[Characterizing Sources and Composition of Chromophoric Dissolved Organic Matter in a Key Drinking Water Reservoir Lake Tianmu].

Abstract

Lake Tianmu is an important source of drinking water, and its water quality can influence ecosystem service functions. Unraveling the sources and composition of chromophoric dissolved organic matter (CDOM) that can affect water treatment processes is necessary to maintain water supply safety and ecosystem service functioning of Lake Tianmu. Samples were collected monthly in 2017 and analyzed for CDOM absorbance and fluorescent spectra using parallel factor analysis (PARAFAC) to investigate the spatial and temporal variations of CDOM sources and composition in Lake Tianmu. PARAFAC results showed that CDOM in Lake Tianmu was mainly composed of a microbial humic-like component C1 (44.2%±9.8%), followed by a tryptophan-like component C2 (29.2%±4.3%), tyrosine-like component C3 (17.2%±13.1%), and terrestrial humic-like component, C4 was the lowest (9.4%±2.4%). The CDOM abundance a(254) and fluorescence intensities of C1 and C2 were significantly higher in the river mouths than in the downstream lake regions, whereas the spectral slope S_275-295 was significantly lower in the river mouths (t-test, P<0.05), indicating that allochthonous inputs cause an elevated degree of humification and relative increase in the molecular weight of CDOM in the inflowing river mouths. Seasonal differences in CDOM composition were mainly ascribed to the a(254) and fluorescence intensities of C1, C2, and C4 being significantly higher in the summer and autumn than in the winter and spring (t-test, P<0.05). Our results showed that the influences of different seasons on CDOM composition comprise differences in rainfall and runoff input, as well as water temperature, thermal stratification, phytoplankton biomass, and mineralization of CDOM by light and microbes.