Dissolved organic matter (DOM) is the largest biologically available carbon pool in aquatic ecosystems and can mediate biogeochemical cycle processes. Its chemical nature and sources in marine environments and lakes have been extensively studied. However, DOM properties from river–reservoir systems in high altitude and severe cold climate regions remain unclear. In this study, the DOM components and sources in the upper “river–reservoir” system of the Yellow River were investigated using parallel factor analysis of fluorescence excitation–emission matrices. The factors influencing DOM florescence characteristics, especially the influence of cascade damming and frozen soil and freeze–thaw cycles, were explored. Our results demonstrated that the DOM fluorescence characteristics and sources of the river–reservoir system in the upper Yellow River had obvious temporal and spatial heterogeneity. Two humus-like substances (C1, C2) and one tryptophan-like substance (C3) were identified in the dry period. The fluorescence intensity of the cascade reservoir section (CR) was higher compared with the source region section (SR). External input and internal generation were the main sources of DOM, and the cascade reservoirs showed strong internal source characteristics. Two humus-like components (C1 and C2) were identified in the flood period, and the fluorescence intensity of the SR was higher compared with the CR. External input was the main source of DOM and the SR showed strong exogenous characteristics. The cascade reservoirs and seasonal freezing and thawing of frozen soil affected the fluorescence characteristics and sources of DOM. This study advances our knowledge of DOM florescence characteristics, sources, and influencing factors in river–reservoir systems in high altitude and severe cold climate regions.

中文翻译：

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黄河上游水库水系可溶性有机质分布特征及来源

溶解有机物 (DOM) 是水生生态系统中最大的生物可用碳库，可以调节生物地球化学循环过程。其在海洋环境和湖泊中的化学性质和来源已得到广泛研究。然而，高海拔和严寒气候地区河流水库系统的 DOM 特性仍不清楚。在这项研究中，使用荧光激发-发射矩阵的平行因子分析研究了黄河上游“河流-水库”系统中的 DOM 成分和来源。探索了影响DOM荧光特性的因素，特别是梯级筑坝和冻土以及冻融循环的影响。研究结果表明，黄河上游水库系统DOM荧光特征和来源具有明显的时空异质性。在干旱期鉴定出两种类腐殖质物质（C1、C2）和一种类色氨酸物质（C3）。与源区部分（SR）相比，级联储层部分（CR）的荧光强度更高。外输入内生是DOM的主要来源，梯级水库表现出强烈的内源特征。在洪水期间鉴定出两种类腐殖质成分（C1 和 C2），与 CR 相比，SR 的荧光强度更高。外部输入是DOM的主要来源，SR表现出很强的外生特征。梯级水库和冻土的季节性冻融影响DOM的荧光特性和来源。这项研究提高了我们对高海拔和严寒气候地区河流水库系统中 DOM 荧光特征、来源和影响因素的认识。