A pore network model of soil water repellency: Model implementation and experimental validation

土壤拒水性的孔隙网络模型：模型实现和实验验证

• 批准号: 316989341
• 负责人: Professor Dr. Jörg Bachmann
• 金额: --
• 依托单位: Institut für Bodenkunde (IFBK)
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2016
• 资助国家: 德国
• 起止时间: 2015-12-31 至 2021-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/316989341?language=en
• 关键词: pore; network; model; soil; water

Soil water repellency has a big impact on soil quality: it reduces the water holding capacity and it enhances overland flow, soil erosion and preferential leaching of agrochemicals. Better understanding of the mechanisms controlling soil water repellency is therefore needed for the sustainable use of water and soil resources. Existing studies demonstrated that soil hydrophobicity is strongly related to two factors: soil organic matter and soil water content. The experiments indicated a threshold behaviour: above a critical water content soils with a given percentage of soil organic matter are wettable (Contact Angle<90); below this critical water content, the contact angle rapidly increases and the soil turns hydrophobic (CA>90). The critical water content decreases with increasing soil organic content. Although there are empirical models that are able to effectively mimic this hydraulic behaviour, a mechanistic model that is able to predict occurrence of soil water repellency for varying soil properties is missing. Objective of this project is to implement and experimentally validate a pore-scale model that is capable to predict the occurrence of water repellency in soils of various texture, water content and soil organic content. Our central hypothesis is that the microscopic distribution of water repellent surfaces underpins the wettability at the macroscopic scale. We hypothesize that a soil turns water repellent when the fraction of pores with CA>90 is above the percolation threshold, which corresponds to the fraction of pores that need to be disconnected to block the macroscopic flow through the soil. We plan to develop a 3D pore-network model to simulate soil rewetting. Soil organic matter (SOM) will be distributed either uniformly or preferentially in the small pores. The wettability of each pore will depend on the amount of SOM per soil surface, its spatial distribution and the matric potential. We will test and validate our model using a soil mixed with mucilage from maize roots, which was shown to make the soil water repellent. We will parameterize the model measuring the CA of glass plates covered with mucilage. The undisturbed distribution of mucilage in the pore space will be captured using the environmental scanning electron microscope condensation technique. Then we will apply our model to natural soils showing a varying degree of water repellency. We will use X-ray photoelectron spectroscopy to correlate wettability with chemical interfacial data. Simulation of water drop infiltration will be compared to water drop penetration time tests captured with a camera and neutron radiography to visualize the infiltration and distribution over time. Capillary rise experiments will be performed to estimate the dynamic contact angle under varying matric potentials.

土壤水对土壤质量的影响很大：它降低了水的容量，并增强了陆上流动，土壤侵蚀和农业化学的优先浸出。因此，对于可持续使用水和土壤资源，需要更好地了解控制土壤水的机制。现有的研究表明，土壤疏水性与两个因素密切相关：土壤有机物和土壤水含量。实验表明阈值行为：在给定的土壤有机物百分比的关键水分含量土壤上方是可润湿的（接触角<90）；在此临界水含量的下方，接触角迅速增加，土壤变成疏水（Ca> 90）。临界水含量随着土壤有机含量的增加而降低。尽管有一些经验模型能够有效地模仿这种液压行为，但缺少能够预测土壤水排斥的机械模型，而土壤水则存在变化的土壤特性。该项目的目的是实施和实验验证孔隙尺度模型，该模型能够预测各种质地，水含量和土壤有机含量的土壤中水的发生。我们的中心假设是，驱虫表面的显微镜分布是宏观尺度上的润湿性的基础。我们假设，当Ca> 90的毛孔的比例高于渗透阈值时，土壤会变成驱虫剂，这对应于需要断开孔隙以阻断宏观流经土壤的孔的比例。我们计划开发一个3D孔网模型，以模拟土壤重新吹干。土壤有机物（SOM）将均匀或优先分布在小毛孔中。每个孔的润湿性将取决于每个土壤表面的SOM量，其空间分布和矩阵电位。我们将使用与玉米根中的粘液混合的土壤进行测试和验证我们的模型，这被证明会使土壤驱虫剂。我们将参数化测量玻璃板的CA的模型。孔隙空间中粘液的不受干扰的分布将使用环境扫描电子显微镜冷凝技术捕获。然后，我们将把模型应用于自然土壤，表现出不同程度的排水。我们将使用X射线光电子光谱法将润湿性与化学界面数据相关联。将水滴浸润的模拟与用摄像头和中子射线照相捕获的水滴渗透时间测试进行比较，以可视化随着时间的推移渗透和分布。将进行毛细管上升实验，以估计不同矩阵电位下的动态接触角。