Study of the Water Infiltration Processes using ERT and TDR in Layered Soils
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S152.7

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Supported by the National Natural Science Foundation of China(No. 41807010)

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    Abstract:

    【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 0.042 cm3·cm-3 for loam and 0.041 cm3·cm-3for 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, 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.

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LIN Qing, XU Shaohui. Study of the Water Infiltration Processes using ERT and TDR in Layered Soils[J]. Acta Pedologica Sinica,2023,60(2):390-398.

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History
  • Received:April 28,2021
  • Revised:November 17,2021
  • Adopted:January 12,2022
  • Online: January 12,2022
  • Published: March 28,2023