Characteristics of different extractable organic matter in sediments and its hydrogeochemical significance: A case study of the typical study area in hetao basin
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摘要: 地下水系统中有机物（OM）特征和活性对于地下水化学特征的形成和演化起着十分重要的作用。将内蒙古河套盆地表层湖相沉积物按10 cm间隔采集，并对沉积有机质的性质及来源进行重点分析。测量了不同深度上不同岩性沉积物的色度、水溶性有机物（WEOM）和盐溶性有机物（SEOM）含量及其光谱学特性。结果显示，沉积物的色度（R530-520）与TOC含量呈现相反的变化趋势：色度值较大时，TOC含量反而较小。相对于细砂层，黏土层的色度值较低，但TOC含量较高。相同的沉积物中，SEOM含量高于WEOM，但WEOM更易迁移至地下水中。有机物的光谱指数表明，WEOM以微生物来源为主，而SEOM以陆源为主。通过三维荧光光谱分析发现，荧光强度和沉积物有机碳（SOC）含量呈正相关；黏土层沉积有机物荧光强度更高；WEOM和SEOM均含类腐殖质成分和类蛋白成分，但SEOM中腐殖质成分较高；类腐殖质是所研究的沉积物中OM最主要的存在形式。Abstract: Characteristics and reactivity of organic matter (OM) in groundwater systems play very important roles in the formation and evolution of groundwater chemical characteristics. In this study, 70 fluviolacustrine sediments were taken at 10 cm interval near the land surface in the Hetao Basin of Inner Mongolia to characterize sedimentary organic matter properties. The diffuse spectral reflectance of sediments, water soluble organic matter (WEOM) and salt soluble organic matter (SEOM) contents and their spectroscopic properties were measured. Results showed that diffuse spectral reflectance between 530 nm and 520 nm(R530-520) of sediments and TOC content showed the opposite trend: When the R530-520 value was higher, the TOC content was lower. In comparison with fine sand, clay layer had lower R530-520 values, but higher TOC contents. In the same sediment, contents of SEOM were higher than those of WEOM, but WEOM was easier to migrate into groundwater. The spectral index showed that WEOM possesses more biological/microbe-associated materials, but SEOM is representative of terrigenous materials.Excitation-emission matrix spectroscopy analysis showed that the fluorescence intensities were positively correlated with OC contents in sediments (SOC),which were high in clay layer. Moreover, both WEOM and SEOM had similar humic-like components and protein-like components, but the humic-like components in SEOM were higher than those in WEOM. Humic-like OM is considered to be the most important form in sedimentary OM in this study.
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Key words:
- sediment /
- groundwater /
- organic carbon /
- spectral index /
- excitation-emission matrix spectroscopy
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