Optical and Molecular Signatures of Dissolved Organic Matter in Xiangxi Bay and Mainstream of Three Gorges Reservoir, China: Spatial Variations and Environmental Implications

Kai Wang ^a,YuPang ^a,ChenHe ^b,PenghuiLi ^c,ShangbinXiao ^d, Yongge Sun ^a, Qiong Pan ^b,YaheZhang ^b, Quan Shi ^b,⁎,DingHe ^a,⁎

^a Institute of Environmental and Biogeochemistry (eBig), School of Earth Sciences, Zhejiang University, Hangzhou 310027, China 

^b State Key Laboratory of Heavy Oil Processing, China University of Petroleum, Changping District, Beijing 102249, China 

^c Department of Ocean Science and Engineering, Southern University of Science and Technology, Shenzhen 518055, China 

^d College of Hydraulic and Environmental Engineering, China Three Gorges University, Yichang 443002, China

^*Corresponding authors: Email addresses dinghe@zju.edu.cn (D. He), sq@cup.edu.cn (Q. Shi).

DOI: 10.1016/j.scitotenv.2018.12.117

Keywords: Dissolved organic matter; Three Gorges Reservoir; Fourier transform ion cyclotron resonance mass; spectrometry; Optical properties; Molecular composition; Spatial variations

Abstract: With the on-going boom in the construction of dam reservoirs all over the world, the sources and composition of dissolved organic matter (DOM) in fluvial networks are expected to be altered. Considering the importance of DOM as a key biogeochemical component in inland waters, this might bring important ecological and environ-mental influences. However, limited information is available on the molecular composition of DOM in dam res-ervoirs. In this study, the spatial characteristics of DOM composition were investigated in Xiangxi tributary and mainstream of the Three Gorges Reservoir (TGR), the largest freshwater reservoir in the world. The concentration alteration of conservative cations revealed the water intrusion from mainstream into Xiangxi tributary, which mainly controlled the hydrological gradient. One tyrosine-like (C₄), one tryptophan-like (C₂), and two humic-like (C1 and C₃) fluorescent components were identified in fluorescent DOM (FDOM) by parallel factor analysis (PAFACAC), potentially indicating algal, anthropogenic, and terrestrial inputs, respectively. Decreasing trends of C₁, C₃ and C₄ components and an increasing trend of C₂ component were observed from Xiangxi tributary to mainstream, indicating higher terrestrial and algal inputs but lower anthropogenic inputs in Xiangxi tributary compared to mainstream. The Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) char-acterization further revealed substantial heterogeneity of DOM at the molecular level. Interestingly, S-containing compounds related to synthetic surfactants were consistently detected, and their relative abundances