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，当雨水或其他方式把水加到土壤表面时，土壤表面的水珠就会脱落。然后，随着时间的推移，土壤发生变化，能够吸收水分。这一过程称为动态分数润湿性或土壤拒水性。动态分数润湿性极大地改变了土壤中水分的行为及其在植物生长、养分循环和污染物运输中的可用性。在许多重要的环境条件下，土壤润湿性的变化过程是非常复杂和不可预测的。例如，在森林野火之后，土壤通常变得高度排斥，导致雨水过量流失，从而造成侵蚀。此外，在驱避土壤中保留的水量也大大减少，这直接影响植物生长、种子发芽、土壤蒸散和土壤温度。由于这种排斥作用，在地表形成池塘的水可以顺着土壤中的裂缝和大孔隙（如旧的根通道）流失，绕过浅层土壤和大多数植物的根，从而更快地进入地下水。类似的动态分数润湿性问题也发生在石油泄漏后或旧工业场地的土壤中（棕地）。不幸的是，我们目前的科学知识和预测水如何移动、储存或释放的能力是严重缺乏的，土壤随着时间的推移有不同程度的排斥水的倾向（动态分数润湿性）。我们目前的科学知识是这样的，目前没有机械的计算机模型可以准确地描述这些复杂动态土壤中的水行为和/或在这些条件下污染物的补充和输送到地下水。过去几十年的研究表明，土壤水分分数润湿性/驱避性比以前已知/认识到的要普遍得多，并且在许多重要的环境条件下可能是水运动的主要驱动因素。这项NSERC发现资助研究计划的目标是提高我们对基本概念的理解和数学模型的能力，并预测土壤中的水流和污染物运输，表达动态的分数润湿性/拒水性。这将通过实地实验、高度仪器化的实验室测试/实验、代表性土壤材料的孔隙尺度成像和模型开发来完成。结果将是新的/更好的土壤水流模型，土壤水分储存，以及土壤和地下水中相关的污染物运输，可以用来帮助解决许多相关的紧迫的环境问题，这些问题受到动态分数润湿性的主要影响。

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.