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

Abstract

a b s t r a c tLong-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 diol 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.

Potential bioavailability of pyrogenic organic matter resembles natural dissolved organic matter pools

“…Fatty acids and n-alkanes biomass burning by-products are generally reduced in chain length in comparison to their un-burned counterparts 67 , and thus may be relatively bioavailable compared to other lipids. Additionally, we note that previous work has shown fast degradation of combustion-derived lipids in soils; 67 as well as high n-alkene metabolism under anaerobic conditions (in particular by sulfate-reducing bacteria [68][69][70][71] ), n-alkene metabolism in natural sediments, 71,72 and a range in lipid reactivities at the sediment-water interface. 73 While work on n-alkene metabolism in aerobic settings is limited, the comparative bioavailability of n-alkenes and known microbial degradation pathways suggests diverse microbiomes in sediments may metabolize these compounds as part of natural biogeochemical cycles.…”

Molecular signatures of organic particulates as tracers of emission sources

“…Anyway, further investigations are necessary to confirm this hypothesis and search for alternative solutions. For sake of completeness, it is worth to note that the occurrence of ≥ C 20 alkenes and polyalkenes in estuarine and coastal sediments, even exceeding the corresponding n-alkanes, has been associated with algae and phytoplankton (Requejo and Quinn 1983 ; Yongdong et al 2015 ).…”