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

Jennifer Druhan博士获得了美国国家科学基金会地球科学博士后奖学金，开展了一项物理非均质性对与地下反应输运相关的稳定同位素分块测量和分析的影响的实验和建模研究。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，例如均匀、混合良好的反应性，从而导致系统过程的错误描述。本研究的实验方面将涉及一套具有均匀和非均匀渗透率分布的中尺度，流经塔式反应器。该柱将专门设计，以允许使用核医学成像技术的流动路径异质性的精确表征。建模方面将涉及逆参数估计方法，从核医学成像数据中获得非均质渗透率分布，以及通过这些渗透率分布对分馏进行地球化学反应性输运模拟，以表征非均质溶质输运与观察分馏之间的关系。这项工作的目标是证明在均质和非均质系统中测量的有效分馏因子之间的差异，显示分层非均质对这些测量的影响，并证明不断变化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从饮用水资源到污染物修复到再生水储存等近地表环境中同位素数据集的分析。这项由美国国家科学基金会资助的研究将在斯坦福大学地质与环境科学系进行。通过斯坦福大学的SURGE项目，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。该研究将进一步为稳定同位素分馏反应输运模型的短期课程发展提供一个开创性的例子。

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.