1. Key Laboratory of Arable Land Conservation (Middle and Lower Reaches of Yangtse River), Ministry of Agriculture and Rural Affairs, College of Resources and Environment, Huazhong Agricultural University, Wuhan 430070, P.R. China
2. Department of Chemistry, University of Wisconsin, Madison, Wisconsin 53706, United States
3. Departments of Soil Science, Civil & Environmental Engineering, and Chemistry, University of Wisconsin, Madison, Wisconsin 53076, United States