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.

Optical Properties of Chromophoric Dissolved Organic Matter in the Yinma River Watershed and Drinking Water Resource of Northeast China

“…High molecular weight of CDOM is destroyed by photolysis and irradiation due to the bond cleavage, resulting in its transformation to a low molecular weight pool [9]. Compared with the reported riverine waters [5,12,17,29,45], our studies presented signifi cantly opposite results. However, the steep S 250-275 (0.0194) of CDOM and CDOM portion to fulvic acid were found in the Mississippi River [51].…”

“…Lower S r values contained greater allochthonous and higher molecular weight DOM. The effectiveness of S r has been demonstrated with CDOM samples from various waters, ranging from DOC-rich wetlands to photobleached coastal waters and lakes over high-altitude plateaus [29,44]. The coeffi cient of variation (CV) is computed from the fi ltered mean and standard deviation of values.…”

“…[28]. Research has shown that dissolved lignin and phenolic substances (vacular plant) have a signifi cantly positive correlation with a CDOM (350) in various waters, e.g., waters in Hulun plateau [12] and the Congo [9], Liaohe [29], and Elizabeth [30] rivers. Nelson et al (2010) [31] found that CDOM is strongly correlated to apparent oxygen utilization, and it could potentially be used as a tracer of biogeochemical processes in global oceans.…”

Spatial Distribution of Diffuse Attenuation of Photosynthetic Active Radiation and Its Main Regulating Factors in Inland Waters of Northeast China

“…The absorption coefficient at 355 nm (a CDOM (355)) was selected to represent the CDOM concentration [47,48].…”

“…According to previous studies [48], absorption coefficient at 355 nm of CDOM (aCDOM(355)) was regarded as a representative measure of the concentration of CDOM. GIs were calculated with TSM, Chl-a and aCDOM(355) as the factor's behavior data sequences while Kd(PAR) as the systematic behavior data sequence.…”