Application Of ERT Technology In The Study Of Water Movement In The Aerated Zone Of Red Soil

The water in soil is the material basis for the survival of all living things,and plays an important role in the four-water transformation.The movement of soil water is the main driving force for the transfer of matter and energy in soil.However,the movement of water in soil is complicated and changeable,which is difficult to capture directly,especially in red soil areas with abundant rainfall and diverse land use types.Therefore,with the help of physical detection technology,high density electrometer(ERT),combined with point scale monitoring of soil water and groundwater level,this study explores underground hydrological information of key zones of red soil,establishes the functional relationship between the resistivity measured by ERT and soil water content,defines the occurrence process of priority flow in red soil region,and compares the differences among land use types.The results showed that :(1)the soil conductivity of agricultural slope in the red soil area has a good hierarchy,and the soil water status is an important determinant of this hierarchy.Based on the difference of electrical resistivity,the underground part of the farmland slope of red soil can be divided into four layers: layer 1,the depth is 0～1.0m,the resistivity value is greater than 600 ohm·m,the soil water content is relatively low,small bulk density;In the second layer,the depth is 1.0～2.5 m,and the resistivity value is between 300 and 600ohm·m.The soil water content and bulk density of this layer are in the middle.In the third layer,the depth is 2.5～5.5m,and the resistivity value is between 100～300ohm·m.The soil moisture content of this layer is close to saturation,and the bulk density is large: in the fourth layer,the depth is below 5.5m,the resistivity value is between 0 and 100 ohm·m,and this layer is the soil saturation zone.(2)ERT can be used to quickly detect the location of soil saturation zone.The resistivity is very sensitive to the boundary between the saturated zone and the unsaturated zone.The boundary of the saturated zone detected by ERT is in good agreement with the measured groundwater level.(3)Electrode spacing affects the accuracy of soil water retrieval by ERT.The apparent resistivity of agricultural land was negatively correlated with soil water content,but the degree of correlation was significantly affected by the electrode spacing.When the electrode spacing was 75 cm,the correlation between the two was the strongest,and the coefficient of determination was 0.72(P<0.01).With the increase or decrease of the electrode spacing,the accuracy of ERT retrieval of soil water decreased.When the electrode spacing decreased to 150 cm,the coefficient of determination decreased to 0.65(P<0.01),and when the electrode spacing increased to 50 cm,the coefficient of determination decreased 0.52(P<0.01),when the electrode spacing was further reduced to 25 cm,there was no correlation between the two,the coefficient of determination was only0.04(P>0.05).By increasing the variation range of soil water and improving the hierarchical correspondence between resistivity and soil water data through artificial water injection,the correlation between the two can be significantly improved,even under the condition of high density electrode placement(electrode spacing is 30 cm).A significant functional relationship between resistivity and soil moisture could also be established,with a coefficient of determination of 0.53(P<0.01).(4)The performance of ERT technology in red soil region was affected by land use type.In Hong Tong District,the land use pattern is affected by land use pattern.The apparent resistivity of forest land is significantly higher than that of agricultural land,and the former is ten times that of the latter.Under the condition that the terrain,parent material and water are basically the same,the difference of resistivity between the two is probably related to the number of large pores in the soil,and there are a lot of plant roots and animal holes in the forest land.In addition,the functional relationship between resistivity and soil moisture was also related to land use type,with exponential negative correlation for farmland and power function relationship for forest land.(5)Land use mode affects the occurrence mode of preferential flow in red soil region.ERT technology can visualize the occurrence process of preferential flow.In terms of intensity,the preferred flow of forest land is more developed.In terms of form,the preferred flow of forest land mainly moves along the macropores such as plant root holes or animal burrows,while in agricultural land,the preferred flow is mainly in the form of vertical "finger flow",in which water accumulates to a certain degree at a level with poor water conductivity and then moves down rapidly.The research results of this paper can deepen the understanding and understanding of the law of water movement in red soil region,especially the occurrence process of priority flow,and provide strong scientific support for the solution of ecological environment problems in regions with similar hydrological and climatic conditions.