Knowledge Resource Center for Ecological Environment in Arid Area
| 项目编号 | 0510825 |
| Cyclic Processes Within Surface-exposed Fractures Affecting Evaporation and Salinization Mechanisms | |
| Maria Dragila | |
| 主持机构 | Oregon State University |
| 开始日期 | 2005-08-01 |
| 结束日期 | 2010-07-31 |
| 资助经费 | 349740(USD) |
| 项目类别 | Continuing Grant |
| 资助机构 | US-NSF（美国国家科学基金会） |
| 项目所属计划 | Hydrologic Sciences |
| 语种 | 英语 |
| 国家 | 美国 |
| 英文简介 | 0510825 Dragila This 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 have been 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 fracturedchalk site. 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 the PI'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 readily tangible 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. |
| 来源学科分类 | Geosciences |
| URL | https://www.nsf.gov/awardsearch/showAward?AWD_ID=0510825 |
| 资源类型 | 项目 |
| 条目标识符 | http://119.78.100.177/qdio/handle/2XILL650/342366 |
| 推荐引用方式 GB/T 7714 | Maria Dragila.Cyclic Processes Within Surface-exposed Fractures Affecting Evaporation and Salinization Mechanisms.2005. |
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