Hydraulic Conductivity of an Allophanic Andisol as Affected by Solution pH
- T. Nakagawa * and
- M. Ishiguro
Recently, acid precipitation problems have become serious in many regions of the world. The adverse effects of acid precipitation on soils are also feared. In this study, our objective was to determine the effect of inflowing solution pH on saturated hydraulic conductivity (K). The K values were determined at a constant hydraulic gradient in columns packed at a dry bulk density of 0.51 Mg m−3. Influent solutions with the same electrolyte level (1 molc m−3) were prepared at pH 3, 4.2, 5.7, 10, and 11, respectively. The K values decreased when the influent solutions were pH 3 and 11. The K values at 38 pore volumes of an effluent decreased to ≈0.067 of the initial K0 at pH 3, and ≈0.25 of the initial K0 at pH 11, respectively. Measurements of dispersion by optical absorbance method were also carried out. Clay dispersed at low pH (pH < 4.5) and high pH (pH > 10). The structure of the soil columns when K was reduced were visually inspected after K measurements. Those aggregates at the upper portion (≈1 mm thickness) of the soil column seemed to be destroyed by dispersion of clay. It became clear that acidic or alkaline solution decreased permeability of the allophanic andisol. Such a reduction of permeability may significantly change the water balance in a field.
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