三峡库区消落带土壤溶解性有机质溯源:基于氮/碳比值的线性双端元源负荷分析

土壤溶解性有机质(soil DOM)作为陆地系统天然有机质的重要组成部分,以其活跃的生物地球化学性质,在污染物的环境行为中扮演着极其重要的作用.而了解其来源和结构组成是进一步明确其"结构-反应活性"的关键和前提.本文以三峡库区消落带土壤DOM为研究对象,基于传统氮/碳比值(N/C)及衍生的双端元源负荷模型,讨论该溯源方法在分子水平上的合理性;同时采用光漂白试验,进一步讨论各样本反应活性与其源负荷的相关性.结果表明,N/C值和双端元线性混合模型值均表明土壤DOM具有"陆源"和"内源"的双重特性——这与其他高级分析技术溯源结果基本一致.这种传统溯源分析结果在分子水平上具有合理性,但仅仅反映DOM结构和来源在特定面相上的信息,只能证明库区土壤DOM属于"混合型来源",却无法提供分辨率更高的特定组分来源信息.另外,N/C元素比值及源负荷分别和光漂白动力学过程极显著相关,因此可作为较方便的指标,快速简单判断DOM的光化学反应活性.但在关注DOM本身生物地球化学的研究工作中,仍建议使用多重方法的比较分析,以便于提高单一解析方法的分辨率.

Use of the Nitrogen/Carbon Ratio (N/C) and Two End-Member Sources Mixing Model to Identify the Origins of Dissolved Organic Matter from Soils in the Water-Level Fluctuation Zones of the Three Gorges Reservoir

Soil dissolved organic matter (soil DOM) plays a crucial role in the environmental fate of pollutants because of its exceptional biogeochemical reactivity. Therefore, tracing the sources and understanding the properties of DOM through chemical characterization is important for clarifying the "structure-reactivity" of DOM in the environment. In this study, traditional elementary analysis methods including nitrogen/carbon ratio (N/C) determinations and derived two end-member source-loads mixing models were applied to soil DOM extracted from the water-level fluctuation zones of the Three Gorges Reservoir (TGR) area. The results were further compared to other characterization techniques that operate on the molecular scale (e. g., FTIR and analytical pyrolysis techniques). The ultimate objective was to assess the performance of N/C ratio and two end-member modeling for identifying the DOM sources. Additionally, a photo-bleaching kinetic experiment was conducted to test the correlation between DOM reactivity and its source-loadings. Results showed, based on the N/C ratio and mixing modeling, all soil DOM samples in the TGR area share "dual-source" characteristics, namely, allochthonousness (e. g., terrestrial) and autochthonousness (e. g., internal) attributes, which is in agreement with other advanced characterization tools. The traditional method results were comprehensible in light of the data from molecular techniques, but the information revealed only reflects certain aspects of DOM compositional characteristics. It can be concluded that the N/C ratio and mixing modeling can validate general sources of soil DOM, but not information about specific components. Meanwhile, the significant correlation between the photo-bleaching kinetic constant and N/C and source-loadings indicated that these two parameters can be used as rapid indicators to estimate soil DOM reactivity in photochemical processes. However, it should be emphasized that it remains essential to employ multiple characterization methods to investigate the biogeochemistry of soil DOM, so as to increase the characterization resolution with regard to the heterogeneity of DOM.