Origin, Composition and Spectroscopic Characteristics of Dissolved Organic Matter in Brine from Yuncheng Salt Lake

Dissolved organic matter (DOM) in salt lake brines comprises organic compounds dissolved in high-salinity aquatic systems. With complex composition and diverse sources, DOM significantly influences biogeochemical cycles, mineral formation, and resource development in salt lakes. However, few studies have investigated the characteristics and sources of DOM in salt lake brines. In this study, a DOM sample (YC-4) from brine of Shanxi Yuncheng Salt Lake was isolated and characterized using FT-ICR-MS, nuclear magnetic resonance spectroscopy, three-dimensional fluorescence spectroscopy, and parallel factor analysis. The results demonstrate that YC-4 DOM exhibits rich chemical diversity, primarily composed of lignin/CRAM-like compounds (54.26%), tannins (16.75%) and proteins (13.43%). The predominant carbon forms in YC-4 DOM were aliphatic C-O bonded compounds (33.74%), aliphatic compounds (24.31%), and carboxylic acid compounds (23.95%). YC-4 DOM consists of five fluorescent components: marine-like humic substances, two types of humic-like substances, fulvic-like substances, and one protein-like substance. The fluorescence signature, characterized by high fluorescence index (FI 1.99), low humification index (HIX 0.66), and high biological index (BIX 1.27), collectively indicates that the DOM in Yuncheng Salt Lake brine is predominantly autochthonous, weakly humified, and highly bioavailable. This study reveals the DOM feature within the “human–environment coupled system” of Yuncheng Salt Lake. The findings provide a scientific basis for the sustainable utilization of its brine DOM resources and further enrich the theoretical system of DOM biogeochemical cycle in high-salinity lake system.