1. Department of Crop and Soil Sciences, and Environmental Science and Policy Program, Michigan State University, East Lansing, Michigan 48824, Department of Crop, Soil, and Environmental Sciences, University of Arkansas, Fayetteville, Arkansas 72701, U.S. Geological Survey, Box 25046, MS 408, Denver Federal Center, Denver, Colorado 80225, and School of The Environment, State Key Laboratory of Pollution Control and Resource Reuse, Nanjing University, Nanjing, 210093, People's Republic of China