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Characterization of CDOM in reservoirs and its linkage to trophic status assessment across China using spectroscopic analysis

Shang, Yingxin, Song, Kaishan, Jacinthe, Pierre A., Wen, Zhidan, Lyu, Lili, Fang, Chong, Liu, Ge
Journal of hydrology 2019
absorbance, absorption, altitude, dissolved organic matter, drinking water, eutrophication, fluorescence, fluorescence emission spectroscopy, humification, hydrology, models, nutrients, sewage, spectral analysis, wastewater, water quality, water reservoirs, China
Chromophoric dissolved organic matter (CDOM) represents the optically active component of the DOM pool, and originates from both allochthonous and autochthonous sources. The fluorescent characteristics of dissolved organic matter (FDOM) has been widely used to trace CDOM sources and infer its composition. However, little is known about the optical and fluorescent properties of CDOM in drinking water reservoirs, and the variability of CDOM properties along trophic gradients in these aquatic systems. A total of 536 water samples were collected between 2015 and 2017 from 131 reservoirs across China to characterize CDOM and FDOM properties using both light absorption and fluorescence spectroscopies, and examine relationships with water-quality condition as expressed by the modified trophic state index (TSIM) of the reservoirs (range: 12 <TSIM< 78). With increased reservoir trophic status, CDOM absorption coefficients at 254 nm (aCDOM(254)) and total fluorescence of FRI-EEMs (excitation-emission matrix coupled with fluorescence regional integration) increased significantly (p<0.01). Our results indicated that the nutrients in aquatic systems and the social economy factors (including wastewater, sewage, cultivated land, GDP, population) and altitude affect the CDOM absorption and fluorescence significantly (p<0.05). Most importantly, we proposed a new classification standard associated with eutrophic status via CDOM humification index (HIX) due to the significant correlation between each other (p<0.01). HIX less than 4 was corresponding to TSIM less than 30 as oligotrophic states; 4<HIX≤12 was corresponding to TSIM less than 50 as mesotrophic states; 12<HIX≤18 was corresponding to TSIM less than 70 as eutrophic states; HIX more than 18 is defined as hypereutrophic status with TSIM>70. This method highlights the importance of CDOM fluorescence for aquatic DOM input and strengthens the linkage between the trophic status index and CDOM characteristics, it also contributes to establish a new rapid assessing model with quick experimental measurements to monitor the trophic status of water reservoirs.