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

石油溢漏和/或原油管道破裂造成的碳氢化合物源区是地球上储存可饮用地下水的含水层的持久、长期污染源。该项目通过推进了解地球碳氢化合物污染物长期命运所需的科学来服务于国家利益。传统上用于定位油藏和矿床的地球物理工具将用于探索地球物理信号如何提供关于污染物转化进展的诊断信息，这些污染物转化主要由地球上的微生物驱动。这种对石油污染场地的地球化学过程和地球物理信号之间的联系的探索，可以提供可靠地部署相对简单的地球物理测量系统以监测石油泄漏的长期命运所需的知识。就像医学成像使用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感测最终可能用于了解地下地球，而无需钻入地下。受影响的地下地球将限制人类和动物暴露于污染物，并消除污染物沿侵入性污染物造成的沿着路径的不必要的运输。钻井方法该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。该项目将吸引来自北方新泽西城市经济贫困社区的少数民族地球科学本科生。研究结果将通过举办与污染物羽流相关的地球物理信号讲习班与其他科学家和学生分享。过渡环境，如潜流和地下水位波动区（WTFZ）是生物地球化学热点，其中由补给事件驱动的水文过程导致电子供体/受体混合物，增强微生物代谢。过渡环境中的水文地球化学过程是具有挑战性的研究，利用水文，微生物和地球化学替代品，由于这些系统的时空和动态的性质。地球化学和微生物的过程/转换发生在富含有机物的污染场地内的WTFZ引起磁化率（MS）和自电位（SP）的电信号，显示出被调节的补给事件和水位变化的证据。了解地球化学因素导致测量的地球物理响应，需要应用这些技术来调查水文地球化学过程在现场，仍然不完整。该项目将在一个高度特征化的地点进行跨学科研究，那里有数十年的水文、地球化学和微生物数据，可用于解释造成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，以促进对这种地球物理特征的起源以及它们如何受到可变水文条件的调节的理解。将进行支持性实验室研究，以限制WTFZ内铁循环和地球物理特征之间的联系。将获取数据集以解决以下假设：[1]瞬变磁化率剖面是由源区水文驱动的铁循环造成的; [2]烃源区磁化率变化是由沉积物上最初存在的铁氢氧化物消耗造成的;[3]瞬态自电位特征与溶解或气相电子受体的再充电驱动修改有关;[4]微生物介导的Fe（II）/Fe（III）氧化还原电对驱动微电池，导致源区WTFZ的异常自电位分布。 将通过实地地球物理测量、钻孔中悬浮沉积物包的现场地球化学测量和WTFZ区的实验室模拟相结合来探索假设。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值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.