[Spatial Pattern and Source Apportionment of Dissolved Organic Matter in Quanmin Reservoir Watershed Based on...

The sources and composition of dissolved organic matter （DOM） in water bodies exhibit high spatiotemporal heterogeneity. Taking the Quanmin Reservoir watershed in Sichuan Province as the study area， water samples were collected from four inflow rivers and nearby pollution sources such as farmland drainage and sewage treatment plant effluents during the wet and dry seasons. Three-dimensional excitation-emission matrix spectra （3D-EEMs） combined with parallel factor analysis （PARAFAC） was used to analyze the composition， distribution characteristics， and sources of DOM in the study area. The correlation between water quality parameters and DOM parameters was further used to clarify the sources of DOM. The results showed that： ① The average concentrations of TP， NH₄⁺-N， NO₃^--N， TN， and DOC in the Quanmin Reservoir watershed were all lower in the wet season than in the dry season， and TN was the main pollutant in the watershed. ② The PARAFAC analysis identified three components in the DOM of the Quanmin Reservoir watershed， including terrestrial humic-like C1 （E_x/E_m = 360/425 nm）， visible light region fulvic-like C2 （E_x/E_m = 400/480 nm）， and microbial metabolic products C3 （E_x/E_m = 335/417 nm）. ③ The total fluorescence intensity of DOM was higher in the wet season than in the dry season. The relative abundance of terrestrial humic-like C1 was the largest in both periods， accounting for 37.40% and 37.52%， respectively. The average maximum fluorescence intensity of DOM in the two periods was in the order of Xiongjiagou River > Guxian River > Xixi River > Motan River. ④ Based on fluorescence spectral parameters and multi-parameter correlation analysis， the three components of DOM in the Quanmin Reservoir watershed demonstrated homogeneity， and DOM was mainly of terrestrial origin， showing weak humification characteristics. Water quality parameters in different periods had different degrees of correlation with DOM components and fluorescence parameters. The research results can provide a basis for the source tracing of nitrogen and phosphorus pollutants and water environment management in the Quanmin Reservoir watershed.