Seasonal Variations of CDOM Optical Properties in Rivers Across the Liaohe Delta

Abstract

Absorption and fluorescence properties of chromophoric dissolved organic matter (CDOM) in rivers across the Liaohe River Delta, a large estuary located in the southern region of northeast China, were investigated using spectroscopy and fluorescence to analyze CDOM characteristics, composition and sources in winter (January), spring (April and May) and autumn (September) 2013. Results indicated that CDOM absorption of ice samples was lower compared to water samples. CDOM absorption also showed significant spatial variation but not temporal variation. In contrast, dissolved organic carbon (DOC) concentrations showed obvious temporal characteristics. A stronger linear relationship was found between CDOM absorption and DOC concentration in winter (water, R 2 = 0.95, p < 0.001; ice, R 2 = 0.85, p < 0.001) compared to samples from other seasons (April, R 2 = 0.51, p < 0.01; May, R 2 = 0.34, p < 0.05; September, R 2 = 0.45, p < 0.01). CDOM fluorescence varied over a large range across seasons, with the highest levels observed in January at the Xisha River (XSR). Moreover, strong linear relationships were also observed between CDOM absorption and fluorescence intensity at 355 nm [Fn(355)] in January (R 2 = 0.87, p < 0.001), May (R 2 = 0.76, p < 0.001) and September (R 2 = 0.94, p < 0.001). Also based on study findings, CDOM fluorophores identified by 3-D excitation-emission matrices (EEMs) illustrated that the rivers across the Liaohe Delta were seriously polluted by anthropogenic disturbances, exhibiting strong protein-like fluorescence of CDOM in the water column. In addition, the results also confirm that absorption and EEMs would be useful tools for tracing the sources and characteristics of CDOM and monitoring riverine water quality.