[Molecular Signatures of Dissolved Organic Matter in the Paihe River and Its Tributaries]

Dissolved organic matter (DOM) is an abundant and critical component of aquatic ecosystems, participating in many physicochemical and biogeochemical processes. The Paihe River is the only inflow river in the Jianghuai section of "Yangtze-Huaihe water diversion" clear water gallery project; however, its DOM molecular composition information and characteristics are still unclear. In this study, the molecular characterization of DOM in the Paihe River and Guangming Dayan River was determined using Orbitrap mass spectrometry. The Pearson's correlation and principal component analysis (PCA) were used to study the relationship between molecular composition information, characteristics, and sources of DOM in two rivers. The results showed that the molecular weight and oxygen content of DOM molecules in the Paihe River were relatively low; the molecular weight, aromaticity, and unsaturation of DOM molecules in the Guangming Dayan River were relatively high. From the element composition and compound composition of the two rivers' DOM, both rivers were mainly composed of CHO-compounds, lignin, and tannins derived from land plants, which indicates that both rivers were severely affected by terrestrial input. There were high percentages of CHOS, protein, and lipid compounds of DOM in the Paihe River. According to the results of the Pearson's correlation and PCA analyses, the DOM molecules of the Paihe River were also influenced by wastewater from sewage treatment plants, urbanization processes, and microbial activity. Molecular composition information and characteristics of DOM can provide a detailed reference to improve the theoretical support for the Paihe River clear water gallery project.