A study of the characteristics and mechanisms of soil acidification in the Dongting Lake region in Hunan Province,South China

Acid deposition and soil acidification occur more severely in the Dongting Lake region in Hunan Province, South China. Acid deposition appears to be seasonal.Regional differences show a close spatial correlation with soil acidification, whereas the extent of soil acidification depends on the content of electropositive ions. In severely acidified areas, soil acidification may occur at a depth of about 50 cm, and much Al dissolves out along with the soil acidification. There is a critical point on the curve of soil pH vs. the content of basic cations, S and N, which is corresponding to a pH of 8. In alkaline conditions, a large quantity of basic cations is dissolved owing to the hydrolysis of silicates and aluminosilicates. Hence the soil acidity that is due to the input of SO~2-4 and NO~-3 is neutralized. However, when the pH is below 7.25, the buffer system set up by acid and alkaline materials in soil is no longer effective.A little increase of acid material will rapidly trigger the soil acidification.