Isotope Fractionation of Water Adsorption on Clay Minerals

陆地环境土壤-水系统处于陆地-大气-植被能量-水-二氧化碳平衡和生态系统的一个非常关键的界面。该项目的结果有助于我们更好地了解地块、区域和全球尺度上的陆地-大气-植被系统。推而广之，这种认识的提高可以更准确地预测区域到全球的水循环和可能的气候变化。这种能力越来越需要满足社会需求，如水资源开发，全球初级生产，农业/粮食生产和安全。研究者将开展一项外展活动，旨在通过为期一天的关于水相关项目的互动“水星球”研讨会，提高来自西德克萨斯州农村的中学女生对STEM主题的兴趣。土壤水的同位素组成作为一种非常有效的工具被广泛应用于研究水汽带水文，包括蒸散发、水运动和地下水补给。近年来，基于同位素的研究发现，流域流动水（以溪流水为代表）和紧密结合水（以土壤和植物水为代表）在同位素上是不同的。特性分离?已经提出。对观测到的同位素差异的其他解释包括在渗透过程中蒸发和未蒸发的土壤水的混合。该项目提出的活动和预期结果将检验这样一种假设，即与土壤矿物表面和孔隙中水的吸附和冷凝有关的同位素分馏与散装液态水的分馏不同。本研究寻求一种详细、系统的实验和基本建模的综合方法，以量化、理解和预测各种非膨胀粘土（高岭土）、膨胀粘土（富钠和富钙蒙脱土）和土壤中吸附水的同位素分异，并将其作为物理化学性质（表面化学、孔径/层间距离、层间阳离子类型）和相对蒸汽压的函数。由于土壤水的同位素组成已得到越来越广泛的应用，该结果的潜力对我们对陆地-大气-植被界面水循环的理解具有深远的意义。可以直接影响和进一步发展的知识包括：a)土壤水同位素组成的分析方法，b)土壤孔隙和裂缝中具有不同同位素组成的多个地下水池，以及c)分别计算土壤和植被蒸发和蒸腾通量同位素组成的Craig-Gordon蒸发模型。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 soil-water system of terrestrial environments is located at a very critical interface within land-atmosphere-vegetation continuum of the energy-water-carbon dioxide balance and ecological systems. The outcome from this project can contribute to our better understanding of the land-atmosphere-vegetation system on plot to regional to global scales. By extension, the improved understanding can lead to more accurate prediction of regional to global water cycles and likely climate changes. Such capability is increasingly required to meet societal needs such as water resources development, global primary production, and agriculture/food production and security. The investigator will conduct an outreach activity designed to enhance middle school girls' interest from rural West Texas in STEM topics through a one-day, interactive "Water Planet" workshop on water-related projects.The isotopic compositions of soil waters have been extensively utilized as a very effective tool to study vadose-zone hydrology, including evapotranspiration, water movement, and groundwater recharge. Recently, isotope-based studies found that mobile water (expressed by stream water) and tightly bound water (represented by soil and plant water) in watersheds were isotopically distinct and the notion of ?ecohydrological separation? has been proposed. Other explanations of the observed isotopic differences include a mixing of evaporated and unevaporated soil waters during percolation. The proposed activities and expected outcome from this project will test the hypothesis that isotope fractionation associated with the adsorption and condensation of water on the surface and in pores of soil minerals differ from that for bulk liquid water. This proposal seeks an integrated approach of detailed, systematic experiments and basic modeling to quantify, understand and predict the isotope fractionation of adsorbed water on various non-expansive clay (kaolinite), expansive clays (Na- and Ca-rich montmorillonite), and soils in general as a function of physicochemical properties (surface chemistry, pore size/interlayer distance, type of interlayer cations) and the relative vapor pressure. The potential of the outcome has far-reaching implications for our understanding of the water cycle at the land-atmosphere-vegetation interface, because the isotopic compositions of soil water has been increasingly and widely used. Knowledge that can be directly impacted and further advanced include: a) analytical methods for the isotopic compositions of soil water, b) multiple subsurface water pools in soil pores and fractures with different isotopic compositions, and c) Craig-Gordon evaporation model for calculating the isotopic compositions of evaporation and transpiration fluxes from soils and vegetation, respectively.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.