Groundwater Salinization in a Fractured Arid Environment
Investigators (most current known information)
Groundwater salinization is a problem in many arid environments throughout the world. We are investigating a mechanism of salinization that involves the formation of salt crust on surface-exposed fractures during dry seasons and dissolution of this crust during precipitation events. Pore water can move laterally through matrix to an exposed fracture if the relative humidity in the fracture is less than 100%. Evaporation from the fracture surface can elevate solute concentrations in the adjacent pore water, which upon reaching saturation will precipitate as an efflorescent crust on the fracture surface. During the wet season, this salt can be dissolved in infiltrating water during precipitation events. If the infiltrating water reaches the water table, a measurable increase in solute concentration may result. The project goal was to test a conceptual model that convective venting of moist air within fractures is the dominant mechanism governing evaporation and can result in salt crust accumulations significantly in excess of those predicted from purely diffusive venting of fractures.
Significant advancement in our understanding of this phenomenon and our ability to quantify if its effect on the landscape has been achieved over the project period. This final report covers the progress in scientific understanding and the project outcomes.
The laboratory work was successful in reproducing field thermal gradients within the soil matrix, and convectively driven enhanced evaporation rates from the fracture aperture. Laboratory work permitted quantification of salt crust formation and was used for calibrating the numerical models. It was shown that evaporation from surface-exposed fractures significantly increases during night-time desert conditions relative to day-time conditions. Most importantly, the grant permitted the construction of a sophisticated laboratory and field infrastructure where investigations on this process continue. Numerical models expanded the set of laboratory parameters investigated and initiated an investigation on the potential impact of this process under field conditions. We are convinced that the outcome of this work notably contributes to understanding the mechanism of groundwater salinization in dry environment and will lead to better prediction of the groundwater salinization process as well as the role played by fractures in controlling fluid and solutes movement in shallow subsurface of the earth.
In addition to fostering a very successful collaboration between the three principal investigators on the project, two students have graduated with Master of Science degrees and have continued their graduate education by entering into Ph.D. program in the area of water resources. Both students developed thesis from this project. One graduate student at Ben-Gurion University of the Negev focused on experimental work. The second graduate student at Oregon State University concentrated on the numerical model. The project led to the publication of one book chapter ( American Geophysical Union (AGU) Monograph) and one paper in peer reviewed scientific journal (J. Arid Environments). Additional manuscript is currently under review ( Soil Science Society of American Journal ) and another one is in preparation. The results of this work have also presented in several national and international conferences (AGU conference on fracture flow; AGU annual meeting; Geological Society of Israel meetings) and will be presented in more conferences soon (e.g., Gordon conference).
No outcomes reported