DOM is the largest reservoir of organic carbon in the world, and it plays a crucial role in the biogeochemical cycles of natural water bodies. A river is a transition area connecting source water and receiving water that controls the DOM exchange between them. Therefore, in this study, ultraviolet visible spectroscopy (UV-vis) and three-dimensional fluorescence spectroscopy (EEMs) combined with parallel factor analysis (PARAFAC) were used to analyze the spectral characteristics and sources of dissolved organic matter in the Fuhe River, Xiaobai River, Baigouyin River, and Puhe River of Baiyangdian. The results showed that a245 and a355 in the Fuhe River and Xiaobai River were significantly higher than those in the Baigouyin River and Puhe River. E2/E3 showed that the DOM relative molecular mass of the inflow river water body was Puhe River > Baigouyin River > Fuhe River > Xiaobai River. Three components, tyrosine-like (C1), terrigenous humus (C2), and tryptophan-like (C3), were determined using three-dimensional fluorescence through PARAFAC. There was no difference among the fluorescence components (P>0.05), but there were differences among the C2 and C3 components (P<0.05). The proportion of easily degradable protein-like components (C1+C3) was higher than that of humus-like components (C2). The autogeny index BIX was greater than 1, and the humification index HIX was less than 4, indicating that the autogeny characteristics of the river bodies were obvious, and the humification degree was weak. The FI index was the highest (1.96±0.25), and the HIX index was the lowest (0.46±0.08), and the self-generated source characteristics gradually strengthened along the direction of the river entering the lake, indicating that the water body of the Fuhe River showed higher endogenous and autogenic characteristics. Based on the correlation analysis of fluorescence components and characteristic parameters of DOM, the correlations between the Fuhe River and Xiaobaihe River and between the Baigouyin River and Puhe River bodies were similar. The correlation between fluorescence components of DOM and water quality parameters of each lake was significantly different, and it was strongly correlated with nitrogen and phosphorus in water. According to multiple linear regression analysis, there was no significant difference among C1 components, but there was a significant difference between C2 and C3 components. In summary, the carbon cycle process of Baiyangdian Lake was further understood through the study on the DOM spectral characteristics and sources of the inflow river waters in the summer flood season.
Keywords: Baiyangdian Lake; dissolved organic matter（DOM）; inflow rivers; three-dimensional fluorescence spectroscopy（EEMs）; ultraviolet-visible spectroscopy（UV-vis）.