layer. In deeper sediments, aliphatic alcohols and aliphatic hydrocarbons are relatively enriched, due to decreased susceptibility to degradation. Nearly 75% of contemporary bulk organic matter is of autochthonous origin, as suggested by low C/N values. Nevertheless, longer chain lipids, which are mainly of terrestrial origin, are more abundant than shorter chain lipids of mostly autochthonous origin in all the sediments. Thus, source assignment based on lipid composition is in a sharp disagreement with the origin of bulk organic matter. This bias is most probably introduced by selective degradation of lipids making them unreliable proxies for source apportionment in Lake Planina sediment.