[Spectral Characteristics of Dissolved Organic Matter in the Yangtze River Basin and Its Response to Natural and Anthropogenic Activities].

Abstract

Dissolved organic matter （DOM） is involved in many biogeochemical processes and plays an important role in aquatic ecosystems. Notable differences appear in land use types in the upper, middle, and lower reaches of the Yangtze River, and the distribution characteristics and optical properties of DOM and its response to natural and anthropogenic activities vary greatly in long-distance transport. This study systematically collected 84 water samples from the upper, middle, and lower reaches of the Yangtze River Basin and used ultraviolet-visible spectroscopy （UV-vis）, three-dimensional fluorescence spectroscopy combined with fluorescence region integration （FRI）, and parallel factor analysis （PARAFAC） to analyze the distributional and compositional characteristics of DOM in the Yangtze River Basin and to explore the response of DOM to natural and anthropogenic activities. The results showed that： ① The average DOC concentration in the Yangtze River Basin was 3.17 mg·L^-1, and the average DOC concentrations in the upper, middle, and lower reaches of the river were 2.75, 3.24, and 4.83 mg·L^-1, respectively, showing an upward trend. ② The FRI showed that humic acid-like fractions （P_Ⅴ） accounted for the highest percentage of DOM in the Yangtze River Basin, with an average value of 60.77%, and PARAFAC resolved three fluorescent components, namely C1 （UAC-like humic acid）, C2 （tryptophan-like）, and C3 （UV-like humic acid）. ③ DOM in the Yangtze River Basin was generally affected by the input of microbial and terrestrial sources together, and the upstream DOM had a low biogenicity index （BIX）, which was dominated by terrestrial inputs. The middle reaches of the DOM had a higher number of aromatic substances, and hydrophobicity components were more abundant, showing strong humus and weakly neophytic autochthonous source characteristics. The downstream DOM had small relative molecular mass and obvious autochthonous source characteristics and was substantially affected by microbial activities. The results of this study can help to identify the biogeochemical cycles of DOM on a regional scale and provide a basis for water resource management and water environment protection in the Yangtze River Basin.