Variation Trend of Water Quality and Analysis of Specific Pollutants of Caohai Lakeof Dianchi Lake

Water quality index( WQI) was adopted to evaluate the water quality of Caohai Lakeof Dianchi Lake using the 10 years monitoring data of Caohai Lake in Dianchi lake from 2002 to 2011 on the basis of Quality Standard for Surface Water( GB3838- 2002) andDianchi Lake Local Evaluation Regulations on Water Environmental The results showed that the heavy metal index indicated a good water quality. The index decreased from 2004 to 2007. The water quality in terms of heavy metal was worst in 2007 during the ten years.The second kind of index scored from 72 to 92,which showed a serious pollution and unsecure status. The worst water quality occurred in the year of 2009. The second kinds of pollutants contributed most to the WOI and have become the major pollutants in Caohai Lake. The score of the third kind of index varied between 3 and 32,which showed a good water quality status. The nutrients were the major factor influencing the fluctuation of water quality.Total nitrogen and total phosphorus are the specific pollutants of Caohai Lake.