EUTROPHIC STATES AND INFLUENCE FACTORS OF LARGE AND MEDIUM-SCALED RESERVOIR IN HANGZHOU AREA

In order to understand the water environment of reservoirs,an investigation was conducted on the water quality in 17 large and medium-scale reservoirs of Hangzhou City,China.The results showed that the water quality of those reservoirs were not optimistic.According to a single factor index,the water qualities of three reservoirs met GradeⅡ water standards,two reservoirs met Grade Ⅲ,two reservoirs met Grade Ⅳ,three reservoirs met GradeⅤ and seven reservoirs were worse than GradeⅤ.The specific index determining the classes was total nitrogen in all cases.According to trophic state index,in the wet season two reservoirs were oligotrophic,thirteen reservoirs were in mesotrophication and two reservoirs were light eutrophication;in the dry season sixteen reservoirs were in mesotrophication and one reservoirs was in moderate eutrophication.Total nitrogen and total phosphorus were the main factors affecting eutrophication.The results of cluster analysis showed that the seventeen reservoirs were divided into three categories.Qinshan and Fuchunjiang reservoirs were identified as a class for the bad water quality;Tongshan,Xiayuan,Fengshuling and Yanjia reservoirs located in the upstream region of Xinan River and Xinanjiang reservoir were identified as the second class for the good water quality;the remaining ten reservoirs were identified as the third class.The reservoirs located in mountainous region had the best water quality,reservoirs near the town followed and reservoirs located near the city and downstream city had bad water quality.Different regions and different types of reservoirs had different pollution reasons.For different reasons we should implement corresponding countermeasures to prevent and control reservoir pollution.