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The concentration and size distribution of iron-rich colloids in pore waters are related to soil organic matter content and pore water calcium concentration
European Journal of Soil Science ( IF 4.2 ) Pub Date : 2021-03-11 , DOI: 10.1111/ejss.13104
Claudia Moens 1 , Daniela Montalvo 1 , Erik Smolders 1
Affiliation  

Iron (Fe)-rich colloids in the environment have a high surface reactivity and facilitate transport of oxyanions and trace metal cations in soil. This study was set up to help identify the soil properties that might affect the concentrations of colloidal Fe and its size distribution in pore waters of soils. The pore water was isolated by centrifugation from a collection of 97 topsoils with contrasting properties and land use. The total Fe concentration in the pore waters ranged between 0.2 and 26 μM (10th–90th percentile) and was largest at low soil solution calcium (Ca) and high dissolved organic carbon (DOC), indicating that enhanced colloidal stability determines total Fe in solution. The colloidal size distribution (<100 nm) of Fe in the pore waters of 11 soils was determined with flow field flow fractionation (FlFFF-UV-ICP-MS), which yielded three different fractions that varied strikingly among soils. The smallest fraction (<5 nm) of Fe co-eluted with high DOC and copper (Cu), suggesting mononuclear Fe-organic carbon (OC) complexes. This fraction increased with an increasing DOC/Fe ratio in pore waters. The 5–50-nm fraction of Fe prevailed in soils with >3.5% organic carbon (%OC), whereas the 50–100-nm fraction was dominant in soils with low %OC content. This suggests that natural organic matter inhibits crystallization and growth of mineral Fe particles. The elemental ratios of mineral colloids (>5 nm) indicated the presence of clay minerals and Fe oxyhydroxides, which was confirmed by scanning electron microscopy (SEM) analysis. This study thus identified soil %OC and Ca in soil solution as the dominant factors predicting both the concentration and size of pore water Fe colloids, with the smallest and, potentially, most mobile Fe colloids occurring in OC-rich soils.

中文翻译:

孔隙水中富铁胶体的浓度和粒径分布与土壤有机质含量和孔隙水钙浓度有关

环境中富含铁 (Fe) 的胶体具有高表面反应性,并促进土壤中氧阴离子和痕量金属阳离子的运输。本研究旨在帮助确定可能影响胶体 Fe 浓度及其在土壤孔隙水中的粒径分布的土壤特性。孔隙水是通过离心从具有对比性质和土地用途的 97 种表土中分离出来的。孔隙水中的总 Fe 浓度范围在 0.2 到 26 μM(第 10-90 个百分位数)之间,并且在低土壤溶液钙 (Ca) 和高溶解有机碳 (DOC) 时最大,表明增强的胶体稳定性决定了溶液中的总 Fe . 用流场流分馏法 (FlFFF-UV-ICP-MS) 测定了 11 种土壤孔隙水中 Fe 的胶体粒径分布 (<100 nm),这产生了三种不同的部分,这些部分在土壤中差异显着。最小部分 (<5 nm) 的 Fe 与高 DOC 和铜 (Cu) 共洗脱,表明是单核 Fe-有机碳 (OC) 复合物。该比例随着孔隙水中 DOC/Fe 比的增加而增加。5-50 nm 的 Fe 在有机碳 (%OC)>3.5% 的土壤中占主导地位,而 50-100-nm 的部分在有机碳含量低的土壤中占主导地位。这表明天然有机物抑制了矿物铁颗粒的结晶和生长。矿物胶体的元素比 (>5 nm) 表明存在粘土矿物和 Fe 羟基氧化物,这通过扫描电子显微镜 (SEM) 分析得到证实。
更新日期:2021-03-11
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