[Characterization of Spatial Distribution and Source Analysis of Dissolved Organic Matter in the Three Gorges...

Dissolved organic matter （DOM） in inland waters plays an important role in the regional and global carbon cycles. However, limited comprehensive studies are available on the spectral characterization and traceability analysis of DOM in river systems affected by crucial hydraulic projects. This study focuses on the main stream and typical tributaries within the Three Gorges Reservoir Area. Ultraviolet-visible absorption spectroscopy （UV-vis） and three-dimensional fluorescence spectroscopy （3D-EEMs）, combined with parallel factor analysis （PARAFAC）, were used to systematically investigate the spectral properties and spatial distribution patterns of DOM in the reservoir area. The findings demonstrated that the riverine DOM in the Three Gorges Reservoir Area was influenced by a combination of endogenous and terrestrial sources, where endogenous contributions were predominant. Moreover, the riverine DOM displayed a weak humification characteristic and strong autochthonous signal. Notably, DOM in the main stream exhibited a higher relative molecular weight, greater degree of carbon skeleton polymerization, and more complex structure. The FI values of the main stream and typical tributaries in the Three Gorges Reservoir Area ranged from 1.79 to 2.48 and 1.62 to 2.03, with mean values of 1.95 and 1.93, respectively. Additionally, the mean values of BIX in the main stream and tributaries were 0.92 and 0.85, respectively. The results of the FI and BIX analyses indicated that the riverine DOM of the reservoir area was driven by both endogenous and terrestrial sources, with the prevalence of endogenous sources. EEMs-PARAFAC analysis revealed that, in addition to the analogous C1 （humic-like） and C2 （tyrosine-like） fractions, DOM in the main stream also included a mixed humic-like fraction, C3. Correlation analysis revealed that the spectral characteristics of DOM in the main stream and representative tributaries in the Three Gorges Reservoir Area exhibited pronounced spatial heterogeneity and correlation because of the effects of anthropogenic disturbances, land use, and cumulative effects of the tributaries. These findings provide scientific insights for the conservation and management of aquatic ecosystems in the Three Gorges Reservoir Area.