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.

土壤的拒水性对土壤质量有很大影响：它降低了持水能力，增加了地表径流、土壤侵蚀和农用化学品的优先淋溶。因此，需要更好地了解控制土壤斥水性的机制，以可持续地利用水和土壤资源。已有的研究表明，土壤疏水性与土壤有机质和土壤含水量密切相关。实验表明了一个阈值行为：在临界含水量以上，具有给定百分比土壤有机质的土壤是疏水的（接触角<90）;在该临界含水量以下，接触角迅速增加，土壤变成疏水的（CA>90）。临界含水量随土壤有机质含量的增加而降低。虽然有经验模型，能够有效地模仿这种水力行为，一个机械模型，能够预测发生不同的土壤性质的土壤防水性是失踪。本项目的目的是实施和实验验证一个孔隙尺度模型，该模型能够预测各种质地、含水量和土壤有机质含量的土壤中的防水性。我们的中心假设是，疏水表面的微观分布在宏观尺度上的润湿性的基础。我们假设，当CA>90的孔隙分数高于渗透阈值时，土壤变成防水的，渗透阈值对应于需要断开以阻止通过土壤的宏观流动的孔隙分数。我们计划开发一个三维孔隙网络模型来模拟土壤再润湿。土壤有机质（SOM）将均匀或优先分布在小孔隙中。每个孔隙的润湿性将取决于每个土壤表面的SOM的量，其空间分布和基质势。我们将测试和验证我们的模型使用的土壤混合粘液从玉米根，这是证明，使土壤防水。我们将参数化的模型测量的CA玻璃板上覆盖的粘胶。将使用环境扫描电子显微镜冷凝技术捕获孔隙空间中的粘液的原状分布。然后，我们将把我们的模型应用到自然土壤中，表现出不同程度的防水性。我们将使用X射线光电子能谱与化学界面数据的润湿性。水滴渗透的模拟将与用照相机和中子射线照相术捕获的水滴渗透时间测试进行比较，以可视化随时间的渗透和分布。毛细上升实验将进行估计动态接触角下，不同的基质电位。