1. School of Geographical Sciences, Northeast Normal Univ., 5268 Renmin St., Changchun, Jilin Province 130024, China.
2. Professor, School of Geographical Sciences, Northeast Normal Univ., 5268 Renmin St., Changchun, Jilin Province 130024, China (corresponding author).
3. Lecturer, School of Geographical Sciences, Northeast Normal Univ., 5268 Renmin St., Changchun, Jilin Province 130024, China.