Characterization of DOM(dissolved organic matter) in Yangtze River using 3-D fluorescence spectroscopy and parallel factor analysis

Water samples were collected from Yangtze River basin across 4000 km during September, 2009.Five fluorescence components (3 humic-like and 2 protein-like components) were identified by 3-dimension fluorescence spectroscopy (EEMs) combined with parallel factor analysis (PARAFAC) combined with a₃₅₀ to elucidate composition, source and transformation processes of dissolved organic matter (DOM) in the Yangtze River. Dissolved organic carbon (DOC) increased remarkably from Wanzhou to the Three Gorge Dam and thereafter remained constant in the lower reach. The sum of all 5 components (∑Fluo) showed the similar trend of variation, which correlated linearly with DOC (R²=0.92) indicating that EEMs is a powerful tool to trace DOM in the Yangtze River. The protein-like component (∑P) accounted for 1/4 of ∑Fluo with apparently weak correlations with DOC and chlorophyll-a, which implied that the riverine DOM is not dominated by autochthonous production. Humic-like(H₁, H₂, H₃) components showed different correlations with DOC, especially in the lower reach, where H₃(E_x/E_m:250/450~485 nm) was accumulated, while the other components (H₁, H₂) and a₃₅₀ seemed to be degraded faster than H₃. All the fact indicated that DOM might be subjected to selective biological and photochemical degradation processes in Yangtze River.