Quantitative imaging of the 3-D distribution of cation adsorption sites in undisturbed soil
Quantitative imaging of the 3-D distribution of cation adsorption sites in undisturbed soil
复制标题
原状土壤中阳离子吸附位点 3-D 分布的定量成像
DOI：
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发表时间：
2017
期刊：
影响因子：
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通讯作者：
J. Koestel
中科院分区：
文献类型：
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作者：
H. Keck;B. Strobel;J. Gustafsson;J. Koestel
抽象的。几项研究表明，阳离子吸附位点的分布在毫米到厘米的尺度上是不均匀的。通常，在文献中已经报道了生物孔隙或聚集体涂层中更大浓度的卡斯。这种异质性对卡斯的可访问性有影响，并可能影响土壤系统模型的性能，假设空间均匀分布的CAS。在这项研究中，我们提出了一种新的方法来量化的丰度和3-D分布的卡斯在原状土壤中，允许调查CAS密度与距离的土壤大孔隙。我们使用钡离子作为造影剂的X线成像。Ba 2+对卡斯具有很高的吸附亲和力，被广泛用作衡量阳离子交换容量（CEC）的指标阳离子。八个土芯（约10立方厘米），从三个地点进行了采样，对比质地和有机质含量。在实验室中使用BaCl 2（0.3 mol L−1）使我们样品的卡斯与Ba 2+饱和。然后，用KCl（0.1 mol L-1）冲洗掉未与卡斯结合的Ba 2+离子。在此过程之前和之后，使用工业X射线扫描仪扫描样品。然后通过差分图像技术在3-D中可视化与卡斯结合的Ba 2+。将所得差异图像解释为仅描绘了与卡斯结合的Ba 2+。X射线图像衍生的CEC显着相关的结果，常用的醋酸铵法，以确定CEC在充分混合的样品。有机质丰富的样品的CEC似乎被系统高估，在粘土丰富的样品与有机质较少的CEC似乎被系统低估的情况下。结果表明，在我们的大多数样品中，卡斯的分布在空间上变化到毫米尺度。卡斯的位置与土壤大孔隙结构之间没有系统的关系。我们相信，这里提出的方法将有力地帮助更现实的土壤系统模型的发展。
Abstract. Several studies have shown that the distribution of cation adsorption sites (CASs) is patchy at a millimetre to centimetre scale. Often, larger concentrations of CASs in biopores or aggregate coatings have been reported in the literature. This heterogeneity has implications on the accessibility of CASs and may influence the performance of soil system models that assume a spatially homogeneous distribution of CASs. In this study, we present a new method to quantify the abundance and 3-D distribution of CASs in undisturbed soil that allows for investigating CAS densities with distance to the soil macropores. We used X-ray imaging with Ba2+ as a contrast agent. Ba2+ has a high adsorption affinity to CASs and is widely used as an index cation to measure the cation exchange capacity (CEC). Eight soil cores (approx. 10 cm3) were sampled from three locations with contrasting texture and organic matter contents. The CASs of our samples were saturated with Ba2+ in the laboratory using BaCl2 (0.3 mol L−1). Afterwards, KCl (0.1 mol L−1) was used to rinse out Ba2+ ions that were not bound to CASs. Before and after this process the samples were scanned using an industrial X-ray scanner. Ba2+ bound to CASs was then visualized in 3-D by the difference image technique. The resulting difference images were interpreted as depicting the Ba2+ bound to CASs only. The X-ray image-derived CEC correlated significantly with results of the commonly used ammonium acetate method to determine CEC in well-mixed samples. The CEC of organic-matter-rich samples seemed to be systematically overestimated and in the case of the clay-rich samples with less organic matter the CEC seemed to be systematically underestimated. The results showed that the distribution of the CASs varied spatially within most of our samples down to a millimetre scale. There was no systematic relation between the location of CASs and the soil macropore structure. We are convinced that the approach proposed here will strongly aid the development of more realistic soil system models.