A Cross Site Study of Silica Dynamics in the Critical Zone

该项目旨在研究NSF临界区观测网络（CZO）内一系列溪流集水区的二氧化硅生成和运输动态。 溶质浓度和化学成分随河流流量以复杂的方式变化。 在某些情况下，溶质负荷仅随流量略有变化。 在其他系统中，溶质浓度随着排放量的增加而下降，显示出稀释效应，但即使在这些系统中，稀释也只是部分的。 如果流量增加而溶质浓度保持接近恒定，则总溶质负荷也增加。 水文地球化学中的一个重要问题是溶质通量的增加来自何处？ 流只是简单地采样“更多的相同”，还是在高流量时激活了新的来源和途径？换句话说，水质是如何随着排放而变化的，为什么？二氧化硅（Si）非常适合解决这个问题，因为它主要来源于岩石和土壤的风化反应，并且作为水文示踪剂有着悠久的历史。 研究人员以前已经表明，锗/硅比可以用来确定特定来源的硅在一个集水区，并大大提高了效用的硅作为示踪剂。初步数据表明，与高放电相关的硅通量增加会激活新的硅源。 本研究将使用一系列集水区在CZO网站，具有相似的岩石类型，但不同的气候，植被和水化学响应模式，以了解更多关于溶质来源和水质的基本控制。 建议的研究将提供新的地球化学和水文过程，控制硅通量的花岗岩风化的关键区的限制。 它将解决溪流中不同浓度-排放模式的原因，深入了解风化和水文过程的耦合，并为过程线分离/流动路径建模提供改进的基础。 该项目将使用新的地球化学示踪剂和临界区观测站网络，以了解对土壤和地下水流动路径以及河流流域水质的一些主要控制。 二氧化硅不仅是水文路径和溶质来源的有用示踪剂，而且是河流化学的重要缓冲剂，是水生和陆生藻类和植物的重要营养物质，并且与二氧化碳的长期风化汇有关。 对水流路径和溶质负荷的短期控制以及风化通量的长期控制的进一步理解具有广泛的意义。该项目包括与来自几个CZO的学生和研究人员合作，并将培训来自其他CZO团队的学生测量和使用Ge/Si作为水文地球化学示踪剂。预计这将有助于增加关键区科学界对Ge/Si和其他水文地球化学示踪剂的理解和使用。

This project proposes to investigate the dynamics of silica generation and transport across a series of stream catchments within the NSF Critical Zone Observatory Network (CZO). Solute concentrations and chemical compositions vary with stream discharge in complex ways. In some cases, solute load varies only slightly with stream discharge. In others, solute concentrations drop as discharge increases, showing effects of dilution, but even in these systems dilution is only partial. If stream discharge increases while solute concentration remains near constant, then the total solute load most also increase. An important question in hydrogeochemistry is where does this increase in solute flux come from? Do streams simply sample "more of the same", or are new sources and pathways activated at high flow? In other words, how does water quality vary with discharge, and why? Silica (Si) is well suited for addressing this question as it is primarily sourced from rock and soil weathering reactions, and has a long history of use as a hydrologic tracer. Investigator has previously shown that germanium/silicon ratios can be used to identify specific sources of Si in a catchment, and substantially improve the utility of Si as a tracer. Preliminary data indicate that increased in Si flux associated with high discharge activate new sources of Si. This study will use a series of catchments at CZO sites that have similar rock type but different climate, vegetation, and hydrochemical response patterns in order to learn more about the fundamental controls on solute sources and water quality. The proposed research will provide new constraints on the geochemical and hydrological processes that control Si fluxes from granitoid weathering in the critical zone. It will address the causes of different concentration-discharge patterns in streams, providing insight into the coupling of weathering and hydrologic processes, and providing an improved basis for hydrograph separation/flow path modeling. The project will use novel geochemical tracers and the network of Critical Zone Observatories to understand some of the major controls on soil and ground water flow paths and water quality in stream catchments. Silica is not only a useful tracer of hydrologic pathways and solute sources, but also an important buffer of stream chemistry, an important nutrient for both aquatic and terrestrial algae and plants, and is tied to the long term weathering sink of carbon dioxide. An improved understanding of both the short term controls on water flow paths and solute loads, and the longer term controls on weathering fluxes is of broad interest. The project includes working with students and researchers from several CZOs, and will train students from other CZO teams in the measurement and use of Ge/Si as a hydrogeochemical tracer. It is expected that this will help increase the understanding and use of Ge/Si and other hydrogeochemical tracers among the Critical Zone science community.