Changing characteristic and trend analysis of water quality of Qiandao Lake

The results of analysis on the comprehensive pollution index show that most monitoring items and sectional pollution indexes demonstrate a notable declining tendency,indicating that the water quality of Qiandao Lake is faced with a relatively low risk.The comparisons of comprehensive water pollution index among sections show that the sections of Jiekou,Hangtou Island and Baimufan,which represent the three main water sources of Qiandao Lake,are the most serious ones.The pollutants input through rivers are the primary threat of the water quality.Jiekou has the highest intensity of contamination input.Its index is significantly higher than those of other sections.The comparative analysis of the comprehensive pollution indexes of all monitoring items indicates the input of total N is the primary risk factor leading to the decline of water quality in the near future.The load ratio analysis of the comprehensive pollution indexes of all monitoring items,the indexes of total N,dissolved oxygen and potassium permanganate are the highest ones,with a total value up to 71% of the whole lake,and total N is approximately 49%,much higher than other items.The tendency analysis shows that the load ratio of total N presents a significant declining trend,and to some extent so do other items except fecal coliform.