The Role of Fractional Dynamic Wettability as a Primary Determinant for Flow and Transport in Soils and the Vadose Zone.

在一些土壤中，当水通过雨水或其他方式作用于地表时，水会在地表形成水珠，然后流失。然后，随着时间的推移，土壤发生变化，变得能够吸收水分。这一过程被称为动态分数润湿性或土壤排水性。动态分数润湿性极大地改变了土壤中水分的行为及其对植物生长、养分循环的有效性，以及它在污染物传输中的作用。在许多重要的环境条件下，改变土壤润湿性的过程是非常复杂和不可预测的。例如，在森林野火之后，土壤通常会变得高度排斥，从而导致过度的降雨径流，从而导致侵蚀。此外，土壤中滞留的水分大大减少，这直接影响植物的生长、种子萌发、土壤蒸散和土壤温度。由于排斥性，在地表形成池塘的水可以排出土壤中的裂缝和大孔隙(如旧的根沟)，绕过浅层土壤和大多数植物根，随后更快地到达地下水。在石油泄漏后的土壤或老工业场地(棕地)，也存在着对地表以下动态润湿性的类似担忧。不幸的是，我们目前的科学知识和能力严重缺乏预测水如何移动以及从土壤中储存或释放的能力，这些土壤随着时间的推移有不同程度地排斥水(动态分数润湿性)。我们目前的科学知识状况是，目前还没有机械的计算机模型可以准确地描述这些复杂的动态土壤中的水行为和/或在这些条件下污染物向地下水的补给和运输。过去几十年的研究表明，土壤水分的润湿性/排斥性比以前所知/认识的要普遍得多，在许多重要的环境条件下，它可能是水分运动的主要驱动力。NSERC Discovery Grant研究项目的目标是促进我们对基本概念的理解和对土壤中的水流和污染物传输进行数学建模和预测的能力，以表达动态分数润湿性/排水性。这将通过现场实验、高度仪器化的实验室测试/实验、典型土壤材料的孔隙尺度成像和模型开发来完成。其结果将是新的/更好的土壤水流动、土壤水储存以及土壤和地下水中相关污染物运移的模型，可用于帮助解决受动态分数润湿性主要影响的许多相关和紧迫的环境问题。

In some soils when water is applied to the surface by rain or other means the water beads on the surface and runs off. Then, over time the soil changes to become able to soak up the water. This process is called dynamic fractional wettability or soil water repellency. Dynamic fractional wettability drastically changes the behaviour of water and its availability in soils for plant growth, nutrient cycling, and it role in contaminant transport. The process of changing wettability of soils is very complex and unpredictable under many important environmental conditions. For example, after a forest wildfire the soil is commonly rendered highly repellent leading to excessive runoff of rain with resultant erosion. Also, the amount of water that is retained in repellent soil is greatly reduced which directly affects plant growth, seed germination, soil evapotranspiration, and soil temperature. Water that does pond on the surface due to the repellency can drain down fractures and large pores in the soil (like old root channels) and bypass the shallow soil and most plant roots to subsequently arrive in groundwater much more quickly. Similar concerns of dynamic fractional wettability below ground surface occur in soils after petroleum spills or at old industrial sites (Brown Fields). Unfortunately, our current scientific knowledge and ability to predict how water moves and is stored or released from soils that have the tendency to repel water to varying degrees over time (dynamic fractional wettability) is critically lacking. The current state of our scientific knowledge is such that there are currently no mechanistic computer models that can accurately describe water behaviour in these complex dynamic soils and/or resultant recharge and transport of contaminants to ground waters under these conditions. Research over the last few decades has revealed that soil water fractional wettability/repellency is far more common than previously known/recognised and is potentially a primary driver for water movement under a number of important environmental conditions. The objectives of this NSERC Discovery Grant research program are to advance our fundamental conceptual understanding and ability to mathematically model and predict water flow and contaminant transport in soils expressing dynamic fractional wettability/water repellency. This will be done through field experiments, highly instrumented laboratory testing/experiments, pore-scale imaging in representative soil materials, and model development. The outcome will be new/better models of soil water flow, soil water storage, and related contaminant transport in soil and groundwater that can be used to help solve many related and pressing environmental problems subject to the primary effects of dynamic fractional wettability.