Cyclic Processes Within Surface-exposed Fractures Affecting Evaporation and Salinization Mechanisms

这个项目将研究近地表裂缝中的化学物理过程，这可能是导致盆地规模蒸发增强和溶质(盐度)加速向地下水输送的原因。在干旱和半干旱地区，地下水是一种稀缺商品，地下水盐碱化已成为一个日益严重的问题。同样的机制也令人感兴趣，因为废物设施通常位于这些类型的环境中。盐壳的形成是各种重要机制相互作用的结果，如渗透率、渗透势和热能的梯度。这些过程可以协同作用减少或加强盐壳的形成，包括：(1)夜间排气时加速蒸发；(2)导致水蒸气泵送和盐反扩散的渗透梯度；(3)可能堵塞内部孔隙和/或造成岩石表面封闭的盐沉淀；(4)可能影响裂缝孔径的盐壳形态；以及(5)可能改变表面结构和蒸发速率的盐蚀。尽管已经在现场或在前期工作中观察到了这些机制，但长期效果还没有得到评估。工作模型包括一个带有裸露表面裂缝的包气带。当这些裂缝充满空气时，裂缝壁的蒸发会触发毛细管力，从基质中吸取孔隙水和溶质，发生进一步的蒸发，从而导致盐分在裂缝壁上积累增强。白天的蒸汽压梯度驱动了一个相对缓慢的扩散过程，将潮湿的裂缝空气排出。然而，在夜间，不稳定的空气密度梯度允许密度较高的地面空气进入裂缝，导致潮湿裂缝空气的大量对流和喷发，从而增加裂缝表面的蒸发，并促进伴随的盐壳形成。理论分析表明，夜间对流通风可能会使蒸发势增加80倍。近地表破裂作为反应性对流单元的概念和夜间对流的概念直到最近才被研究。本项目将重点研究在各种自然条件下这种对流喷发对盐壳形成的影响。这项拟议的研究将使用气候控制室(OSU)和X射线CT扫描(PSU)来研究岩石岩心内不同渗透率范围内蒸发和盐分沉积的孔隙尺度过程。中尺度实验将在大型气候控制室(BGU)中进行，以探索天然裂隙岩石在受控条件下的上述机理。将在实际裂缝(仪器深度为~1.4m)中研究现场尺度的排气和蒸发动力学。位于一个特征良好的碎屑岩中。数值模型将被用来量化这一过程对污染物绕过、溶质向含水层的加载和盆地尺度蒸发的影响。最重要的是，该项目将确定这一过程的极限参数，即在什么地质和气候条件下，这一过程将是最重要的。智力上的优点：除了作为流体的快速管道外，开放(充气)空腔在包气带水动力中的作用在很大程度上被忽视了。有大量的现场证据表明，在漫长的旱季期间，穿越上包气带的裂缝表面确实沉淀了盐化结壳，强调了研究这一过程的必要性。除了国际海洋研究所最近提交发表的报告外，我们不知道关于这一主题的任何处理方法。该项目的设计不仅将促进对盐结壳过程的基本了解，而且还将建立对盆地规模水文学重要的参数。旱地水文学的适用性了解从废物设施转移污染物渗漏的可能性。广泛的影响：该项目是俄勒冈州立大学、宾夕法尼亚州立大学和以色列内盖夫的本古里安大学之间国际合作的结果。参与该项目的两名学生将在国际跨学科环境中工作，培养他们作为未来科学家取得成功所必需的合作技能。由于科学教育是国家的优先事项，该项目还将参与NSF G-K12计划，其双重目标是向教育工作者传播研究成果，并为随时准备好的研究生提供教学培训，这些培训是有形的和鼓舞人心的，有助于进一步研究。该项目将为在职K-12教师开发一个讲习班单元，在一所参与的小学试行一个专题单元，开发一个可借给感兴趣的教育工作者的“教材包”，并为那些希望复制该教材包和单元的人建立一个网站。

0510825DragilaThis project will investigate chemico-physical processes in near-surface fractures that may be responsible for enhanced basin-scale evaporation and accelerated transport of solutes (salinity) to groundwater. In arid and semiarid regions where groundwater is a scarce commodity, groundwater salinization has become an ever-increasing concern. This same mechanism is also of interest because of the waste facilities typically located in these type environments. Salt crust formation is the result of a complex process caused by the interaction of various important mechanisms, such as gradients in permeability, osmotic potential and thermal energy. These processes can act in concert to either reduce or enhance salt crust formation, including: (1) accelerated evaporation during nighttime venting; (2) osmotic gradients that result in vapor pumping and saline back-diffusion; (3) salt precipitation that can clog internal pores and/or cause surface sealing of the rock; (4) salt crust morphology that can impact fracture aperture; and (5) haloclasic erosion that can change the surface texture and evaporation rate. Even though these mechanisms havebeen observed either in the field or during preliminary work, the long-term effect has not been evaluated.The working model consists of a vadose zone with exposed surface fractures. When these fractures are air filled, evaporation from the fracture walls triggers capillary forces that draw pore-water and solutes from the matrix where further evaporation occurs, thus resulting in enhanced salt accumulation on the fracture walls. Daytime vapor pressure gradients drive a relatively slow diffusional process that vents moist fracture air. During nighttime, however, unstable air-density gradients permit denser surface air to enter the fracture resulting in mass convection and venting of moist fracture air, thus enhancing evaporation of the fracture surface and enhancing concomitant salt crust formation. Theoretical analysis indicates that nighttime convective venting may increase evaporative potential by a factor of 80. The concept of a near-surface fracture serving as a reactive convection cell and the concept of nighttime convection has only recently been investigated. This project will focus on the impact that this convective venting has on salt crust formation under various natural conditions. The proposed research will use a Climate Control Chamber (OSU) and x-ray CT-scanning (PSU) to investigate pore-scale processes of evaporation and salt deposition within rock cores for a range of permeabilities. Intermediatescale experiments will be conducted in a large Climate Controlled Room (BGU) to explore the aforementioned mechanisms under controlled conditions for a natural fractured rock. Field-scale venting and evaporation dynamic will be investigated in a real fracture (instrumented to a depth of ~1.4 m.) located at a well-characterized fracturedchalksite. Numerical models will be used to quantify basin scale impact of this process on contaminant bypassing, solute loading to aquifer and basin scale evaporation. Most importantly the project will determine the limiting parameters for this process, i.e., under which geologic and climatic conditions will this process be most important.Intellectual Merit:The role of open (air-filled) cavities in vadose zone hydrodynamics has been largely ignored, except as rapid conduits of fluids. There is substantial field evidence that salty crust is indeed precipitated on the surfaces of fractures that cross the upper vadose zone during the long dry season emphasizing the need to investigate this process. We are not aware of any treatments of this topic outside of those recently submitted for publication by thePI's. The project design is such that it will not only develop fundamental understanding of the salt crusting process, but also establish the parameters important for basin scale hydrology. Applicability within arid land hydrology understanding the potential for diverted contamination seepage from waste facilities.Broader impacts:This project is the result of international collaboration between Oregon State University, Pennsylvania State University and Ben Gurion University of the Negev, Israel. Two students involved in the project will work in an international interdisciplinary setting developing collaborative skills essential for their success as future scientists. Because science education is a national priority, the project will also participate in the NSF G-K12 Program with the dual goal of disseminating research results to educators and providing pedagogical training to graduate students readilytangible and inspiring toward the pursuit of further research. The project will develop a workshop unit for in-service K-12 teachers, pilot a thematic unit at a participating primary school, develop a "teaching kit" that can be on loan to interested educators, and a web site for those who wish to replicate the teaching kit and unit.