Fatty acid and alcohol compositions in lacustrine sediments as indicators of environment and ecosystem of lakes in Eastern China

Abstract

During the past hundred years, the majority of lakes along the middle and lower reaches of the Yangtze River (MLRYZ) have been greatly impacted by human intervention, resulting in a significant spatial heterogeneity in water and ecosystem quality. We quantified the fatty acid (FA), n-alkanol, sterol and long-chain alkyl diol content of surface sediments of MLRYZ lakes in order to determine how ecological differences (algae versus macrophyte-dominated state) and trophic status influence the composition, origin and abundance of lipid biomarkers in the sediments. Based on the results, variation in FAs appears to be mainly controlled by the type of organisms within the lakes. Short-chain n-alkanoic acids, monounsaturated FAs (MUFAs) and polyunsaturated FAs (PUFAs) were generally more abundant in sediments of algal lakes (lacking macrophyte growth) than in lakes with macrophyte growth. The opposite trend was apparent for long-chain n-alkanoic acids. Ratios of (C26 + C28)/(C22 + C24) n-alkanoic acids differed significantly between macrophyte and algal lakes. In the alcohol fraction, lipid biomarker abundance appeared to be controlled by trophic status of the lake, with the exception of cholesterol and long-chain n-alkanols whose abundances were closely related to the present organisms and exhibiting greater abundances in algal lakes. Enhanced levels of total phosphorus (TP) and total nitrogen (TN) in a lake create greater concentrations of C32 1,15 alkyl diol and brassicasterol respectively, while the abundance of dinosterol and the ratio of dinosterol/brassicasterol decline in line with increase in TP and TN, respectively. Ratios of (C26 + C28)/(C22 + C24) n-alkanol were also greatly influenced by the type of organisms present, exhibiting higher values in algal lakes. The sensitivity of these sediment lipid biomarker responses points to a potentially useful role as proxies for biological community types and trophic status in paleolimnology studies.