Absorption and Fluorescence Spectra of Dissolved Organic Matter in Rivers of the Three Gorges Reservoir Area Under the Background of Urbanization

Abstract

Studying the influences of urbanization on the composition, chemical structure, source and migration of dissolved organic matter (DOM) in rivers is of great significance for aquatic ecosystem protection and biogeochemical carbon (C) cycling. The DOM spectroscopic characteristics of the three typical rivers (Taohuaxi, Nanhe, and Puli) with different urbanization levels in the Three Gorges Reservoir area were investigated using the ultraviolet-visible (UV-Vis) absorption spectrum and three-dimensional fluorescence spectroscopy. The results demonstrated that the higher the degree of urbanization in rivers, the greater the concentrations of DOM and chromophoric dissolved organic matter (CDOM), the lower the humification degree and aromaticity of DOM, the smaller the proportion of hydrophobic components, the higher the relative level of protein-like substance concentration in DOM, and the greater the contribution of DOM from freshly autochthonous origins. The DOM of the three rivers was dominated by fulvic acids (E3/E4>3.5), and CDOM concentration was positively correlated with the concentration of DOM (P<0.01). There were significant positive correlations between the humification degree (SUVA254), aromaticity (SUVA280), and hydrophobic component (SUVA260) (P<0.01). The sources of humic substances in the DOM were mixed by terrestrial input and microbial or algae production (reflected by the fluorescence index averages of 1.7157-1.7571), and mainly from microbial sources.