1. Key Laboratory for Environmental Pollution Prediction and Control, Gansu Province, College of Earth and Environmental Sciences, Lanzhou University, Lanzhou 730000, P. R. China
2. Laboratory for Earth Surface Processes, College of Urban and Environmental Sciences, Peking University, Beijing 100871, P. R. China
3. Helmholtz-Zentrum Hereon, Institute of Coastal Environmental Chemistry, Geesthacht 21502, Germany