Water pollution and permissible pollution bearing capacity of water function zones in Nanjing reach of Yangtze River

Based on a five-year variation trend of the water quality of 18 water function zones in the Nanjing reach of the Yangtze River,the main pollution sources and the quantity of pollutants discharged into the river were evaluated and analyzed.Suggestions on permissible pollution bearing capacity and pollutant reduction of the water function zones are made.The results of the study show the following: The up-to-standard rates of 83.3% of the water function zones decreased with time during the period from 2005 to 2009.The monitored water quality in 83.3% of the water function zones in 2009 did not reach standards.The main pollution sources were the rivers connecting with the Yangtze River,where the discharge of COD and NH3-N were,respectively,65.7% and 49.9% of the total discharge into the river.The discharge of COD and NH3-N at industrial sewage outlets were,respectively,20.9% and 25.0% of the total discharge into the river.The permissible pollution bearing capacities of COD and NH3-N in the Nanjing reach of the Yangtze River were 6.59×104 tons per year and 0.26×104 tons per year,respectively.Pollutants need to be reduced in the water function zones,including five drinking water source regions,one reserved area,and three fishery,agricultural,and industrial water use areas.The pollutants in the drinking water source regions need to be reduced to as large degree as possible.The reduction rates of COD and NH3-N ranged from 87.0% to 99.0%,and 17.8% to 97.4%,respectively.