EFFECT OF ACIDIC DEPOSITION ON FORESTED ANDISOLS IN THE TAMA HILL REGION OF JAPAN

Acid deposition and its effect on andisols was investigated in the forest experimental station, the Rolling Land Laboratory, the Tama Hill region, central Japan. The annual volume-weighted mean pH value of open bulk precipitation was 4.8. The acidity of stemflow from coniferous trees was attributed to dry deposition of air pollutants. The acidic stemflow affected the chemical composition of the soil solution and the pH of soils around the coniferous trees. The concentration of aluminium in the soil solution was accompanied by nitrate which was provided by nitrification in the low soil pH range. The concentration of aluminium in the soil solution, which ranged from 0.02 to 0.12 mmol(c) liter(-1) is similar to the critical levels for the roots of the trees. Andisols in the surface horizon are acidified due to the atmospheric acid deposition, even though seepage from the catchment is still neutral.