1. Key Laboratory of the Three Gorges Reservoir Region's Ecological Environment, Ministry of Education, Chongqing University, Chongqing 400030, P. R. China,
2. Key Laboratory of the Three Gorges Reservoir Region's Ecological Environment, Ministry of Education, Chongqing University, Chongqing 400030, P. R. China
3. School of Construction Management and Engineering, University of Reading, Whiteknigtes, PO Box 219, Reading, UK