1. State Key Laboratory of Environmental Criteria and Risk Assessment, Chinese Research Academy of Environmental Sciences, Beijing 100012, P. R. China
2. Institute of Water Ecology and Environment, Chinese Research Academy of Environmental Sciences, Beijing 100012, P. R. China
3. College of Water Sciences, Beijing Normal University Beijing 100875, P. R. China
4. Department of Civil and Environmental Engineering, University of California, Berkeley, California 94720-1710, United States