Relationship changes between CDOM and DOC in the Songhua River affected by highly polluted tributary, Northeast China.

In this study, the dissolved organic carbon (DOC) concentrations, chromophoric dissolved organic matter (CDOM) absorption coefficient a(254), and excitation-emission matrix fluorescence (EEM) were examined in the Songhua River (SHR) and its highly polluted tributary of Northeast China. Fluorescence regional integration (FRI) was used to identify five fluorescent regions: one tyrosine-like (R1), one tryptophan-like (R2), one fulvic-like (R3), one microbial by-product-like (R4), and one humic-like (R5) regions. The five EEM-FRI regions for all water samples have site-specific properties. Principle component analysis (PCA) was conducted to assess variations in the five FRI regions and the humification index (HIX) for all water samples. For the water samples from the mainstream of SHR, CDOM absorption coefficient a(254) was correlated with either DOC or FRI fluorescent regions (R3 and R5), respectively. FRI R3 region was also correlated with R5 region for the water samples in the mainstream of SHR. However, the determination coefficients (R2) and slopes of these relationships among CDOM absorption, fluorescent regions, and DOC all decreased when the SHR waters were influenced by the highly polluted tributary of Yinma River (YMR) and Yitong River (YTR), which has a negative effect on the estimation of DOC flux transported by the SHR to oceans.