Role of clay in water flow and solute transport in soils

在实验室土柱中对土壤中的水流和溶质运移进行了密集的监测，以研究粘土在土壤中流动和运移中的作用。本研究取得了以下三个主要成果。(1)对于原状和扰动的日本火山灰土、安迪土和低膨胀度的有明土，高膨胀性膨润土对Na-Ca混合溶液的水力传导性响应与水动力弥散系数有很大不同。通过固结试验确定了不同固结条件下的饱和导水率。(2)根据溶质浓度测定了日本火山灰土Andisol的溶质分散度。对于饱和扰动土，分散性随孔隙水流速的增大而增大，而对于较低含水率的扰动土，由于团聚结构，分散性减小。饱和原状土壤的分散性是扰动土壤的十多倍，且随观测深度的增加而增大。另一方面，非饱和原状土的分散性与扰动土的分散性更接近。饱和原状土壤中的流动和运移由于根槽等大孔隙的存在而变得不均匀，而这些大孔隙随着含水率的降低而变得空洞。(3)在室内和野外条件下，利用时域反射仪(TDR)对粘性土的含水率和电导率进行了深入的研究。为了准确估计水分含量和土壤溶液浓度，提出了具体的校准方法。

Water flow and solute transport in soils were intensively monitored in a laboratory soil column to investigate the role of clay in flow and transport in a soil. Following three major results were obtained in this study. (1) Response of hydraulic conductivity of clay to Na-Ca mixed solution were quite different between high-swelling Bentonite and Hydrodynamic dispersion coefficients for undisturbed and disturbed Japanese volcanic ash soils, Andisols, in a field and low-swelling Ariake clay. The saturated hydraulic conductivities for various solution conditions were determined based on consolidation experiments. (2) Solute dispersivities were determined based on solute concentration for a Japanese valcanish ash soil, Andisol. The dispersivity increased as the pore-water velocity increased for a saturated disturbed soil whereas it decreased for lower water contents because of the aggregated structure. The dispersivity for the saturated undisturbed field Andisols was more than ten times greater than for the disturbed soil, and increased with the observation depth. On the other hand, the dispersivity for the unsaturated undisturbed soil became close to that for the disturbed soil. Flow and transport in the saturated undisturbed soils become heterogeneous because of macro-pores such as root channels, while these macro-pores become empty as the water content decreases. (3) Water content and electrical conductivity measurements with Time domain reflectometry (TDR) were intensively investigated for clayey soils in laboratory and field condition. Specific calibrations were proposed for accurate estimation of water contents and soil solution concentrations.