College of Environment Science and Engineering,Qingdao University,Qingdao
Supported by the National Natural Science Foundation of China（No. 41807010）
土壤水是地表水与地下水联系的纽带，是物质输送和运移的载体，在SPAC (土壤-植物-大气)系统中起着关键性的作用。土壤水分运动是一个非常复杂的过程，为充分了解水分在土壤中的运动过程，应用微扰动的高密度电阻率仪（ERT）监测了一层状结构的土壤剖面在注水入渗试验前、后不同时刻的电阻率的变化过程；同时，用时域反射仪（TDR）测量了点尺度上土壤体积含水量，建立了土壤电阻率和含水量的定量关系。结果表明，高密度电阻率法能够较为准确地监测土壤水分入渗深度和剖面含水量，土壤水分运动以向下的垂向运动为主并伴有微弱的水平流动；当土壤含水量低于0.15 cm3·cm-3时，随着含水量的增大，电阻率变化较大；当土壤含水量较高时，电阻率随含水量的变化不明显；根据建立的电阻率和含水量的定量关系公式，估算出在土壤界面处当上层土壤质量含水量达到0.136 g·g-1时水分开始向下层入渗，相关研究成果为定量分析土壤水在分层界面处的变化情况提供了一种新的方法。
【Objective】Soil water is the link between surface water and groundwater，and the carrier of solute transport in soil, which plays a key role in the Soil-Plant-Atmosphere Continuum (SPAC) system. The movement of soil water is a very complex process, especially in the layered structure. Heterogeneity of texture and pore of layered soil changes hydraulic characteristics at the interface of the soil layer, and thus the soil water movement and solute transport differ significantly from that in homogeneous soil．【Method】To fully understand the process of soil water movement, infiltration was evaluated using electrical resistivity tomography (ERT) in soil with a stratified profile. A field infiltration test was performed on an 8.7-m-long transect and successive measurements using ERT allowed determining resistivity changes as infiltration progressed. In the meantime, the soil water content was measured by time domain reflectometry (TDR) at the point scale, and the quantitative relationship was established between resistivity and water content. In addition, the soil water contents derived by ERT were validated with the soil water content derived by the drying method. 【Result】Results showed that the Multi-electrode resistivity method can fairly monitor the process of soil water movement, identify the depth of water infiltration, 90 cm in our study, and quantitatively retrieve the profile water content. The movement of soil water is mainly vertical downward with a weak horizontal flow. A good correlation between resistivity and soil moisture measurements revealed the capability of resistivity measurements to infer soil moisture spatial and temporal variability with root mean square error (RMSE) equal to 0.042cm3·cm-3 for loam and 0.041 cm3·cm-3 for clay loam. However, when the soil water content was lower than 0.15 cm3 cm-3, the electrical resistivity changed greatly with the increase in water content; and while the soil water content was higher, the resistivity did not change significantly with water content. When the soil water reached the interface (~30 cm) between loam and clay loam, the soil water did not immediately move to the lower layer. According to the established relationship between resistivity and water content, it is estimated that at the soil interface, when the mass moisture content reached 0.136 g·g-1 at the upper layer of the soil, the water infiltrated the lower layer. Unexpectedly, abnormally increased resistivity appeared under the area of the soil water infiltration, which was presumably caused by the significant difference in resistivity of soil adjacent layers during the infiltration process. 【Conclusion】 In comparison with TDR, the resistivity method gives information integrated on a greater volume of soil and the measurements are easier and quicker to be carried out without disturbing the soil. Therefore, this method can be considered as an alternative tool to be employed for qualitative and quantitative soil moisture monitoring in the field. Also, this study provides a new method for quantitative analysis of the movement of soil water at a layered interface.
LIN Qing, Zhang. Study of the Water Infiltration Processes using ERT and TDR in layered soils[J]. Acta Pedologica Sinica,,[In Press]