A comparison of the distribution and sources of organic matter in surface sediments collected from northwestern and southwestern plateau lakes in China

Surface lacustrine sediments from six plateau lakes in China were analysed for total organic carbon (TOC), total nitrogen, delta C-13(org), delta N-15(total), aliphatic hydrocarbons, fatty acids (FAs), and alkanols. The FAs and alkanols were fractionated into free and bound subfractions to facilitate investigation of their sources. Higher average TOC levels were observed in sediments from southwestern plateau lakes than in those from northwestern plateau lakes. The sediments from the southwestern plateau lakes may have been contaminated with petroleum hydrocarbons from anthropogenic activities. The molecular compositions of n-alkanes, n-alkanols, and FAs extracted from the lacustrine sediments showed different responses to environmental changes. Most of the n-alkanol and FA distributions were dominated by short-chain components originating from algae and bacteria. However, the presence of long-chain n-alkanes indicate the presence of predominantly terrestrial organic matter (OM) in the sediment samples from the northwestern plateau lakes in China, suggesting that secondary components derived from post-depositional microbial activity were key contributors to the n-alkanols and FAs. Aquatic FAs derived from algae and anaerobic bacteria were a major component of the sedimentary OM and accounted for 65.1-90.2% of the total lipid concentrations.