基于ERT的黄土高原小流域典型坡地和坝地土壤储水量反演

Variation of Soil Water over Slopes and Retained Lands in Loess Region:Investigated Using Electrical Resistivity Tomography

【目的】反演黄土高原小流域典型坡地和坝地的土壤储水量(SWS),为小流域水资源管理与生态建设提供科学依据。【方法】在陕北六道沟小流域选择典型坡地和坝地,利用电阻率层析成像法(ERT)测定其土壤电阻率(ρ),结合实测土壤体积含水率(θv),构建ρ与θv的幂函数模型,量化0~12.5 m土层剖面的SWS,并对比分析坡地与坝地的SWS空间分布差异。【结果】对于黄土高原坡地和坝地2种典型地貌类型,ρ与θv之间均具有显著的幂函数关系(坡地:R^(2)=0.66,p<0.01;坝地:R^(2)=0.64,p<0.01);坡地ρ分布受坡位影响显著,沿坡顶至坡底逐渐降低,坝地ρ在垂直方向上呈“高-低-高”的分布格局,具有明显的饱和层和非饱和层,而坡地剖面均为非饱和状态;面积为1.8×10^(4)m^(2)的坝地0~6.5 m非饱和层的可储水量为1.49×10^(4)m^(3),6.5~12.5 m饱和层可储水量为5.10×10^(4)m^(3);而相近面积的坡地0~12.5 m非饱和层可储水量为2.59×10^(4)m^(3)。【结论】ERT可用于黄土区深层土壤水资源时空分布研究,六道沟小流域坝地土壤储水量丰富,是坡地土壤储水量的2.5倍,对小流域的水循环和生态系统服务具有重要作用。

【Objective】Crop growth and ecological functions in arid and semi-arid loess regions in northwestern China are limited not only by topsoil water directly available to crop but by deep soil water which functions as a reservoir.Slopes and lands formed by artificial retaining are two typical geographical units in small watersheds in the loess plateau.This paper presents a method to estimate soil water distribution in them up to 12.5 m deep.【Method】The method was based on electrical resistivity tomography(ERT).We measured electrical resistivity of the soil in typical slope and retained land in the small Liudaogou watershed in northern Shaanxi province.Using the measured soil volumetric water content,a power function relating the resistivity to soil water content was established,from which we calculated water distribution and water storage in the 0~12.5 m profile in both the slope and the retained land.【Result】The distribution of electrical resistivity over the slope was significantly affected by slope position,with the resistivity decreasing gradually from the slope top to the slope toe.Such changes were associated with vegetation consumption of the topsoil water and redistribution of the infiltrated precipitation over the slope.The vertical distribution of the resistivity in the retained land showed a high-low-high variation;this was also related to root water uptake from the topsoil and precipitation recharge to the subsoil.ERT inversion showed co-existence of a saturated zone and an unsaturated zone in the retained land,while the slope was partly saturated.In a 1.8×10^(4)m^(2)of retained land,there was 1.49×10^(4)m^(3)of water in the 0~6.5 m unsaturated layer,and 5.10×10^(4)m^(3)of water in the saturated layer.In a same area but on the slope,there was only 2.59×10^(4)m^(3)of water in the 0~12.5 m soil layer.【Conclusion】Retained land contains more water than slope,and the deep soil in it functions as a reservoir banking infiltration water in wet seasons.ERT is suitable for measuring spatiotemporal variation in soil moisture in both slopes and flatten plains in the loess plateau.