1. MOE Key Laboratory of Surficial Geochemistry, Department of Earth and Planetary Sciences, Nanjing University, 163 Xianlindadao, Nanjing 210023, China
2. Department of Geography, University of South Africa, Pioneer Avenue, Florida 1710, South Africa
3. Key Laboratory for Salt Lake Geology and Environment of Qinghai Province, Qinghai Institute of Salt Lakes, Chinese Academy of Sciences, Xining 810008, China