Long-chain n-alkenes in recent sediment of Lake Lugu (SW China) and their ecological implications

Long-chain n-alkenes showing a predominance of n-C-25:1 and n-C-27:1 were detected in recent sediment of Lake Lugu, an oligotrophic alpine lake in Yunnan Province, SW China. The abundances of n-C-25:1 and n-C-27:1 alkenes varied considerably in the sediment core, most obviously in showing higher values during the period of 1821-1982, followed by a significant decrease between 1982 and 2012. Such variations were similar to those of long-chain 1,15-alkyl diols, biomarkers of eustigmatophytes, and a significant correlation was observed between n-C-25:1 (or n-C-27:1) alkene and C-32 1,15-alkyl dial in the sediment core. This correlation and the fact that long-chain n-alkenes in some eustigmatophytes (e.g., Nannochloropsis sp.) were dominated by C-25 and C-27 compounds indicates that eustigmatophytes were the most likely contributor of the long-chain n-alkenes (especially the n-C-25:1 and n-C-27:1 alkenes) in Lake Lugu sediment. Chlorophytes, on the other hand, cannot be excluded as a possible contributor of the long-chain n-alkenes because these algae are common in Lake Lugu and they are known to biosynthesize n-C-27:1 alkene. Productivities for some species of eustigmatophytes and chlorophytes considerably decreased when the lake water was heavily influenced by catchment soil erosion and anthropogenic sewage inputs. (C) 2015 Elsevier GmbH. All rights reserved.