Molecular weight fractionated characterization of dissolved organic matter and its correlation with water quality in the Bahe River Basin, Northwest China

Abstract

Dissolved organic matter (DOM) is one of the core carriers of organic matter decomposition and nutrient regeneration in water. It is an important link of biogeochemical cycle of carbon and nitrogen, and the key content of water environmental science research. We used liquid chromatography-organic carbon detection-organic nitrogen detection (LC-OCD-OND) to investigate the molecular weight distribution of riverine DOM in the Bahe River of Xi'an City and further analyzed its correlation with water quality. The results showed that riverine DOM was composed of biopolymers, humic substances, humus degradation products, and low molecular-weight neutrals, with the ave-rage concentration of 0.15, 1.75, 0.48, 0.36 and 0.002 mg·L-1, respectively. The DOM along the river was in order of urban＞ town＞ river source. The humic substances with molecular weight of 1000-20000 Da accounted for 49.0% of total DOM which followed the order of town＞ waste water treatment plants (WWTPs) effluents＞river estuary＞ river source. The biopolymers with the molecular weight of >20000Da accounted for 5.1% of total DOM, with the sequence of WWTPs effluents＞river estuary＞river source＞town. The allochthonous (terrigenous) DOM produced by WWTPs effluents had the greatest contribution to the riverine DOM. The fractions of DOM with different molecular weights had significant correlations with water quality parameters. The results showed that the molecular weight fractions and abundance of DOM based on LC-OCD-OND could be used as a comprehensive index for water quality monitoring, to characterize the spatial heterogeneity of river water quality, and used for quantitative identification and source apportionment of pollutant components.