[Characterizing Chromophoric Dissolved Organic Matter in Key Lakes in the Middle Reaches of the East Route of the South-North Water Diversion Project].

: Lake Hongze and Lake Luoma are two key lakes located in the middle reaches of the east line of the South-to-North Water Diversion Project. We attempted to unravel the sources and optical composition of CDOM for samples collected from these lakes using excitation-emission matrices (EEMs) and parallel factor analysis (PARAFAC). ① Three fluorescent components were obtained using PARAFAC, including a terrestrial humic-like C1, a tryptophan-like C2, and a tyrosine-like C3. The sources and optical composition of CDOM in the two lakes were, to a large extent, affected by upstream inflow. ② Specifically, fluorescence intensity (Fmax) of the three components C1-C3 in the inflowing river mouths of the two lakes was notably higher than in the other lake regions, and Fmax of the three components during the flood season was significantly higher than during the dry season (t-test, P<0.01). During the flood season, the fluorescence intensity of the terrestrial humic-like component was the highest. This indicates that the source and composition of CDOM in the two lakes are greatly affected by the inflow from the upstream water system, and that the hydrological processes control the abundance and sources of CDOM, especially the terrestrial humic-like C1.③ Significant positive relationships were found between the terrestrial humic-like C1 and the DOC concentrations and CDOM absorption a(254) (r2=0.60, P<0.01; r2=0.88, P<0.01), and the correlation was higher than the other two components. This indicated that the terrestrial humic-like component was the main source of CDOM. In addition, the terrestrial humic-like C1 had a significant positive correlation with SUVA, S275-295, and the integration ratio of the fluorescence peak C to peak T (IC:IT) (r2=0.49, P<0.01; r2=0.61, P<0.01; r2=0.93, P<0.01). It is further revealed that the source and composition of CDOM in the two lakes are greatly affected by land sources. This study reveals the response of CDOM source and composition in Lake Hongze and Lake Luoma to different hydrological scenarios and water transfer processes. Based on these results, the water quality management of the rivers entering the lake should be strengthened during the flood season.