CAREER: Unlocking the Isotopic Signatures of Weathering Recorded in Rivers Through Isotope-Enabled Reactive Transport

水通过固体地球最浅层的渗透对维持地球上的生命至关重要。土壤中的水分灌溉着我们种植的作物，维持着自然生态系统。深入地下的水补充了含水层，并为溪流和河流提供了基流。这种通过浅层地球的运输也引入了水作为一种反应剂，能够风化构成地壳的矿物质，允许将岩石转化为土壤的化学转化，并设置水资源的化学特征。因此，水是这个“关键地带”的一个积分，即我们生活和获取资源的地球表面。这种重要的变化在很大程度上是无法直接研究的，因为它们发生在我们脚下的近地表。因此，我们依靠描述流体通过临界区域的速率和路径的模型，再加上水、矿物质和生命之间发生的化学反应，来预测在我们无法直接观察的地方会发生什么。然后，这些模型与更容易获得的样本进行核对，这些样本通常使用排水的溪流和河流的化学成分。利用新型仪器和模型开发，该项目将首次直接验证这些基于从土壤到河流过渡过程中收集的流体和固体的反应性输运模型。本研究的广泛影响包括改进水质化学特征和临界带功能的预测模型。开发和部署这种模型的能力对流域管理和关键带科学的进步至关重要。为了实现这一目标，该项目将创建一个开放访问的在线培训平台，旨在教育下一代地球科学家开发最先进的反应传输模型。教学模块将作为NSF-RCN奖的一部分部署，并将具有ada兼容的网页设计，具有自我指导和课堂集成选项。该资源将促进下一代定量模型的扩大使用和公平可得性，并促进全球关键区社区的国际合作。关键带风化剖面中流体输运与化学反应性紧密耦合的预测模型，在很大程度上仍然是通过容易获得的观测结果来验证的，比如以泉水和基流的形式出现的流体。这些流体排水景观的综合特征提供了测试正演模型的重要手段，现在越来越重视使用河流稳定同位素比率（例如，<s:1> 7Li、30Si、27Mg、44Ca），因为它们对化学风化的特定成分具有高度敏感性。将这些有前途的工具集成到反应输运模拟中，可以为化学和流体流动耦合的高保真预测模型提供关键。这一建议将为实现这一目标产生三个主要进展：(1)溶质同位素特征作为流体旅行时间的函数的定量解释；(2)入渗-排放间风化带同位素特征验证；(3)利用流域内河流同位素比值记录的风化过程预测模型。这将通过利用一系列实验室柱实验来实现，这些实验旨在支持模型的开发，并反过来应用于一种新的现场规模的仪器功能，该功能允许在关键区域的部分饱和部分直接收集流体样品，在该区域流体通过风化层排出，然后作为基流进入溪流。这项工作的结果将测试一组假设，这些假设将理论与来自化学风化的溶质同位素比率的观察联系起来。该奖项反映了美国国家科学基金会的法定使命，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。

The percolation of water through the shallowest layers of the solid Earth is vital to sustaining life on this planet. Moisture delivered to soil irrigates the crops we grow and sustains natural ecosystems. Water that reaches further into the subsurface recharges aquifers and supplies the baseflow to streams and rivers. This transit through the shallow Earth also introduces water as a reactive agent capable of weathering the minerals that compose the crust, allowing chemical transformations that convert rock to soil and set the chemical signature of water resources. Thus, water is an integrator of this “critical zone”, i.e., the surface of the Earth where we live and draw resources. Such vital transformations are largely hidden from direct study because they occur below our feet in the near surface. Thus, we rely upon models that describe the rates and pathways of fluid drainage through the critical zone, coupled to the chemical reactions that occur between water, minerals and life, to predict what takes place where we cannot make direct observations. These models are then checked against more accessible samples often using the chemistry of streams and rivers which drain watersheds. Using novel instrumentation and model development, this project will offer the first direct validation of these reactive transport models based on fluids and solids collected within the transition from soil to stream. The broader impacts of this study include the improvement of predictive models for the chemical signatures of water quality and critical zone functioning. The capability to develop and deploy such models is vital to the advancement of watershed management and critical zone science. In pursuit of this goal, the project will create an open access online training platform designed to educate the next generation of Earth scientists in the development of state-of-the-art reactive transport models. The teaching modules will be deployed as part of an NSF-RCN award and will feature ADA-compliant web design with both self-guided and classroom integration options. This resource will foster the expanded use and equitable availability of next generation quantitative models and promote international collaborations across the global critical zone community.Predictive models for the tight coupling between fluid transport and chemical reactivity in critical zone weathering profiles remain largely validated against easily accessible observations such as the fluids that emerge as spring water and baseflow to streams and rivers. These integrated signatures of fluid draining landscapes offer a vital means of testing forward models and an increasing emphasis is now being placed on the use of riverine stable isotope ratios (e.g., 7Li, 30Si, 27Mg, 44Ca) for their exquisite sensitivity to specific components of chemical weathering. Integration of these promising tools into reactive transport simulations could hold the key to high fidelity predictive models for the coupling of chemistry and fluid flow draining intact weathering profiles. This proposal will generate three major advancements towards this goal: (1) quantitative interpretation of solute isotope signatures as a function of fluid travel time; (2) validation of isotope signatures in the zone of weathering between infiltration and discharge; and (3) predictive models for the weathering processes recorded by the isotope ratios of rivers draining watersheds. This will be accomplished through leveraging of a series of laboratory column experiments designed to support model development and in turn application to a novel field-scale instrumentation capability which allows direct collection of fluid samples in the partially saturated section of the critical zone where fluid drains through regolith before emerging as the baseflow to streams. The results of this work will test a set of hypotheses that link theory to observations of isotope ratios in the solutes derived from chemical weathering.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.