Spatial distribution characteristics of water quality in Bailianjing Reach of Shanghai

The investigation on water quality of Bailianjing reach in Shanghai was carried out from April 2007 to April 2008.Six cross sections were chosen and the survey covered both the spring and neap tides throughout the year.Five water quality parameters which were dissolved oxygen(DO),permanganate index(CODMn),ammonia nitrogen(NH3-N),total nitrogen(TN) and total phosphate(TP),were used to calculate the single factor water quality identification index and the comprehensive water quality identification index(WQI) of 6 cross sections.As to the spatial distribution,water quality became worse when the river flowed into the residential areas.As to the time distribution,the water quality was worse in low water period than high water period and also worse during neap tide period than spring tide period.More than 90% of Bailianjing reaches exceeded standard Ⅳ according to the Environmental Quality Standard for Surface Water.The main pollutants were TN,NH3-N and TP.The water quality showed the best in August and September during the investigation period.