How does drying-driven crystalized salt influence the dynamics of water evaporation from porous media?

土壤盐渍化是指土壤中可溶性盐的过量积累，对作物、动物和人类健康产生有害影响。它是影响土壤肥力、稳定性和生物多样性的主要土地退化威胁之一，导致土壤的物理、化学和生物功能发生不良变化。除了土壤，它还对其他过程产生重大影响，如建筑材料的耐久性、路面的保存和二氧化碳的封存。盐水蒸发受多孔介质的传输特性、外部条件（如风、环境温度和相对湿度）、蒸发溶液的特性和盐结晶的影响。在土壤水分蒸发过程中，溶质通过毛细诱导的液体流动从底部湿区输送到蒸发面。同时，扩散倾向于将溶质均匀地扩散到整个区域。向上平流和扩散输运之间的竞争决定了溶质在整个土壤中的分布。当平流主导扩散时，溶质优先在靠近地表的地方沉积，导致其浓度逐渐增加。当盐浓度大大超过溶解度极限时，结晶就会在土壤表面沉淀。在表面形成的晶体形成复杂的分支结构，这可以大大增加可用蒸发的表面积。在不同的边界条件下，地表蒸发驱动的多孔结晶盐的存在究竟如何影响土壤蒸发水分的损失，目前还知之甚少。要准确预测土壤水分蒸发，需要详细了解多孔介质内流动和输运过程与地表结晶盐演化之间的复杂耦合，否则我们对这一过程的描述将取决于参数的调整。没有这些知识，人们可能会明显低估或高估陆地表面的可用水量和蒸发量，这将影响若干水文过程。在本项目中，我们计划进行全面的多尺度数值和实验研究，以量化表面蒸发驱动结晶盐的演变对多孔介质蒸发水分损失的影响。在此背景下，我们将利用最先进的数值和实验工具，如分子动力学模拟，孔隙网络和连续尺度建模，同步加速器x射线微断层扫描和定制实验室实验来实现本项目的目标。这种努力将使我们能够提供对咸水蒸发的准确描述，从而使我们能够更有力地量化土壤水蒸发和陆地-大气相互作用。

Soil salinization, referring to excess accumulation of soluble salts in soil, has detrimental impacts on crops, animal and human health. It is one of the main land-degrading threats influencing soil fertility, stability, and bio-diversity leading to undesirable changes in the physical, chemical, and biological functions of the soil. Beyond soil, it has significant impacts on other processes such as the durability of building materials, preservation of pavements, and CO2 sequestration. Saline water evaporation is influenced by transport properties of the porous media, external conditions (e.g. wind, ambient temperature, and relative humidity), properties of the evaporating solution, and salt crystallization. During water evaporation from soil, solute is transported via capillary induced liquid flow, from the wet zone at the bottom to the evaporation surface. Simultaneously, diffusion tends to spread the solute homogeneously across the entire domain. The competition between upward advection and diffusion transport determines solute distribution throughout the soil. When advection dominates diffusion, solute in preferentially deposited close to the surface leading to gradual increase of its concentration. When salt concentration substantially exceeds the solubility limit, crystals will precipitate at soil surface. The crystals formed at the surface create complex, branching structures, which can substantially increase the surface area available for evaporation. How exactly the presence of the evolving evaporation-driven porous crystallized salt at the surface influences the evaporative water losses from soil under different boundary conditions is poorly understood. Detailed information about the complex coupling between flow and transport processes within porous media and the evolving crystallized salt at the surface is required for accurate prediction of water evaporation from soil otherwise our description of this process would reply on adjusting parameters. Without such knowledge, one may notably underestimate or overestimate water availability and evaporation from land surface which will influence several hydrologic processes. In this project, we plan to conduct a comprehensive multiscale numerical and experimental investigations to quantify the effects of the evolving evaporation-driven crystallized salt at the surface on the evaporative water loses from porous media. Within this context, we will utilize the state-of-art numerical and experimental tools such as molecular dynamics simulation, pore-network and continuum-scale modelling, synchrotron X-ray micro-tomography and customized laboratory experiments to achieve the objectives of this project. Such efforts will enable us to provide an accurate description of saline water evaporation which will place us in a stronger position to quantify soil water evaporation and land-atmosphere interactions.