国家自然科学基金No.51009080,51209123;三峡库区生态环境教育部工程研究中心开放基金No.KF2013-05 Supported by the National Natural Science Foundation of ChinaNo.51009080,51209123 and the Open Fund of Engineering Research Center of Ecoenvironment in Three Gorges Reservoir Region of Ministry of EducationNo.KF2013-05