Acidification Simulation,Forecast And Critical Load Calculation For Soils In Changsha

Soil acidification may. become a serious problem in Changsha because of long-term serious acid deposition. In order to understand the effect of acid deposition on soils in this region, Red Soil derived from Quarternary Red Clay and Red Soil derived from Slate have been selected as research objects. In the present paper, the MAGIC model with two soil reservoirs was selected to investigate long-term changes of base satuation (BS) in soils and that of alkalinity (Alk), pH, concentrations of Al~3+, SO4~2-, the sum of Ca~2+ and Mg~2+ in soil waters due to acid deposition for the two soils. Critical load of acid deposition has been calculated and sensitivity to changes in the model parameters have been analyzed. The model simulations indicate that long-term acid deposition has resulted in soil acidification in the region, especially in the upper horizons. The acidification of Red Soil derived from Quarternary Red Clay was more serious than that of Red Soil derived from Slate. According to the modeling results, decreases in pH about 0.25~0.4 pH unites and BS about 3.5~6% and Alk have occurred in the upper soils, the range of changes of Red Soil derived from Quarternary Red Clay was bigger than that of Red Soil derived from Slate. In the deeper soils, both pH and BS were quite stable for the two soils during the period of 1920 to 2000, demonstrating that these soils have a large acid neutralizing capacity. The changes that have occurred in soil waters in deeper horizons mainly increased concentrations of SO4~2-, Ca~2+ and Mg~2+ are not likely to be harmful. The chemical characters in deeper soils vary lightly but substantially in upper soil to assumed seven future deposition for the period of 2000 to 2060. Soil acidification will accelerate especially in the upper soils if deposition of SO42" increases or even if maintains similar to the present situation, pH, Alk and BS will decline continuously, but concentrations of Al~3+ will rise sharply. On the other hand, soil conditions will improve if a 30% to 40% reduction in SO42" deposition is achieved in the future. Critical load of acidification for Red Soil derived from Quarternary Red Clay and Red...