EAR-PF: Evaluating the relationship between physical heterogeneity and stable isotope fractionation factors during subsurface reactive transport

Jennifer Druhan博士被授予美国国家科学基金会地球科学博士后奖学金，以开展一项关于物理非均质性对测量和分析与地下反应输运相关的稳定同位素分馏的影响的联合实验和模型研究。虽然稳定同位素通常用于分析各种复杂的水文地球化学系统，但分馏模型通常需要简化假设，如均质、混合良好的反应性，导致对系统过程的错误描述。这项研究的实验方面将涉及一套中尺度流动柱反应器，填充了均匀和非均匀渗透率分布。这些色谱柱将被专门设计，以允许使用核中间成像技术精确地表征流动路径的异质性。模拟方面将涉及从核医学成像数据获得非均质渗透率分布的逆参数估计方法，以及通过这些渗透率分布进行分馏的正向地球化学反应输运模拟，以表征非均质溶质输运与观测分馏之间的关系。这项工作的目的是证明在均质和非均质系统中测量的有效分馏系数之间的差异，显示分级非均质性对这些测量的影响，并证明不断演变的渗透率场对同位素比率的时间影响。这项工作的结果将直接应用于分析近地表环境中的同位素数据集，研究范围从饮用水资源到污染物修复再到再生水储存。美国国家科学基金会支持的研究将在斯坦福大学地质和环境科学系进行。通过斯坦福大学涌动计划，这项研究的各个方面将被用来支持对地球科学本科生的指导。这项研究将进一步成为开发稳定同位素分馏的反应传输模型的短期课程的开创性范例。

Dr. Jennifer Druhan has been awarded an NSF Earth Science Postdoctoral Fellowship to carry out a combined experimental and modeling study of the influences of physical heterogeneity on the measurement and analysis of stable isotope fractionations associated with subsurface reactive transport. While stable isotopes are commonly used to analyze a wide variety of complex hydrogeochemical systems, models of fractionation routinely require simplifying assumptions such as homogeneous, well-mixed reactivity, leading to misrepresentation of system processes. The experimental aspect of this study will involve a suite of meso-scale, flow-through column reactors packed with homogeneous and heterogeneous permeability distributions. The columns will be designed specifically to allow precise characterization of flow-path heterogeneity using nuclear medial imaging techniques. The modeling aspect will involve both inverse parameter estimation methods to obtain heterogeneous permeability distributions from nuclear medical imaging data, and forward geochemical reactive transport simulations of fractionation through these permeability distributions to characterize the relationship between heterogeneous solute transport and observed fractionation. The goal of the work is to demonstrate the difference between effective fractionation factors measured in homogeneous and heterogeneous systems, to show the effects of hierarchical heterogeneity on these measurements, and to demonstrate the temporal influence of evolving permeability fields on isotopic ratios. Results of this work will have direct application to analysis of isotopic datasets in near-surface environments in studies ranging from drinking water resources to contaminant remediation to reclaimed water storage.The NSF supported research will be carried out at Stanford University in the Department of Geological and Environmental Sciences. Through the Stanford SURGE program aspects of the study will be leveraged to support mentorship of undergraduates in the earth sciences. The study will further serve as a seminal example in the development of a short course in reactive transport modeling of stable isotope fractionation.