Redox controls on arsenic enrichment and release from aquifer sediments in central Yangtze River Basin
Redox controls on arsenic enrichment and release from aquifer sediments in central Yangtze River Basin
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DOI：
10.1016/j.gca.2017.01.035
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发表时间：
2017-05
影响因子：
5
通讯作者：
Michael V. Schaefer;Xinxin Guo;Y. Gan;S. Benner;Aron M. Griffin;C. Gorski;Yan-xin Wang;S. Fendorf-S.
中科院分区：
文献类型：
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作者：
Michael V. Schaefer;Xinxin Guo;Y. Gan;S. Benner;Aron M. Griffin;C. Gorski;Yan-xin Wang;S. Fendorf-S.
目前，亚洲有超过1亿人暴露在砷(As)浓度超过世界卫生组织标准10μg/L−1的地下水中。最近有报道称，长江中部流域的地下水受到砷污染，但控制砷浓度的过程尚未解决。我们研究了长江内陆沉积盆地江汉平原内控制砷的水文和地球化学因素，那里的砷浓度表现出强烈的季节性变化，受地表和地下水混合的驱动(Schaefer等人，2016)。水文波动改变了含水层中的氧化还原条件，导致砷/铁还原和氧化之间的振荡。在这里，我们研究了固体和水相铁和砷的深度分布，并通过一系列的实验室操作，限制了控制地下水砷浓度季节性变化的生物地球化学过程。在表层以下∼20米处的沉积物培养中，固相砷浓度超过100m g/kg−1，未经修饰和葡萄糖修饰的沉积物样品都会导致砷释放到水相。相反，来自其他深度的沉积物批量培养导致As的释放有限。富集区中的固相砷相对被氧化，但在短时间内可能被还原。在富砷带以下的沉积物中，葡萄糖修饰导致了砷的还原，但砷向水相的释放受到随后形成的硫化砷矿物的限制。江汉平原含水层中埋藏的沉积砷与地下有机碳的厌氧微生物呼吸作用相结合，导致砷快速释放到地下水中。在∼20米深的沉积物中释放的砷足以解释整个含水层的砷浓度，并提供了一种机制来解释水文变化如何导致地下水中砷浓度的季节性变化。
More than 100 million people in Asia are presently exposed to groundwater with arsenic (As) concentrations exceeding the World Health Organization standard of 10 μg L−1. Arsenic contaminated groundwater within basins of the central portion of the Yangtze River has recently been reported, but the processes controlling arsenic concentrations have yet to be resolved. We examined the hydrologic and geochemical factors controlling arsenic within the Jianghan Plain, an inland sedimentary basin of the Yangtze River, where arsenic concentrations exhibit strong seasonal variability driven by surface and groundwater mixing (Schaefer et al., 2016). Hydrologic fluctuations alter redox conditions in the aquifer, leading to oscillations between arsenic/iron reduction and oxidation. Here we investigate the depth-distribution of solid and aqueous phase iron and arsenic species and, through a series of laboratory manipulations, constrain the biogeochemical processes controlling seasonal changes in groundwater arsenic concentrations. In sediment incubations from ∼20 m below the surface, where solid-phase arsenic concentrations exceed 100 mg kg−1, both unamended and glucose-amended sediment samples result in arsenic release to the aqueous phase.In situcarbon was capable of promoting As release in the sediment. In contrast, sediment batch incubations from other depths resulted in limited As release. Solid phase arsenic in the enriched zone was relatively oxidized but may become reduced over short time periods. In sediments below the As-enriched zone, glucose amendment resulted in arsenic reduction, but arsenic release to the aqueous phase was restricted by the subsequent formation of arsenic sulfide minerals. Buried sedimentary arsenic coupled with anaerobic microbial respiration of subsurface organic carbon within the Jianghan Plain aquifer leads to rapid release of As to groundwater. Arsenic release from sediments at ∼20 m depth is sufficient to explain arsenic concentrations throughout the aquifer, and provides a mechanism to explain how shifts in hydrology result in seasonally variable arsenic concentrations in groundwater.