Spectroscopic (XANES/XRF) characterization of contaminant manganese cycling in a temperate watershed
Spectroscopic (XANES/XRF) characterization of contaminant manganese cycling in a temperate watershed
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DOI：
10.1007/s10533-014-0018-7
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发表时间：
2014-08
期刊：
影响因子：
4
通讯作者：
E. Herndon;C. Martínez;S. Brantley
中科院分区：
文献类型：
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作者：
E. Herndon;C. Martínez;S. Brantley
由于人类活动的投入，全球许多土壤都受到金属污染；然而，将这些金属保留在土壤中或将其冲入河流系统的长期过程仍不清楚。美国宾夕法尼亚州中部的水源集水区萨斯奎哈纳/页岩山关键区观测站的土壤由于过去工业来源的大气沉积而富含锰。为了研究锰如何保留在流域中，我们使用 X 射线荧光和 X 射线吸收近边缘结构光谱评估了土壤-植物系统中锰的空间分布和形态。地表附近的风化土壤富含无定形和结晶的锰（III/IV）氧化物，可能分别来自生物降水和大气沉积。相比之下，靠近土壤-基岩界面的矿质土壤中，粘土中含有 Mn(II)，并且当 Mn(II) 从母页岩中浸出并氧化时，形成结晶 Mn(III/IV) 氧化物。根、茎和叶组织主要由有机结合的和含水的 Mn(II) 组成；然而，一小部分叶面锰以有机结合的 Mn(III) 形式浓缩在黑斑中，这表明锰具有毒性。在叶和根的分解过程中，植被中储存的可溶性锰（II）被迅速氧化并以混合价锰氧化物的形式固定。我们认为，某些植物物种对锰的大量吸收，加上有机物分解过程中锰的快速氧化，有助于在土壤中长期保留，并可能减缓流域中锰污染的清除。
Many soils around the globe are contaminated with metals due to inputs from anthropogenic activities; however, the long-term processes that retain these metals in soils or flush them into river systems remain unclear. Soils at the Susquehanna/Shale Hills Critical Zone Observatory, a headwater catchment in central Pennsylvania, USA, are enriched in manganese due to past atmospheric deposition from industrial sources. To investigate how Mn is retained in the catchment, we evaluated the spatial distribution and speciation of Mn in the soil–plant system using X-ray fluorescence and X-ray Absorption Near Edge Structure spectroscopies. Weathered soils near the land surface were enriched in both amorphous and crystalline Mn(III/IV)-oxides, presumably derived from biogenic precipitation and atmospheric deposition, respectively. In contrast, mineral soils near the soil–bedrock interface contained Mn(II) in clays and crystalline Mn(III/IV)-oxides that formed as Mn(II) was leached from the parent shale and oxidized. Roots, stems, and foliar tissue were dominated by organic-bound and aqueous Mn(II); however, a small portion of foliar Mn was concentrated as organic-bound Mn(III) in dark spots that denote Mn toxicity. During decomposition of leaves and roots, soluble Mn(II) stored in vegetation was rapidly oxidized and immobilized as mixed-valence Mn-oxides. We propose that considerable uptake of Mn by certain plant species combined with rapid oxidation of Mn during organic matter decomposition contributes to long-term retention in soils and may slow removal of Mn contamination from watersheds.