ASSESSMENT OF WATER QUALITY IN THE CHISHUI RIVER BASIN DURING LOW WATER PERIOD

Chishui River is the only unexplored tributary of the Yangtze River and also the nature reserve of valuable and rare fish of the Yangtze River.Therefore,it is necessary to enhance the research on water environment protection of Chishui River.Because of the smaller water flow and poor self-purification ability of river during winter period,we chose to sample in winter season.37 samples covering the whole basin of Chishui River were collected and analyzed during the dry season in this study.We applied the box plot based on STATISTICA 9to show the distribution of various water quality indicators of the mainstream and the tributaries intuitively and then,the comprehensive water quality identification index was utilized to fully depict the general water quality of the Chishui River.The water quality parameters for all samples were determined,by which we got the variations of spatial distribution and the characteristics of the water quality.The results showed that the Chuishui River water quality was generally good.The comprehensive water quality index of the whole basin was 1.6and 1.5for the mainstream.For the tributaries,the water quality identification indices of Tongzi River,Gulin River and Xishui River were 1.5,1.7and 1.5.But Yanjin River got serious polluted,and the water quality identification index was3.2,the concentration of total phosphorus(TP)reached 0.6mg/L especially.The water quality evaluation results of each sampling point were excellent,except for the source.The water quality indices of the sampling points beyond the standard were Yudong Village(TN,DO),Linzhen Village(TP)and Yanjin River(TP).In the whole basin,the overall level of TN was higher,which was a potential index beyond the standard.As the most polluted watershed of the Chishui River Basin,the total nitrogen(TN)and CODcr in Yanjin River decreased significantly,but eutrophication indices such as total phosphorus(TP)and dissolved oxygen(DO)were deteriorating in recent years.The government should focus on the prevention and control,although the water quality of Chishui River basin was still at a relatively good level and the pollution sources were generally under control,and the government also need to pay heed to limit or reduce the emissions of urban sewage.To get how the water quality of Chishui River changes,we need further long-term monitoring.