1. Department of Environmental Engineering, Texas A&M University–Kingsville, 700 University Boulevard, Kingsville, TX 78363, USA.
2. School of Environment, Tsinghua University, Beijing 100084, China.
3. School of Sustainability, Arizona State University, Post Office Box 872511, Tempe, AZ 85287, USA.
4. Northwest Institute of Plateau Biology, Chinese Academy of Sciences, 23 Xining Road, Xining 81008, China.