Role of clay in water flow and solute transport in soils

点击翻译按钮获取中文摘要

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.