2003 年 36 巻 4 号 p. 464-470
Acidic precipitation is a worldwide problem. Acids result from human activities, such as coal burning and the use of internal combustion engines. Though surface soils work to neutralize acidic precipitation and maintain land water at neutral levels, the environmental impact of acidic precipitation on the neutralization ability of soil has not been clarified. In this paper, the effects of acidic precipitation on the neutralization ability of the soil were experimentally examined in batch and column reactors with acidic solutions as the artificial acidic precipitation. Soil was collected in the Hokuriku area, located in the central part on the Japan-Sea side of Japan.
On that coastal area, winter precipitation contains not only high amounts of acidic components, but also high concentrations of calcium and sodium ions derived from the sea. It was found from experimental results that calcium ions disturbed the neutralization ability of soil, but sodium ions did not. In this paper, the neutralization ability of soil was also assessed by a method based on the chemical equilibrium analysis of the relationship between the concentration of metal ions and pH values in the aqueous phase. The assessment suggested that calcium ions in precipitation prolonged the neutralization ability of soil.
Carbon dioxide residing in small spaces in the soil was confirmed to enhance an increase in pH during the neutralization reaction. The existence of carbon dioxide was also found to promote the neutralization ability of soil. To elucidate the life-time neutralization ability of soil in respect of acidic precipitation, the effect of carbon dioxide residing in small spaces in soil cannot be neglected. This indicated that to achieve the aims of the present study, analyses of the solid, liquid and gas phases were required.
