Pedosphere 6(1): 11--22, 1996
ISSN 1002-0160/CN 32-1315/P
©1996 Soil Science Society of China
Published by Elsevier B.V. and Science Press
| Significance of ligand exchange relating to sulfate in retarding acidification of variable charge soils caused by acid rain |
| WANG Jing-Hua and YU Tian-Ren |
| Institute of Soil Science, Academia Sinica, Nanjing 210008 (China) |
| ABSTRACT |
| For the purpose of evaluating the role of ligand exchange of sulfate ions in retarding the rate of acidification of variable charge soils, the changes in pH after the addition of different amounts of HNO3 or H2SO4 to representative soils of China were measured. A difference between pH changes caused by the two kinds of acids was observed only for variable charge soils and kaolinite, but not for constant charge soils and bentonite. The larger the proportion of H2SO4 in the HNO3-H2SO4 mixture, the lower the calculated H+ ion activities remained in the suspension. The difference in H+ ion activities between H2SO4 systems and HNO3 systems was larger for soils with a low base-saturation (BS) percentage than those with a high BS percentage. The removal of free iron oxides from the soil led to a decrease in the difference, while the coating of Fe2O3 on a bentonite resulted in a remarkable appearance of the difference. The effect of ligand exchange on the acidity status of the soil varied with the soil type. Surface soils with a high organic matter content showed a less pronounced effect of ligand exchange than subsoils did. It was estimated that when acid rain chiefly containing H2SO4 was deposited on variable charge soils the acidification rate might be slower by 20%-40% than that when the acid rain chiefly contained HNO3 for soils with a high organic matter content, and that the rate might be half of that caused by HNO3 for soils with a low organic matter content, especially for latosols. |
| Key Words: acid rain, ligand exchange, soil acidification, sulfate adsorption, variable charge soil |
| Citation: Wang, J. H. and Yu, T. R. 1996. Significance of ligand exchange relating to sulfate in retarding acidification of variable charge soils caused by acid rain. Pedosphere. 6(1): 11-22. |
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