Dissolved Organic Matter Characteristics and Composition of Saline Lakes in the Badain Jaran Desert, China

Elucidating the characteristics and molecular composition of dissolved organic matter (DOM) is critical to understanding carbon cycling in increasingly saline lakes in arid and hyperarid areas; however, the molecular signatures of DOM in these widely distributed saline lakes remain poorly understood. Here, variations in DOM characteristics and ages with salinity were investigated across 10 small saline lakes within the Badain Jaran Desert based on absorption and fluorescence spectroscopy, Fourier transform ion cyclotron resonance mass spectrometry, and ¹⁴C-isotopic analysis. The results showed that dissolved organic carbon (DOC) significantly increased with salinity, and the ¹⁴C age of solid-phase extracted DOM ranging 385–3935 years before present did not correlate with salinity across lakes. With increasing salinity, the DOM aromaticity, DOC-specific abundances of fluorescent components, and relative abundance of lignin-like components all decreased, whereas the relative abundance of lipid-like components increased. Regarding halogen-containing DOM, the brine lakes showed higher relative abundances of chlorine-containing lignin- and lipid-like components but comparable relative abundances of bromine-containing components, supporting preferential chlorination over bromination. This study demonstrates the strong impacts of salinization on DOM accumulation and chlorination in inland saline lakes and highlights the critical role of brine lakes as a persistent carbon pool.