喀斯特湖泊-河流系统溶解性有机质光谱特征

为探索喀斯特湖泊-河流系统溶解性有机质(DOM)光谱特征空间格局,该研究以我国贵州红枫湖、百花湖和老马河为对象,分析了表层水体DOM紫外参数(SUVA₂₅₄、SUVA₂₈₀、S_275-295、S_350-400、S_R和E2/E3),利用三维荧光-平行因子(EEM-PARAFAC)解析DOM主要成分,同时基于荧光参数(HIX、FI、BIX和β：α)揭示其来源信息。该研究运用Spearman相关性分析及主成分分析(PCA)方法,揭示DOM参数的内在联系及重要组分贡献。结果显示,红枫湖、百花湖和老马河SUVA₂₅₄和SUVA₂₈₀值较低,而E2/E3、S_275-295和S_350-400值较高,说明芳香类成分占比较少且DOM整体分子量较小。水体DOM主要成分为:红枫湖/百花湖(C1:微生物代谢类腐殖质;C2:可见光范围腐殖质;C3:色氨酸),老马河(C1:色氨酸;C2:富里酸;C3:陆源类腐殖质)。水体BIX范围在0.77-1.12之间,说明生物源和陆源输入共同贡献DOM。红枫湖与百花湖FI值小于1.4,而老马河在1.4-1.9间,说明河流内源DOM贡献率高于湖泊。水体β：α值范围在0.73-1.10之间,说明新生DOM具有显著贡献。湖泊与河流HIX值低于4,表明水体腐殖化程度低。老马河HIX与S_R和S_275-295呈正相关(P ＜ 0.05)且与FI呈负相关(P ＜ 0.05),说明DOM腐殖化程度与分子大小和来源密切联系。芳香类DOM的同质性导致SUVA₂₅₄和SUVA₂₈₀相互耦合。研究发现新生DOM多具有生物降解性,表现为BIX和β：α强相关。相对于激流系统,湖泊具有更多的水力停留时间,这可能进一步促进内源微生物的代谢,导致生物驱动的有机质快速循环,因此不同DOM生物讯号相互耦合。研究阐明了喀斯特湖泊-河流系统DOM成分与来源特征,有望为研究全球碳循环过程提供数据支撑。

Unraveling spectral characteristics of dissolved organic matter in a karst lake-river system

Dissolved organic matter (DOM) response to biogeochemical processes in terrestrial and aquatic ecosystems, serves as a critical component for global and regional carbon cycling. However, spectral characteristics of aqueous DOM in region-specific sites, particularly in widely distributed karst waters are not well known. Here, we examined Hongfeng Lake, Baihua Lake, and Laoma River in Guizhou Province, China, to explore the composition and source of DOM in karst lake-river systems. We analyzed UV-vis parameters (SUVA₂₅₄, SUVA₂₈₀, S_275-295, S_350-400, S_R, and E2/E3) and three-dimensional fluorescence combined with parallel factor (PARAFAC), as well as fluorescence parameters (HIX, FI, BIX, and β：α) for DOM characterization. Spearman''s correlation analysis and principal component analysis (PCA) methods were employed for revealing inherent relationships among DOM parameters and primary variable contributions. The results showed that SUVA₂₅₄ and SUVA₂₈₀ values were low while E2/E3, S_275-295, and S_350-400 values were relatively high in the Hongfeng Lake, Baihua Lake, and Laomahe, indicating relatively limited proportion of aromatic components and low-molecular-size DOM. We found primary DOM components were: C1: microbially-derived humus, C2: visible-light humus and C3: tryptophan in the Hongfeng Lake and Baihua Lake, and yet C1: tryptophan, C2: fulvic acid, and C3: terrestrial humus in the Laoma River. The BIX ranged between 0.77 and 1.12, indicating that both biological and terrestrial inputs contributed to aquatic DOM. The FI values were lower than 1.4 in the lake Hongfeng and Baihua, while they varied from 1.4 to 1.9 in the Laoma River. This suggested the higher contributions of endogenous DOM in the river than that in the lakes. Aquatic β：α ranged between 0.73 and 1.10, indicating a significant contribution from newly produced DOM. The low HIX implied the limited humification in the studied karst waters. HIX was positively correlated with S_R and S_275-295 (P ＜ 0.05) and negatively correlated with FI (P ＜ 0.05), indicating that humification was constrained by DOM molecular size and sources. The homogeneity of aromatic DOM led to mutual couplings between SUVA₂₅₄ and SUVA₂₈₀. We highlighted that recently produced DOM was often biodegradable, which supported the strong correlations between BIX and β：α. The karst river exhibited more significant characteristics regarding endogenous contributions in comparison to the lakes, which might be attributing to rapid biogeochemical cycling within turbulent systems. Our results clarify the significance of terrigenous and biogenic signals in karst waters, upscaling the role of autochthonous and allochthonous carbon inputs for DOM dynamics. The study uncovers spectral characteristics of DOM composition and source in a karst lake-river system, which is expected to supplement useful datasets for global carbon cycling.