[Sources, Characteristics and Transformation Dynamics of Fluorescent Dissolved Organic Matter in the Silin Reservoir].

The aim of this study was to examine the sources and characteristics of various fluorescent dissolved organic matter (FDOM) components as well as their transformation dynamics. FDOM was determined in the incoming, surface (0 m), deeper (20 m), and outflowing waters of the Silin Reservoir in winter (January), spring (April), summer (June), and autumn (October) using excitation-emission matrix (EEM) spectra coupled with parallel factor (PARAFAC), EEM-PARAFAC modelling. The EEM-PARAFAC modelling results demonstrated that dissolved organic matter (DOM) in the Silin Reservoir waters was composed of three fluorescent components. These included terrestrial humic-like substances (C type) of terrestrial origin (component 1), microbial humic-like substances (M type) of phytoplankton origin (component 2), and protein-like or tryptophan-like or tyrosine-like (component 3) of phytoplankton origin. In addition, the terrestrial humic-like substances (C type) was identified from two fluorescence peaks (peak C at /=305-355/414-458 nm and peak A at / 245-270/414-458 nm) while the microbial humic-like substances (M type) was identified from peaks that included peak M at / 280-305/380-398 nm and peak A 230-235/380-417 nm. Similarly, protein-like or tryptophan-like or tyrosine-like components were also detected from two fluorescence peaks, including peak T 270-285/316-354 nm and peak T 225-230/316-354 nm. The fluorescence intensity of terrestrial humic-like substances gradually decreased in incoming waters to surface (0 m), deeper (20 m), and subsequently, in outflowing waters. This indicates the gradual degradation of the humic-like substances and their recalcitrant nature during water transport during the incoming-surface-deeper-outflowing water cycle in both summer and winter seasons by numerous environmental factors. These included photochemical, microbial, and dam barrier-affected physical processes. Conversely, from the fluorescence intensity results of microbial humic-like substances (M type), production or partial (in some cases complete) degradation in surface-deeper-outflowing waters, fluctuated. This suggests that microbial humic-like substances are autochthonously produced from phytoplankton, but are highly labile in response to photochemical, microbial, and dam barrier-affected physical processes. From the fluorescence intensity results of protein-like or tryptophan-like or tyrosine-like substances, it demonstrated that they were newly produced in surface (0 m) waters in the summer season, but in the winter season they were significantly produced in both surface and deeper waters of the reservoir, and then decreased in the outflowing waters. This suggests that protein-like or tryptophan-like or tyrosine-like substances are autochthonously produced by phytoplankton that simultaneously reproduced and then were degraded in surface and deeper waters by photochemical, microbial, and dam barrier-affected physical processes. These results therefore imply that the FDOM components identified by EEM-PARAFAC modelling are crucial to better understand the source characteristics of bulk DOM, its transformation mechanisms, and its the dynamics in a reservoir water system.