Characterization of CDOM of river waters in China using fluorescence excitation-emission matrix and regional integration techniques

The spatial characteristics of fluorescent dissolved organic matter (FDOM) components in river waters in China were first examined by excitation-emission matrix spectra and fluorescence regional integration (FRI) with the data collected during September to November between 2013 and 2015. One tyrosine-like (R1), one tryptophan-like (R2), one fulvic-like (R3), one microbial protein-like (R4), and one humic-like (R5) components have been identified by FRI method. Principal component analysis (PCA) was conducted to assess variations in the five FDOM components (F-Rl (l = 1, 2, 3, 4, and 5)) and the humification index for all 194 river water samples. The average fluorescence intensities of the five fluorescent components and the total fluorescence intensities F-SUM differed under spatial variation among the seven major river basins (Songhua, Liao, Hai, Yellow and Huai, Yangtze, Pearl, and Inflow Rivers) in China. When all the river water samples were pooled together, the fulvic-like F-R3 and the humic-like F-R5 showed a strong positive linear relationship (R-2 = 0.90, n = 194), indicating that the two allochthonous FDOM components R3 and R5 may originate from similar sources. There is a moderate strong positive correlation between the tryptophan-like F-R2 and the microbial protein-like F-R4 (R-2 = 0.71, n = 194), suggesting that parts of two autochthonous FDOM components R2 and R4 are likely from some common sources. However, the total allochthonous substance FR(3+5) and the total autochthonous substances FR(1+2+4) exhibited a weak correlation (R-2 = 0.40, n = 194). Significant positive linear relationships between F-R3 (R-2 = 0.69, n = 194), F-R5 (R-2 = 0.79, n = 194), and chromophoric DOM (CDOM) absorption coefficient alpha(254) were observed, which demonstrated that the CDOM absorption was dominated by the allochthonous FDOM components R3 and R5