Salinity impacts on n-alkanes in lake sediments of the Badain Jaran Desert, Northwestern China: Implications for paleoclimate reconstruction

Abstract

n-Alkanes in lake sediments are essential biomarkers for paleoclimate research, yet the influence of lake salinity on their distribution remains unclear. This study investigates this relationship by analyzing sediments from eight lakes in the Badain Jaran Desert, all subject to similar climatic conditions but varying in salinity. Soil samples from the shoreline vegetation belt and suspended particle matter (SPM) were collected to identify the origin of plant input in the lake sediments. Additionally, sediment samples from the littoral zone to the lake center were all gathered to evaluate the salinity effects at different water depths. Key indexes such as content, the proportion of aquatic macrophyte (Paq), average chain length (ACL), and carbon preference index (CPI) of n-alkanes were examined to elucidate salinity effects. The result showed that the surrounding vegetation belt is the primary source of n-alkanes in lake sediments, with minimal contributions from SPM. Increased salinity was found to decrease CPI in the littoral zone, while also reducing Paq and increasing ACL in the lake bottom sediments. Changes of Paq, ACL and CPI in sediments are not attribute to variations in vegetation belt input but rather suggest that high salinity enhances n-alkane degradation, particularly favoring the degradation of mid-chain compounds in lake bottom sediments. Consequently, the reliability of n-alkane indexes as indicators of aquatic macrophyte in deep lake cores may be compromised by salinity. This study underscores the importance of accounting for salinity effects when using n-alkanes in reconstructing paleoclimate and suggests that their potential as indicators of lake salinization merits further attention.