Earth Science Frontiers ›› 2008, Vol. 15 ›› Issue (6): 163-168.
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1School of Earth and Space Sciences, Peking University, Beijing 100871, China
2Beijing Municipal Research Institute of Environmental Protection, Beijing 100037, China
3Institute of Agricultural Resources and Regional Planning, Chinese Academy of Agriculture Science, Beijing 100081, China
4School of Water Resources and Environment, China University of Geosciences(Beijing), Beijing 100083, China