Characterizing sources and optical composition of chromophoric dissolved organic matter in Lake Xingkai, a large boundary lake in China

Research on the sources and optical composition of Chromophoric dissolved organic matter (CDOM) is of great significance to the water quality protection of the Lake Xingkai. CDOM absorption coupled with excitation-emission matrices and parallel factor analysis (EEMs-PARAFAC) were used to explore the sources and optical composition of DOM in Lake Xingkai. Four fluorescent components were identified using EEMs-PARAFAC, including a terrestrial humic-like C1, a microbial humic-like C2, a tyrosine-like C3, and a tryptophan-like C4. The fluorescence characteristic of C1is a potential surrogate tracing the variability of DOC and TN concentrations. DOM absorption a254, the integration ratio of the fluorescence peak C to peak T (IC:IT), the spectral slope of CDOM absorption S275-295 and DOC concentrations were associated closely with C1-C2, and C4 in Lake Xingkai. This indicates that terrestrial input is an important source of DOM to Lake Xingkai. Significantly higher mean a254 and DOC concentrations were found in the Small Lake Xingkai than in the Great Lake Xingkai, indicating that the levels of CDOM in Small Lake Xingkai was higher than that in Great Lake Xingkai. The mean IC:IT and fluorescence intensities of C1, C2, and C4 were significantly higher in the Small Lake Xingkai than that in the Great Lake Xingkai, whereas S275-295 and SR was significantly lower in the Small Lake Xingkai. The mean score of PC1, positively associates with DOC, TN, DTN, NO- 3-N, a254, IC:IT, SUVA254, C1, C2 and C4, in Small Lake Xingkai was significantly higher than that in Great Lake Xingkai. These results indicated that substantial terrestrial DOM with enhanced aromaticity were exported to the Small Lake Xingkai, probably due to an enhanced riverine input and agricultural non-point source pollution in the Small Lake Xingkai watershed. Therefore, a better management of riverine input to the lake due to regional fishery, agricultural land use, and tourism in the upstream watershed is needed. © 2022, Editorial Board of China Environmental Science. All right reserved.