Study On Effects Of Simulated Acid Rain On Acidification Of Four Types Of Typical Soils From The Three Gorges Reservoir Region

The releasing characteristics and mechanism of ions in four types of typical soils (yellow soil grey-brown purplish soil red-brown purplish soil red purplish soil), which were collected from the Three Gorges Reservior Region, were studied by simulated acid rain leaching of soil columns equipment indoor. And we also analysed the releasing law of the aluminum, the leaching characteristics of base ions, the change characteristics of pH value and electric conductivity of the leachate. On the other hand, the critical loads of the tested soils were also studied by using acid titration. The results were as follows(1) Under the condition of simulated acid rain, the pH value of the leachates first decreased and then increased. There existed a lowest point in the pH curve owing to the reduction of the releasing amount of base cations and the decline of the buffering capacity of the tested soils with acid rain leaching. After this point, the pH value increased slightly and then tended to the period of relative stability. (2) The electric conductivity of the leachates first increased and then decreased. An EC peak occurred during all leaching processes with the shape of the peak obviously different. In general, the higher the pH value and CEC content of the soil were the greater the electric conductivity of the leachate was. The electric conductivity of the leachate decreased in the order red-brown purplish soil>red soil>grey-brown purplish soil>yellow soil. (3) The leaching amount of aluminium in four types of typical soils increased with the decline of acid rain pH. The leaching quantities were low at pH≥3.50 levels but increased remarkably at pH2.50. Meantime, leaching of simulated acid rain changed the concentration of exchangeable aluminium in soil (except for red-brown purplish soil). These changes were more remarkable in soils with the pH decrease of simulated acid rain. (4) The releasing amount of base ions in four types of typical soils increased with increasing rain acidity especially when acid rain pH≤3.5. Leached nutrients from the tested soil decreased in the order Ca²⁺>Mg²⁺>Na⁺>K⁺. Acid rain destroyed the balance of multi-kinds of elements in soil. As a result, it led to the loss of some cations the reduction of base saturation degree and the decline of the buffering capacity of the tested soils. On the other hand, the higher the base saturation degree and Ca²⁺ and CEC content of the soil were, the bigger the buffering capacity of the soil was. The buffering capacity of four types of typical soils decreased in the order red-brown purplish soil>red soil>grey-brown purplish soil>yellow soil. (5) Acid rain caused the acidification of four...