DELINEATION OF POLLUTION CONTROL UNITS IN TYPICAL CASE AREA IN THE TAIHU LAKE BASIN AND ITS OVERLOADING RATE OF WATER ENVIRONMENT

The pollution control units are the base of the water quality targets management in basin scale.According to the protection requirements for the Taihu Lake and the Taihu Lake basin characteristics,the pollution control unit delineation system in the Taihu Lake basin was discussed.The pollution control unit delineation principles mainly include the principle of aquatic ecoregion being the basis,principle of river integrity,principle of management and operational feasibility,principle of including the most point and nonpoint sources of pollution,principle of trying to include the existing water quality monitoring section,etc.The main indicators of the pollution control unit delineation mainly include the subwatershed,level III aquatic ecoregion,distribution pattern and flow direction of river system,pollution source,water quality monitoring section,county and township level administrative boundaries.And the control unit delineation method is mainly the GIS spatial analysis.In this paper,Huzhou City and some places in Anhui Province,which are the upper reaches of Taihu Lake basin and are characterized by the hills and mountains and plains landscape,were selected as the case study area.In support of the various data,and with the help of techniques of spatial analysis and expert judgment,the study area was divided into twelve pollution control units.After several rounds of consultation and feedback,including experts' advices,government officials' comments and the local validation of field visits as well as the application in the test of water quality target management,the results showed that the pollution control units have good scientific value and operational use.Moreover,the overloading rates of water environment in water pollution control units were calculated,and the result showed that the COD,NH4-N,TN and TP pollution load overloaded the capacity of water environment in various control units.