Microbially Induced Anaerobic Oxidation of Magnetite to Maghemite in a Hydrocarbon‐Contaminated Aquifer
Microbially Induced Anaerobic Oxidation of Magnetite to Maghemite in a Hydrocarbon‐Contaminated Aquifer
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DOI：
10.1029/2021jg006560
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发表时间：
2022-04
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通讯作者：
L. Ohenhen;J. Feinberg;L. Slater;D. Ntarlagiannis;I. Cozzarelli;M. Rios-Sanchez;C. Isaacson;Alexis Stricker;E. Atekwana
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作者：
L. Ohenhen;J. Feinberg;L. Slater;D. Ntarlagiannis;I. Cozzarelli;M. Rios-Sanchez;C. Isaacson;Alexis Stricker;E. Atekwana
碳氢化合物污染场地中发生的铁矿物转化与碳氢化合物的生物降解有关。在美国明尼苏达州贝米吉附近的碳氢化合物污染场地，测量磁化率（MS）可用于监测与铁循环相关的碳氢化合物的自然衰减。然而，一个短暂的MS，以前观察到的网站，仍然知之甚少，铁矿物相作为反应物和产品与此MS扰动仍然在很大程度上是未知的。为了解决这些未知因素，我们获得了矿物磁性测量结果，包括磁滞回线，后场曲线，以及从现场取回的沉积物岩心样品和安装在含水层内的充满磁铁矿的矿物包的等温剩磁。我们的数据表明，岩心样品和磁铁矿包显示随着时间的推移，磁化强度下降，这种损失的磁化强度是伴随着增加的整体磁化率降低的平均晶粒尺寸和/或部分氧化。所有样品的低温磁力测定显示出与磁铁矿一致的行为，但羽流内的样品也显示出磁化的证据。通过扫描电子显微镜成像的颗粒表面上的收缩裂纹的发生支持这种解释。磁铁矿转化为磁赤铁矿通常发生在好氧条件下，在这里，我们建议磁赤铁矿化发生在缺氧部分的羽通过微生物介导的厌氧氧化。矿物溶解也发生在羽流内。在贝米吉场址的其他地区也发现了能够进行这种厌氧氧化的微生物，但还需要进行更多的微生物研究，以便将特定的厌氧铁氧化剂与这种磁化丧失联系起来。
Iron mineral transformations occurring in hydrocarbon‐contaminated sites are linked to the biodegradation of the hydrocarbons. At a hydrocarbon‐contaminated site near Bemidji, Minnesota, USA, measurements of magnetic susceptibility (MS) are useful for monitoring the natural attenuation of hydrocarbons related to iron cycling. However, a transient MS, previously observed at the site, remains poorly understood and the iron mineral phases acting as reactants and products associated with this MS perturbation remain largely unknown. To address these unknowns, we acquired mineral magnetism measurements, including hysteresis loops, backfield curves, and isothermal remanent magnetizations on sediment core samples retrieved from the site and magnetite‐filled mineral packets installed within the aquifer. Our data show that the core samples and magnetite packs display decreasing magnetization with time and that this loss in magnetization is accompanied by increasing bulk coercivity consistent with decreased average grain size and/or partial oxidation. Low‐temperature magnetometry on all samples displayed behavior consistent with magnetite, but samples within the plume also show evidence of maghemitization. This interpretation is supported by the occurrence of shrinkage cracks on the surface of the grains imaged via scanning electron microscopy. Magnetite transformation to maghemite typically occurs under oxic conditions, here, we propose that maghemitization occurs within the anoxic portions of the plume via microbially mediated anaerobic oxidation. Mineral dissolution also occurs within the plume. Microorganisms capable of such anaerobic oxidation have been identified within other areas at the Bemidji site, but additional microbiological studies are needed to link specific anaerobic iron oxidizers with this loss of magnetization.