Vertical distributions of bound saturated fatty acids and compound-specific stable carbon isotope compositions in sediments of two lakes in China: implication for the influence of eutrophication.

Lakes Dianchi (DC) and Bosten (BST) were determined to be at different stages of eutrophication, by use of total organic carbon content, bulk carbon isotopic composition, bulk nitrogen isotopic composition, and bound saturated fatty acid (BSFA) concentrations in sediment cores. A rapid increase in the supply of organic matter (OM) to DC began after the 1950s, while the environment and trophic status of BST remained constant as indicated by characteristics of OM input to sediments. The BSFA ratios of nC14 + nC16 + nC18/nC24 + nC26 + nC28 increase upward from 7 to 13 in the DC core, which are significantly greater than those from BST (2 to 3). This result is consistent with algae or bacteria being the dominant contribution of the OM increase induced by eutrophication in DC. The positive shift of nC16 compound-specific δ (13)C in the upper section might be an indicator of excess algal productivity, which was observed in the two lakes. The positive shifts of compound-specific δ (13)C of other BSFAs were also observed in the upper section of the core only from DC. The observed trends of compound-specific δ(13)C of BSFA originated from different sources became more consistent, which reflected the intensified eutrophication had profoundly affected production and preservation of OM in DC. The results observed for BST indicated that accumulation of algae did not affect the entire aquatic ecosystem until now.