At present,the situation of water pollution prevention and control is very serious in China.The total amount control of pollutants in water environment management is the core of the total amount control of administrative target,which is lack of correlation with water quality response.The coupling between pollutant discharge permit allocation and water environment carrying capacity(WECC)is insufficient.The regulation mechanism for allocation of point source discharge permits have not been solved.Therefore,this study takes Changxing County,Huzhou City,Zhejiang Province,a typical plain river network area in East China,as an example.Consider the relevant indicators of WECC(economy and society,pollution load,water resources,water environment,and water ecology),based on the"driving force-pressure-state-response-economic benefit(DPSRE)"model and water environmental capacity method,we constructed a collaborative assessment model for the quantity and state of WECC.Through the regulation of WECC and multi-objective optimization,the allocation of point non-point source discharge permits is realized,and we constructed a system of pollutant discharge permit allocation and regulation mechanism based on WECC.This study provided technical support for improving the scientific and refined level of pollutant discharge permit system,improving the quality of watershed water environment and achieving stable standards.The main conclusions are as follows:(1)Based on the DPSRE model framework,we constructed the evaluation index system of WECC in the plain river network area of East China,which is composed of five core functions(social economy,water resources,water ecological environment,land service function,and water management).It includes three driving force indexes(population density,GDP per unit land area,output tax of industrial output per unit industrial land),three pressure indexes(water consumption per 10,000 RMB of GDP,consumption of chemical fertilizer applied per unit cultivated areas,discharge volume of wastewater per unit industrial output value),four state indexes(water quality compliance rate of regional exit section,development and utilization ratio of water resources,average flow of control section,coverage rate of regional forest and grass),four response indexes(number of environmental protection professionals in 10,000people,urban domestic sewage treatment compliance rate,rural domestic sewage treatment rate,universalization rate of swipe card sewage),and two economic benefit indexes(output tax of per unit industrial water,output tax of per unit emission right).(2)In terms of the quantitative evaluation results of WECC,the WECC of different aquatic eco-functional zones in Changxing County was significantly different in 2018.The quantitative evaluation results of WECC in zone 4,6 were not overloaded,and the other zones were overloaded.Among them,the water environmental capacity of COD of zone 2,3,and 5 was overloaded,and the water environmental capacity of NH3-N of zone 1,2,3,5 and 7 was overloaded.The contribution rates of COD and NH3-N into the river are the highest in rural domestic sources,and the average contribution rate is 50.1%and 51.6%respectively.In terms of the evaluation results of the state of WECC,the WECC of each zone in Changxing County has an upward trend in different ranges from 2010 to 2018.Except for the state subsystem,each subsystem has different degrees of growth,among which the economic benefit subsystem has the greatest contribution to the WECC.By analyzing the evaluation index of WECC,it is found that the water quality of the monitoring section was not stable,the distribution of water resources was uneven,and the point source pollution was serious.It was the main factors affecting the WECC.The WECC was greatly affected by the water period,and the state was poor in the dry period,which was mainly affected by the water resources and the fertilization intensity.In terms of the collaborative evaluation results of the quantity and state of WECC,the WECC of Changxing County was only zone 4not overloaded,and the other zones are overloaded.The state and quantity of WECC in zone 3 were overloaded,and the quantity of WECC in zone 1,2,5,6 and 7 was overloaded.(3)By applying the constructed method system of pollutant discharge permit allocation and its regulation mechanism based on WECC to Changxing County,we founded that the distribution results of pollutant discharge permits in each zone of Changxing County were significantly different.The permitted emissions of COD in zones 1-7 were 220.7,-175.3,-310.5,600.1,-62.9,1762.0,386.3 t/a,and the permitted emissions of NH3-N were-25.3,-25.5,-47.3,50.4,-33.8,163.0,-3.8 t/a,respectively.Through the case analysis of zone 2,we founded that the output value tax is adjusted from 34.3%and 34.1%to 17%and 15%after using the combined performance method,compared with the traditional allocation method based on pollution contribution rate.After the distribution of point and surface source control,the total amount of COD distribution is reduced by 16.5%compared with the actual total emission,the output value is increased by 5.0%,and the tax revenue is increased by 7.9%.According to the research results,two-way regulation of WECC is carried out from the perspective of’emission reduction’and’capacity increase’,and policy recommendations were put forward.From the perspective of WECC,the research results of this paper provide a scientific basis for carrying out scientific and refined management of regional pollutant discharge permits.At the same time,it also provides a theoretical reference for incorporating non-point sources into the allocation of pollutant discharge permits.With the WECC as the constraint,the discharge permit allocation model based on the combination performance method provides technical support for the improvement and development of the discharge permit system. |