Carbon chain length distribution in n-alkyl lipids: A process for evaluating source inputs to Lake Qinghai

Lake sediments generally contain a mixture of terrestrial and aquatic source inputs, and determining the major inputs is important for understanding geological records in paleoenvironment and paleoclimate research. In this study we describe the distribution of n-alkanes and n-fatty acids (FAs) in representative modern plants from around Lake Qinghai. We found a significant difference in the average length of n-FA carbon chains (ACL Fa(16-32)) in terrestrial (23.3) and aquatic plants (18.6). The results reveal that ACL Fa(16-32) may essentially serve as a proxy for evaluating the major source inputs to lake sediments. Assessment of surface sediments from the lake showed that the FAs originated from a mixture of inputs, with the aquatic source input predominant at most sites. Additionally, the delta D values of sediment mid-chain n-acids (C-22) showed a relationship with the ACL Fa(16-32) proxy: an increased Fa ACL corresponded to more negative hydrogen isotope ratio values. We suggest that different sources should be considered and ACL Fa(16-32) could be a potential calibration proxy before using delta D values to extract reliable isotopic information from lake water. More attention should be paid to source inputs and their relationship to other geochemical proxies in future studies of lake sediments. (C) 2012 Elsevier Ltd. All rights reserved.