CAREER: Balancing the global alkalinity cycle by improving models of river chemistry

今天在河流中流动的水主要是由过去落下的雨水组成的，这些雨水在到达河道之前进入地下。这一凌日所花费的时间也是化学反应发生的时间。同时，雨水通过分水岭的确切路径--无论是穿过浅层土壤还是深层破裂的基岩--影响着发生的反应和反应的速度。因此，对河水化学的观测可以用模型来同样好地描述，这些模型将所有的变化归因于流动路径或流速的变化。这种模棱两可是有问题的，因为气候变化对水资源的预测影响是不同的，这取决于管理流动和反应的确切过程。为了提供对河水化学控制的新见解，该项目将开发新的方法来分析化学随时间的变化，以分离流动路径和流速的影响。该项目将通过工程设计课程、实习和关于当地水质问题的公共宣传来吸引本科生。这项工作将利用时间序列数据的信息内容来限制地下水传输和溶质获取的耦合时间尺度。为了避免过去工作中的一些假设，将使用非参数方法来推断地球化学动力学和溶质生成机制。在经过二维数值和模拟实验的验证后，该分析方法将用于阐明临界区结构在气候风化反馈中的作用，并解释微量元素和同位素替代物的非线性行为，以改进混合模型。这些应用的结果将用于对风化过程及其对行星宜居性的影响的新的全球分析，以及比较陆地和海洋系统的时间尺度不可知论框架。为了降低收集时间序列数据的门槛，本科生工程设计团队将开发一种专门设计的自动取样器。为了帮助更多的本科生参与地球科学研究，该项目将开发一门关于当地水质问题的新的外展课程。该项目由水文科学和地球生物学与低温地球化学项目共同资助。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 water flowing in a river today is largely composed of rainwater that fell in the past and traveled underground before arriving at the river channel. The amount of time this transit takes is also the amount of time available for chemical reaction to occur. At the same time, the exact path that rain takes through watersheds - whether through shallow soils or deep, fractured bedrock - influences which reactions occur and at what rates. Consequently, observations of river water chemistry can be described equally well by models that attribute all variation to changes in either flow paths or flow rates. This ambiguity is problematic as the predicted effects of climate change on water resources are different depending upon the exact processes governing flow and reaction. To provide new insights into the controls on river water chemistry, this project will develop new approaches for analyzing variations in chemistry over time to separate the effects of flow paths from flow rates. The project will engage undergraduate students through an engineering design course, internships, and public outreach on local water quality issues.This work will leverage the information content of time-series data to constrain the coupled timescales of subsurface water transit and solute acquisition. To avoid some of the assumptions embedded in past work, non-parametric approaches will be used to infer geochemical kinetics and solute generation mechanisms. After being validated against 2-D numerical and analog experiments, the analysis approach will be used to elucidate the role of Critical Zone structure in the climate-weathering feedback as well as account for the non-linear behavior of trace element and isotopic proxies to improve mixing models. The results of these applications will be used to inform a new global analysis of weathering processes and their implications for planetary habitability with a timescale-agnostic framework for comparing terrestrial and marine systems. To lower barriers to collecting time-series data, undergraduate engineering design teams will develop a design-for-purpose autosampler. To help engage more undergraduate students in geoscience research, the project will develop a new, outreach-based course on local water quality issues.This project is co-funded by the Hydrologic Sciences and Geobiology & Low-Temperature Geochemistry programs.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.