Isotope Fractionation of Water Adsorption on Clay Minerals

粘土矿物水吸附的同位素分馏

• 批准号: 1804838
• 负责人: Juske Horita
• 金额: $ 35万
• 依托单位: Texas Tech University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2018
• 资助国家: 美国
• 起止时间: 2018-09-01 至 2022-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1804838&HistoricalAwards=false
• 关键词: Isotope; Fractionation; Water; Adsorption; Clay

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.

陆地环境的土壤-水系统处于能量-水-二氧化碳平衡和生态系统的陆地-大气-植被连续体中一个非常关键的界面。该项目的研究结果有助于我们从区域到全球尺度更好地了解陆-气-植被系统。通过扩展，改进的理解可以导致更准确地预测区域到全球的水循环和可能的气候变化。为了满足水资源开发、全球初级生产以及农业/粮食生产和安全等社会需求，越来越需要这种能力。研究者将通过为期一天的关于水相关项目的互动式“水星球”研讨会开展旨在提高西德克萨斯州农村中学女生对STEM主题的兴趣的推广活动。土壤沃茨的同位素组成已被广泛用作研究包气带水文学的非常有效的工具，包括蒸散，水运动和地下水补给。最近，基于同位素的研究发现，流域中的移动的水（以溪流水表示）和紧密结合的水（以土壤和植物水表示）在同位素上是不同的。生态水文分离已经被提议了。对所观察到的同位素差异的其他解释包括在渗滤过程中蒸发和未蒸发的土壤沃茨的混合。该项目的拟议活动和预期成果将检验以下假设：与水在土壤矿物表面和孔隙中的吸附和凝结有关的同位素分馏不同于大量液态水的同位素分馏。该提案寻求一种详细、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性粘土（高岭石）、膨胀性粘土（富含Na和Ca的蒙脱石）和土壤上吸附水的同位素分馏，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理解陆地-大气-植被界面的水循环具有深远的意义。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）用于计算土壤和植被蒸发和蒸腾通量的同位素组成的Craig-Gordon蒸发模型，该奖项反映了NSF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。