Characteristics And Mechanisms Of Ion Releases Of Several Soils Collected From Northern Guangdong Under Simulated Acid Rain

In this study, the releasing characteristics and mechanism of ions in three types of typical soils (calcareous soil,red soil,purplish) ,which were collected from northern of Guangdong on different mothers' rock, were studied by simulated acid rain leaching of soil columns equipment indoor. And we also analysed the leaching characteristics of base cation, the releasing law of the silicon and aluminium ,the leaching change of anion (SO42- NO3-) and the change characteristics of pH value of the leachate. The results were as follows:1. Under the condition of simulating acid rain, the content of base cations increasd with the increase of pH values of simulated acid rain and the leaching volume in the three types of soils. While their increasing degree were different respectively, when the pH values of simulated acid rain was over 3.6, the total releasing amount of base ions in the soils increased rather small with the increase of pH value; however,when the pH value was below or equal to 3.6, the total releasing amount of base ions in the soils increased significant with the increase of pH value. Leached .nutrients from the lysimeters decreased in the order Ca~2+>Mg~2+>Na~+>K~+, which was consistent with the content in the original soils, the concentration of Ca~2+ and Mg~2+ in the leachate increased with the increasing acidity of leached solution when the pH of leachate was less than 3.6. Ca~2+ in the base cation mainly played a buffering role.Soil acidification was influenced by simulated acid rain. In general, the higher the pH value and CEC content of the soil were, the greater the releasing amount of the base ions was, and the smaller soil acidification was affected by acid rain. The decrease of pH value in soil followed the order of calcareous soil>red soil>purplish soil, indicating that buffering capacity of calcareous soil to acid rain was the biggest, Owing to the calcareous soil contained abundant Ca~2+ and base saturation was higher than the other two soils significantly, its buffering capacity was relatively greater. While the purplish soil and red soil were less sensitive to acid rain. After the base cation reactions of soils were consumed, the soil began to enter the second buffering system (mainly the weathering of aluminate and silicate) to buffer acid rain in the course of weathering, the soil not only released the Si and Al, but also base cations such as the calcium, magnesium, potassium and sodium, etc.2. The experimental results indicated that the weathering rate increased evidently due to the decrease of pH value of simulated acid rain. The decrease of pH of simulated acid rain accelerated acidic hydrolysis of aluminate and silicate in soils, and resulted in massive release of Si and Al. While pH was lower than 3.6, the releasing amount increased. Othertimes, the variety is smaller. Meantime, the amounts of Si and Al increased with the volume of leaching...