思林水库荧光溶解性有机质的特征、来源及其转化动力学

利用三维荧光光谱(EEM)结合平行因子分析(PARAFAC),研究了思林水库冬季(1月)、春季(4月)、夏季(6月)和秋季(10月)上游入库水体、库区表层水(0 m)、库区深层水(20 m)、出库水体的荧光溶解性有机质(FDOM)不同组分的特征、来源及其转化动力学.结果表明,思林水库的溶解性有机质由3种荧光组分组成,分别是:陆源类腐殖质(C类,C1)、浮游植物源的微生物类腐殖质(M类,C2)和浮游植物源的类蛋白或类色氨酸或类酪氨酸(C3).其中陆源类腐殖质的荧光强度随着入库水、库区表层水、库区深层水和出库水逐渐减少,这表明由于光化学作用、微生物作用、大坝拦截效应等环境因素的影响,类腐殖质随着水体由入库向出库的流动而逐渐降解.相反,微生物类腐殖质(M类)的荧光强度结果表明,在入库-出库过程中,微生物类腐殖质处于产生及部分或完全降解的波动中,这表明微生物类腐殖质是浮游植物的原生产物,并且对于光化学作用、微生物作用和大坝拦截效应有很强的不稳定性.类蛋白或类色氨酸或类酪氨酸主要新产生于夏季和秋季的表层水体中,在冬季和春季表层和深层水体中也有产生;并在出库过程中逐渐减少.这表明类蛋白或类色氨酸或类酪氨酸是浮游植物的原生产物;并且它们受到光化学作用、微生物作用和大坝拦截效应的共同影响,在表层和深层水中生成和降解.因此,这些结果意味着通过平行因子分析确定的荧光溶解性有机质组分的方法,对于更好地理解溶解性有机质在水库水体的转化动力学机制至关重要.

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 E_x/E_m=305-355/414-458 nm and peak A at E_x/E_m 245-270/414-458 nm) while the microbial humic-like substances (M type) was identified from peaks that included peak M at E_x/E_m 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_uv 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.