CHEN Lu-hao1,JIANG Chang-sheng1,2,WU Yan1,YUAN Xue1,2(1.Key Laboratory of Eco-environments in Three Gorges Reservoir Region(Ministry of Education),College of Resources and Environment,Southwest University,Chongqing 400715,2.Chongqing Engineering ResearchCenter for Agricultural Non-point Source Pollution Control in the Three Gorges Reservoir Area,Chongqing 400716)