1. Beijing Normal Univ.; Beijing People's Republic of China
2. National Soil Erosion Research Lab.; USDA-ARS; 1196 SOIL Bldg., Purdue Univ. West Lafayette IN 47907-1196 USA
3. Open Research Lab. of Environment Change and Disaster of the State Education Commission; Beijing People's Republic of China
4. Institute of Soil and Water Conservation, Chinese Academy of Sciences; Yangling Shaanxi People's Republic of China