Collaborative Research: Investigating how transient electrical and magnetic signals relate to changes in recharge-driven redox state and iron mineral transformations

石油泄漏和/或原油管道破裂造成的碳氢化合物源区导致地球上储存可饮用地下水的含水层持续、长期的污染源。该项目通过推动理解碳氢化合物污染物在地球上的长期命运所需的科学来服务于国家利益。将使用传统上用于确定油层和矿藏位置的地球物理工具，以探索地球物理信号如何提供关于主要由地球上微生物驱动的污染物转化进展的诊断信息。这种对受石油污染地点的生物地球化学过程和地球物理信号之间随时间变化的联系的探索可能提供所需的知识，以便可靠地部署相对简单的地球物理测量系统，以监测漏油的长期命运。就像医学成像使用对人体的非侵入性传感一样，对污染物羽流的非侵入性地球物理传感最终可能被用来了解地下地球，而不需要钻探它。一种监测受人类影响的地下地球健康状况的非侵入性方法将限制人类和动物接触污染物，并消除侵入性钻探方法造成的污染物沿路径的有害传输。这项研究将由本科生与美国地质调查局(USGS)的政府科学家合作进行实地研究。该项目将吸引来自新泽西州北部城市经济贫困社区的少数族裔本科生参加。研究结果将通过举办与污染物羽流相关的地球物理信号研讨会与其他科学家和学生分享。过渡环境，如潜水和地下水位波动带(WTFZ)是生物地球化学热点，补给事件驱动的水文过程导致电子供体/受体混合物促进微生物新陈代谢。过渡环境中的水文-生物地球化学过程由于这些系统的时空和动态性质，利用水文、微生物和地球化学指标进行研究是具有挑战性的。在富含有机物质的污染地点，WTFZ内发生的地球化学和微生物过程/转变会产生磁化率(MS)和自电位(SP)电信号，这些电信号表明受到补给事件和水位变化的调控。对导致测量到的地球物理反应的生物地球化学因素的了解仍不完整，这是应用这些技术来调查野外水文生物地球化学过程所必需的。该项目将在一个高度特色化的地点进行跨学科研究，在那里可以获得数十年的水文、地球化学和微生物学数据，以解释引起地球物理特征的驱动机制。它将把本科教育与基础研究结合起来，以促进对这种生物地球物理特征的起源以及它们如何受到不同水文条件的调节的理解。将进行辅助实验室研究，以限制铁循环与WTFZ内的生物地球物理特征之间的联系。将获得数据集以解决下列假设：(1)瞬时磁化率剖面是由源区中水文驱动的铁循环引起的；[2)碳氢化合物源区磁化率的变化是由于最初存在于沉积物中的氢氧化铁的消耗引起的；[3)瞬时自电位特征与溶解或气相电子受体的再充电驱动的修改有关；[4]微生物介导的Fe(II)/Fe(III)氧化还原对通过源区的WTFZ驱动生物地理生物，从而造成异常的自电位剖面。假说将通过现场地球物理测量、悬浮在钻孔中的沉积物包的现场地球化学测量和WTFZ区域的实验室模拟来探索。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Hydrocarbon source zones resulting from oil spills and/or crude oil pipeline ruptures result in persistent, long-term source of contamination of the aquifers that store potable groundwater in the Earth. This project serves the national interest by advancing the science needed to understand the long-term fate of hydrocarbon contaminants in the Earth. Geophysical tools that have been traditionally implemented to locate oil reservoirs and mineral deposits will be used to explore how geophysical signals provide diagnostic information on the progress of contaminant transformations that are largely driven by microbes in the Earth. This exploration of the linkages between biogeochemical processes and geophysical signals over time at an oil contaminated site may provide the knowledge needed to reliably deploy relatively simple geophysical measurement systems to monitor the long-term fate of oil spills. In the same way that medical imaging uses non-invasive sensing of the human body, non-invasive geophysical sensing of contaminant plumes might ultimately be used to understand the subsurface Earth without the need to drill into it. A non-invasive approach to monitoring the health of the human-impacted subsurface Earth would limit exposure of humans and animals to contaminants and negate unwanted transport of contaminants along pathways caused by invasive drilling methods. The research will be performed by undergraduate students performing field-based research in collaboration with government scientists from the United States Geological Survey (USGS). The project will engage minority undergraduate geoscience students from urban, economically disadvantaged neighborhoods in northern New Jersey. Results of the research will be shared with other scientists and students by running a workshop on geophysical signals associated with contaminant plumes. Transitional environments such as hyporheic and water table fluctuation zones (WTFZ) are biogeochemical hotspots where hydrologic processes driven by recharge events cause electron donor/acceptor mixtures that enhance microbial metabolism. Hydro-biogeochemical processes in transitional environments are challenging to study using hydrological, microbial and geochemical proxies due to the spatio-temporal and dynamic nature of these systems. Geochemical and microbial processes/transformations occurring within the WTFZ at organic-rich contaminated sites give rise to magnetic susceptibility (MS) and self potential (SP) electrical signals that show evidence of being regulated by recharge events and changes in water level. Understanding of the biogeochemical factors resulting in the measured geophysical responses, as needed to apply these techniques to investigate hydro-biogeochemical processes at field sites, remains incomplete. This project will pursue interdisciplinary research at a highly characterized site where decades of hydrological, geochemical and microbiological data are available to interpret the driving mechanisms causing geophysical signatures. It will integrate undergraduate education with basic research to advance understanding of the origins of such biogeophysical signatures and how they are regulated by variable hydrologic conditions. Supporting laboratory studies will be performed to constrain the linkages between iron cycling and biogeophysical signatures within the WTFZ. Datasets will be acquired to address the following hypotheses: [1] Transient magnetic susceptibility profiles result from hydrologically-driven iron cycling in the source zone; [2] Magnetic susceptibility changes in hydrocarbon source zones result from the consumption of iron-oxyhydroxides initially present on the sediments; [3] Transient self potential signatures are associated with recharge-driven modifications of dissolved or gas phase electron acceptors; [4] A microbial-mediated Fe(II)/Fe(III) redox couple drives a biogeobattery causing an anomalous self potential profile through the WTFZ in the source zone. Hypotheses will be explored by a combination of field geophysical measurements, in situ geochemical measurements on sediment packets suspended in boreholes and laboratory simulations of the WTFZ zone.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.