RESPONSE OF 2 CHINESE FOREST SOILS TO ACIDIC INPUTS - LEACHING EXPERIMENT

The effects of acid deposition on cation release and key properties of two forest soils collected near Guiyang and Nanchang in southern Chin a were studied in leaching experiments. Rebuilt soil columns consistin g of three soil layers were exposed to five different leaching solutio ns, i.e. deionized water, two solutions with pH about 3.5 and two solu tions with pH about 4.3. Salts (CaSO4, MgSO4, and NH4NO3) were added t o one of the pH 3.5 and one of the pH 4.3 solutions. A slight adsorpti on of anions (SO42-, NO3- and Cl-) was found for both soils. The chang es in soil chemistry were generally largest in the top soil. In this l ayer exchangeable aluminium increased particularly when leached with t he most acid solutions, while exchangeable calcium decreased for these solutions. For the most acid solutions exchangeable aluminium increas ed also in the sub soils. For the Guiyang soil the leachate concentrat ions of all ions decreased initially, but then remained stable. Also f or the Nanchang soil most ion concentrations were quite stable except initially. However, for the most acid leaching solutions the changes i n the exchangeable pools in this soil were so large that concentration of aluminium increased and the concentration of calcium decreased aft er approximately 1/3 of the solution had passed through the column. In both soils the weathering rate of aluminium depended strongly on pH o f the input solution, while ionic strength was of little significance. However, the aluminium concentrations in leachates from the Guiyang s oil depended mainly on the ionic strength. The experiment indicates th at the top layer of these sails, which are representative for many are as in China, will be acidified if the emission of sulphur compounds in creases and/or the emission of basic compounds decreases. The leachate s from the soils are not likely to become seriously acidified in the n ear future, except if there is a substantial increase in emission of s ulphur compounds and a concurrent decrease in emissions of basic compo unds.