1. School of Environment Science and Spatial Informatics, China University of Mining and Technology, Xuzhou 221116, China
2. Engineering Research Center for Coal Mining Subsided Land and Goaf Treatment of Shandong, Jining 272100, China
3. Institute of Geography, Faculty of Science, Pavol Jozef Šafárik University in Košice, Jesenná 5, 040 01 Košice, Slovakia