The urbanization process of the Three Gorges Reservoir area (TGRA) shows important impacts on the formation, migration, and transportation of dissolved organic matter (DOM) in rivers. In this study, a high-urbanized river (Taohuaxi) and low-urbanized river (Pulihe) in the TGRA were selected and water samples were collected in spring (April) and summer (August) to analyze the seasonal and spatial characteristics of DOM in the rivers using UV-Vis absorption spectroscopy and three-dimensional fluorescence spectroscopy. The DOC, (the spectral slope of the short wavelength range), (spectral slope ratio), BIX (recent autochthonous contribution), and Fn(280) (relative importance of protein-like substances) of the Taohuaxi and Pulihe Rivers were higher in summer (August) than in spring (April), and CDOM concentration, CDOM/DOC, SUVA (aromatic structure), SUVA (hydrophobic component), E3/E4 (proportion of fulvic acid), (the spectral slope of the long wavelength range), and HIX (the degree of humification) were higher in spring than in summer. The overall averages of the DOC, CDOM concentration, , Fn (280), BIX, and FI were higher in the high-urbanized Taohuaxi River than the low-urbanized Pulihe River, whilst the CDOM/DOC, SUVA, and SUVA were lower in the Taohuaxi River. With the increase of urbanization along the water flow pathways, SUVA and SUVA gradually decreased, while Fn (280) gradually increased. The humus source (FI) of the two rivers in spring and summer is mixed and includes terrigenous and biological sources (plankton and algae) but is mostly endogenous. Furthermore, DOM is characterized by a moderately recent autochthonous contribution. Our study implies a large impact of urbanization on the composition and sources of DOM.
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