Sources and Spatial Variation of Dissolved Organic Matter in Summer Water of Inflow Rivers Along Chaohu Lake Watershed

The sources and spatial variations of dissolved organic matter (DOM) in summer water of inflow rivers (FL, HB, QY, ZH, and NF) along the Chaohu Lake watershed were analyzed using the ultraviolet-visible absorption spectrum (UV-vis) method and three-dimensional excitation emission matrix fluorescence spectroscopy-parallel factor analysis (EEM-PARAFAC). The specific ultraviolet absorbance of DOM at 254 nm in the NF river was lower than in other rivers, and the spectral slope ratio (SR) of the NF river was higher than that of the HB river. This showed that the urban runoff inputs reduce the aromaticity of DOM in the NF river water, but has little effect on the molecular weight. The high fluorescence index (FI) and biological index, and the low humification index, indicated the main autochthonous sources of the DOM in the NF river. Four humic-like components (C1-C4), comprising terrestrial organic matter (C1, C3, and C4) and microbial degradation products (C2), and two protein-like components (C5 and C6) were identified as the main sources of DOM in the inflow rivers along the Chaohu Lake watershed. The dissolved organic carbon and DOM fluorescence components in the river water exhibited spatial variation along the direction of flow. The DOM in water from FL, HB, QY, and ZH was sourced from soil runoff inputs, whereas in NF water, it was mainly sourced from urban runoff and wastewater treatment plant effluents.