Study Of Leaching Natures And Soil Chemical Characteristics Of Typical Forests Under Acid Rain Stress

Acid rain is one of the most serious environmental problems of our country. It can cause forests decline and even die. Guizhou is one of the provinces which have severe acid rain pollution in South China, therefore, it's very important to study the status quo and its influence to forest ecosystem of Guizhou, which is helpful to protect local forest resource and reduce damages to environment induced by acid rain.This paper took Longli ecological park as the study area to reveal acid rain's influence to local typical forests and their response. With the monitoring results of rainfalls, throughfalls, soil and soil water from April 2007 to December 2008, the paper analyzed chemical characteristics and variation tendency of acid rain, compared buffering capacity through cation leaching of typical forests, discussed soil acidification status and possible reasons. The main results included that as follows:1. Chemical characteristics and variation tendency of acid rain(1) Acid rain of study period had a frequency of over 70% and a worsen tendency, and it was typical sulfate style. (2) Occurrences of acid rain were higher in spring and lower in summer. (3) The wet depositions of sulfur and nitrogen did not exceed the critical loads estimated by the other studies.2. Buffering capacity through cation leaching of typical forests(1) pH values of precipitation increased obviously after getting through the crowns, and mixed wood had a better buffering effect than masson pine. (2) Concentration of most ions were obviously higher than that of rainfalls except NH⁴⁺, and cation separated out more than anion, which could induce acidification of crowns. (3) Crowns of masson pine and mixed wood had a certain absorption of NH⁴⁺ and NO₃^-, which could mitigate acidification of soil. (4) Acid rain induced nutrient ions such as Mg²⁺, K⁺ and Ca²⁺ to leach and lose. 3. Chemical characters of soil(1) pH values of different depth of soil declined 0.2¹.3 after acid rain, and concentration of harmful ions such as Al³⁺, Hg²⁺ and Pb²⁺ increased obviously. (2) Soil under both forests was acidic, and soil of masson pine was more acid. (3) Through neutralizing H+ and adsorbing SO42- and NO₃^-, soil could relieve acid rain's influence in a certain extent, and top soil had best capacity of neutralization. (4) The absorption capacity of SO42- of local soil was not excellent under the action of acid deposition in the perennial, but it did not damage local forest obviously because of the high concentration of Ca.