基金The research project was financially supported by the Foundation of Visiting Scholars under the Ministry of Education, Key Laboratory for the Controlling Engineering of Southwestern Resource Developmerct, Environment and Calamity, Chongqing University (Grant No. 3 [2001] ) Document issued by the Department of Education and Technology the Scientific Research Project of Guizhou Provincial Department of Education (Grant No. Qian Jiao Ke 2001016).