Collaborative Research: Unraveling the link between water ages and silicate weathering rates at the catchment scale

水和矿物之间的相互作用是一个基本的过程，它塑造和记录了对风景的记忆，产生了维持生态系统的水质和养分，并在更长的时间尺度上吸收了大气中的二氧化碳。在分水岭中，水通过雨雪被注入到风景中，在那里它沿着地下的各种路径开始它的旅程。在这条路上，水与矿物质相遇并交换，结合了从固体中释放出来的化学物质，并在一个称为风化的过程中将它们转化为其他形式。最终，具有独特化学特征的水从系统中被冲到附近的溪流和地下水泉水中。传统的看法是，水与周围的地下接触的时间越长，它的化学演化就越严重。在这一框架下，在集水区观察到的风化量应与地下水年龄有着千丝万缕的联系。从历史上看，这种关系很难完全评估。该项目将使用现代地球化学工具并结合先进的建模方法，以促进我们对位于加利福尼亚州内华达山脉中部的山丘集水区Sagehen Creek盆地地下水年龄与风化通量之间关系的理解。这项合作研究工作将支持两名早期职业科学家，一名博士生和一名现场技术人员，并为本科生研究提供机会。研究人员将与成熟的地球科学教育工作者合作，推出一套教育产品和倡议，让更广泛的公众、高中生和教师参与水文学和水质主题。这项研究旨在通过水文和地球化学相结合的方法，在流域尺度上更好地描述地下水年龄与硅酸盐风化速率之间的关系。由于缓慢的反应动力学，硅酸盐风化反应与集水区水文学是唯一耦合的；因此，溶质的产生本质上取决于流体暴露在矿物中的时间。该项目将开发和利用一个新的全面的水龄(氯氟化碳、六氟化硫和35S)和风化(δ30Si、δ44Ca和Ge/Si)示踪数据集，以提供耦合的2D物理传输水文和同位素启用的多组分反应传输模型。这项研究将在Sagehen Creek盆地进行，这是一个融雪驱动、火成岩、对气候敏感的山地分水岭。Sagehen是一个被广泛研究的地点，先前的几项研究表明，测量的风化衍生溶质通量与地下水停留时间之间存在相关性。这种水文和地球化学相结合的方法将为流体传输时间和硅酸盐风化之间的协同关系提供前所未有的洞察力。研究人员计划生成动态的、不断演变的水的传输时间分布，以响应季节性和事件的强迫，并通过纳入“快”/浅和“慢”/深的地下水成分。这项研究还提供了一个机会，以评估对不同反应途径敏感的稳定同位素和微量元素示踪剂的效用，并量化反应程度如何作为“反应时钟”。这些发现将为关键地带科学中与流域水文地球化学对气候变化的反应有关的长期存在的问题提供洞察。这项研究由地球科学地球生物学和低温地球化学项目和水文科学项目共同资助。该奖项反映了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。

The interaction between water and minerals is a fundamental process that shapes and records memories of landscapes, generates water quality and nutrients to sustain ecosystems, and draws down atmospheric CO2 over longer timescales. In watersheds, water is fed into the landscape through rain and snow where it starts its journey along various paths in the subsurface. Along the path, water encounters and exchanges with minerals, incorporating chemicals liberated from the solids and transforming them into other forms in a process termed weathering. Eventually the water with its unique chemical signature is flushed from the system into nearby streams and groundwater springs. The conventional wisdom is that the longer water spends in contact with the surrounding subsurface, the more chemically evolved it becomes. Under this framework, the amount of weathering observed in a catchment should be inextricably linked with groundwater ages. Historically, this relationship has been difficult to fully evaluate. This project will use modern geochemical tools in tandem with advanced modeling approaches to advance our understanding of the relationship between groundwater ages and weathering fluxes in a montane catchment, Sagehen Creek Basin, located in the Central Sierra Nevada mountains in California. This collaborative research effort will support two early career scientists, one PhD student, a field technician, and provide opportunities for undergraduate research. Researchers will collaborate with established Earth Science educators to launch a suite of educational products and initiatives to engage the broader public, high school students and instructors on hydrology and water quality themes. This research aims to better characterize the relationship between groundwater ages and silicate weathering rates at the catchment-scale through a combined hydrologic and geochemical approach. Silicate weathering reactions are uniquely coupled to catchment hydrology due to slow reaction kinetics; thus, solute generation is inherently dependent on the time fluids spend exposed to minerals. The project will develop and leverage a new, comprehensive water age (CFC, SF6, and 35S) and weathering (δ30Si, δ44Ca, and Ge/Si) tracer dataset to inform a coupled 2D physical transport hydrologic and isotope-enabled, multicomponent reactive transport model. The study will be conducted at Sagehen Creek Basin, a snowmelt driven, igneous, montane watershed sensitive to climatic. Sagehen is a widely studied site with several prior studies demonstrating a correlation between measured weathering-derived solute fluxes and groundwater residence times. This hybrid hydrological and geochemical approach will provide unprecedented insight into the synergistic relationship between fluid transit time and silicate weathering. The researchers plan to generate dynamic, continually evolving transit time distributions for water in response to both seasonal and event forcing, and through the incorporation of “fast”/shallow and “slow”/deeper groundwater components. This research further provides an opportunity to evaluate the utility of stable isotopes and trace element tracers that are sensitive to distinct reaction pathways, and to quantify how the extent of reactions can serve as “reaction clocks”. Findings will provide insight into persistent questions in critical zone science related to watershed hydrogeochemical response to climate change. This research is co-funded by the Division of Earth Sciences Geobiology and Low-Temperature Geochemistry Program and Hydrologic Sciences Program.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.