SEASONAL CHANGE OF NITRATE AND SULFATE ANIONS IN THE ELUTED WATER FROM SURFACE SOIL WITH RELATION TO ACID-RAIN

Since 1985, the 40% to 50% of rain water was acid rain whose pH value showed lower than 5.00, in the data obtained at north district in Nagoya where our institute is located. The concentration of nitrate and sulfate anions in the rain water and eluted water taken from underground at 15 cm have been measured continuously. The relationship of these anions between rain water and eluted water was discussed on the data taken from June 1989 to June 1990. An average pH value of rain water was 5.18 for 69 rain falls. The rain water samples whose pH was lower than 5.00 were obtained on 34 rain falls and those whose pH was higher than 5.00 were obtained on 34 rain falls. The sample soil tested was taken from the garden of our institute as city garden soil, and forest soil, sea coast sand, and river bed soil were also tested in comparison with city garden soil. It was observed that most hydrogen ion put into the soil by rain fall was neutralized with the soil buffer action, and the concentration of hydrogen ion in the eluted water seemed to be regularized by the chemical equilibria between eluted water and each soil. On the other hand, the nitrate and sulfate anions showed dynamic seasonal change in the eluted water from city garden soil. The concentration of these anions in the eluted water decreased in spring and summer, and increased in autumn and winter. It depends on the growth of trees and grasses in the tested soil box. Such seasonal change of nitrate and sulfate anions in the eluted water must be considered as one of the factors, when a protecting technique is performed against acid rain damage to the plants.