Water Environmental Capacity Calculation And Total Amount Allocation Research Of Yongding Watershed In Hebei Section

Yongding River is one of the seven major river network systems in the Haihe River Basin.It is an important water conservation area and ecological barrier of the Beijing-Tianjin-Hebei region.As the mother river of Beijing,it has been regarded as the “the green ecological corridor of the west and the ecological barrier of the southwest of the capital city”.However,currently,the severe water related problems of excessive water resources extraction,river drying up and ecosystem degradation in the Yongding River Watershed have significantly restrict the sustainable development of socio-economic in the Beijing-Tianjin-Hebei Region.In this study,the Hebei district in the Yongding River Watershed was selected as the research area.Based on the water quality monitoring data from 2010 to 2016,and the single factor evaluation method was used to screen the total phosphorus(TP),ammonia nitrogen and chemical oxygen demand(COD)as the control factors.Furthermore,according to the hydrological data(2002-2016)of Yongding River Watershed,the water environmental capacity of five national-control and provincial-control sections of Zuowei,Laoyazhuang,Xiangshuibu,Shixiali and Bahaoqiao sites of Yongding River Watershed in Hebei Province were calculated by the Load duration curve(LDC),the technical method of the US Environmental Protection Agency(USEPA)which has been used to determin the Maximum Total Daily Load(TMDL).Besides,the output coefficient method was used to check computation of the control units' load based on the control unit devision in this study area.Finally,according to the comprehensive allocation and the rate of contribution allocation method,the total amount distribution was carried out via the economic,population and cultivated land use data of the study area and the TMDL control measures were proposed.The main conclusions are as follows:(1)The water quality of Qingshui River and Sanggan River are relatively good,the Yanghe River is seriously polluted,and the main pollutants are total phosphorus,ammonia nitrogen,chemical oxygen demand and biochemical oxygen demand.Taking the Bahaoqiao site as an example,the water environmental capacity of total phosphorus of the moist condition interval,mid-range flow interval and dry condition interval are 46.81 t/a,25.83 t/a,16.41 t/a,respectively.(2)Water environmental capacity of the watershed varies greatly on both spatial and temporal,and it is relatively higher in the downstream than that in the upstream area.Seasonally,the assimilative capacity is higher in summer and autumn than those of the spring and winter.The higher water environmental capacity has been observed in July.In October,November,January and February the water environmental capacity was lower,and such fluctuations were mainly due to the seasonal water flow changes and the adjustment of water facilities.(3)The main pollution in this study area is came from the non-point source pollution discharge.The main sources of the pollution discharge were dispersed livestock,poultry and crop farming.The point source pollution mainly comes from sewage treatment plants and large-scale livestock and poultry breeding.The priority control unites are C-011-002-04,C-011-001-03 and C-011-002-06 located in downtown Zhangjiakou,Xuanhua District and Xiahuayuan Districts.(4)The total phosphorus and COD loads need to be reduced and the pollution sources of aquaculture and plantation need to be focused on in the study area.