OPTICAL CHARACTERIZATION, DISTRIBUTION AND SOURCES OF CHROMOPHORIC DISSOLVED ORGANIC MATERIAL(CDOM) IN THE CHANGJIANG RIVER ESTUARY IN JULY 2014

Absorption and fluorescence spectroscopy, along with dissolved organic carbon(DOC) quantification, were employed to examine the sources and estuarine mixing behavior of chromophoric dissolved organic matter(CDOM) in the Changjiang River estuary in July 2014. CDOM abundance(as quantified by the absorption coefficient at 355 nm, a(355)), the absorption spectral slope over 275-295 nm(S275-295), and the specific UV absorbance at 254 nm(SUVA254) were all generally conservative across the freshwater-saltwater transitional zone. A localized elevation of CDOM occurred downstream in the mouth of the Huangpu River, revealing a subtle difference in the mixing pattern of CDOM between the North Port and the South Port, where as the constitutive property between the two ports was similar. DOC concentration([DOC]) can be predicted from the CDOM absorption coefficients at 275 nm(a(275)) and 295 nm(a(295)): ln[DOC] = 4.94–0.87ln[a(275)] + 0.90ln[a(295)], a(275)8.0 m–1; ln[DOC] = 4.77–6.79ln[a(275)] + 8.05ln[a(295)], a(275)≥8.0 m–1. The regression results demonstrate that CDOM absorbance could be used as the DOC tracer along the Changjiang River estuary. EEMs-PARAFAC(excitation-emission matrix fluorescence spectroscopy-parallel factor) analysis identified three humic-like components(C2, C4, and C5) and three protein-like components(C1, C3 and C6). The humic-like components possessed similar origins and correlated with a(355) and salinity. The protein-like components C1 and C6 were not significantly correlated to salinity and a(355), suggesting the protein-like components were closely related to the in situ microbial activities.