Characterizing Chromophoric Dissolved Organic Matter (CDOM) in Lake Honghu, Lake Donghu and Lake Liangzihu Using Excitation-Emission Matrices (EEMs) Fluorescence and Parallel Factor Analysis (PARAFAC)

Little is known about DOM characteristics in medium to large sized lakes located in the middle and lower reaches of Yangtze River, like Lake Honghu, Lake Donghu and Lake Liangzihu. Absorption, fluorescence and composition characteristics of chromophoric dissolved organic matter (CDOM) are presented using the absorption spectroscopy, the excitation-emission matrices (EEMs) fluorescence and parallel factor analysis (PARAFAC) model based on the data collected in Sep. -Oct. 2007 including 15, 9 and 10 samplings in Lake Honghu, Lake Donghu and Lake Liangzihu, respectively. CDOM absorption coefficient at 350 nm a(350) coefficient in Lake Honghu was significantly higher than those in Lake Donghu and Lake Liangzihu (t-test, p<0. 001). A significant negative correlation was found between CDOM spectral slope in the wavelength range of 280 similar to 500 nm (S-280 similar to 500) and a(350) (R-2 = 0. 781, p<0. 001). The mean value of S-280 similar to 500 in Lake Honghu was significantly lower than those in Lake Donghu (t-test, p<0. 01) and Lake Liangzihu (t-test, p<0. 001). The mean value of spectral slope ratio SR in Lake Honghu was also significantly lower than those in Lake Donghu and Lake Liangzihu (t-test, p<0. 05). Two humic-like (C1, C2) and two protein-like fluorescent components (C3, C4) were identified by PARAFAC model, among which significant positive correlations were found between C1 and C2 (R-2=0. 884, p<0. 001), C3 and C4 (R-2=0. 677, p<0. 001), respectively, suggesting that the sources of the two humic-like components as well as the two protein-like components were similar. However, no significant correlation has been found between those 4 fluorescent components and DOC concentration. The fluorescence indices of FI255 (HIX), FI265, FI310(BIX) and FI370 in Lake Donghu were all significantly higher than those in Lake Liangzihu (t-test, p <0. 05) and Lake Honghu (t-test, p<0. 01), indicating that the eutrophication status in Lake Donghu was higher than Lake Honghu and Lake Liangzihu.