1. State Key Laboratory of Urban Water Resource and Environment, Harbin Institute of Technology, Harbin 150090, P.R. China, School of Forestry, Northeast Forestry University, Harbin 150040, P.R. China, School of Energy and Environmental Engineering, Beijing University of Technology, Beijing 100022, P.R. China, and Department of Civil and Environmental Engineering, Stanford University, Stanford, California 94305-4020