1. Key Laboratory for Environmental Pollution Prediction and Control, Gansu Province, College of Earth and Environmental Sciences, Lanzhou University, Lanzhou 730000, P. R. China
2. School of Water and Environment, Chang’an University, Xi’an 710054, Shaanxi, P. R. China
3. Key Laboratory of Subsurface Hydrology and Ecological Effect in Arid Region of the Ministry of Education, Chang’an University, Xi’an 710054, Shaanxi, P. R. China
4. College of Agricultural and Forestry Economics & Management, Lanzhou University of Finance and Economics, Lanzhou 730000, P. R. China
5. School of Public Health, Chengdu University of Traditional Chinese Medicine, Chengdu 610000, P. R. China
6. Laboratory for Earth Surface Processes, College of Urban and Environmental Sciences, Peking University, Beijing 100871, P. R. China