Abstract
When the soil contains a substantial amount of pH‐dependent charges, pH strongly influences hydraulic conductivity. Adverse effects of acid rain and chemicals on soils have been observed, but few studies have focused on hydraulic conductivity change due to pH. Changes to the saturated hydraulic conductivity (K) of allophanic andisol (volcanic ash soil), which has a substantial amount of pH‐dependent charges, during dilute acid leaching were examined in this study. K was determined at a constant hydraulic gradient in soil columns. Influent solutions of HNO3 and H2SO4 were prepared at pH 3 and 4. Tensiometer pressure potential and pH distribution in the soil columns were measured. Clay dispersion was measured by optical transmission and soil buffer capacity was evaluated from acid titration curves. K decreased during HNO3 leaching but increased during H2SO4 leaching. Because of the high buffer capacity of the soil, the influence of acid leaching on the soil structure was significant only at the soil surface. Soil dispersion was observed only in HNO3 solution. No dispersion was observed in H2SO4 solution because of the strong specific adsorption of SO2−4 The swelling and dispersion of the soil at the surface layer caused the decrease in K during HNO3 leaching, while these processes were prevented in H2SO4 leaching.
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