Research On Pollution Load-water Quality Response And Comprehensive Prevention And Control Of Qiuxi River Basin

Tuo River is a tributary of the Yangtze River and one of the important rivers in the hinterland of Sichuan Province.In recent years,the environmental capacity of Tuo River has been seriously inadequate and water resources are in short supply.The river basin has been moderately polluted in general,and the problem of total phosphorus pollution is particularly prominent.Therefore,based on the Tuo River Basin,Qiuxi River which is the tributary of Tuo River was selected,and the hydrodynamic module(HD)and the transport module(AD)of the MIKE 11 water quality model were used to establish the relationship between pollution load and water quality in Qiuxi River,and develop the research on the dynamic distribution of pollutant receiving capacity during the year.The relationship is used to explore comprehensive prevention control strategies under different regulation and control schemes which are of great significance for supporting the dynamic management of pollution control in Tuo River Basin.The main research content and research results of the paper are as follows:(1)Accounting of pollution load.By analyzing the pollutant concentration of the monitoring section of the Qiuxi River that are Falun section and Qiuxi estuary from 2009to 2018,it was found that the pollutant concentration was less than the III standard of Surface Water Environment Quality Standard(GB3838-2002)from 2012 to 2014 and in the remaining years,the pollutant concentration was the V and higher than V standard.The water quality of Qiuxi River was seriously polluted;the annual average values of COD and ammonia nitrogen concentrations showed an overall upward trend,but neither exceeded the limits of the III standard,and the average total phosphorus concentration reached the higher limit of the IV standard.And the change trend of annual average concentration of total phosphorus is similar to the change trend of water quality category,which is the main factor affecting the water quality of the river.The method of combining pollution production coefficient and river inflow coefficient is used to calculate the amount of total phosphorus pollution into the river in Qiuxi River.From the analysis of the total phosphorus of contribution of the point and non-point source pollution in Qiuxi River,point sources pollution,including urban life,sewage treatment plants,industry,accounts for 36%of the total.Non-point sources pollution,including rural life sources,non-point source loss in urban built-up areas,livestock and poultry breeding,agricultural planting,accounts for 64%of the total,and the pollution load into the river is mainly due to non-point sources contribution.In point sources pollution,it is mainly the source of urban living pollution;in non-point sources pollution,the main source of pollution is livestock and poultry farming.(2)Establish the relationship between pollution load and water quality in Qiuxi River.The hydrodynamic module(HD)and the transport module(AD)of the MIKE 11 model are used,and the measured hydrological data and water quality data of the Beidou hydrological station are used to rate and verify the model parameters.The simulation results show that the flow E_nsis 0.91,the average relative error of the total phosphorus simulation value is 14.14%,and the simulation error is small,which can better reflect the actual change law of the hydrodynamics and water quality of Qiuxi River.The model was used to calculate the contribution rate of each control unit to the estuary of Qiuxi River.(3)Setting regulation and control schemes.Based on the contribution rate,the total pollutant control target,and the Gini coefficient minimization model optimization results,combined with the dispatchable water sources in Qiuxi River,a variety of reduction control schemes for non-diversion,single diversion and combined diversion were formulated.The results show that the annual average value of total phosphorus concentration in the Qiuxi estuary meets the III standard in each simulation schemes;in the schemes of simultaneous reduction of point sources and non-point sources(without water transfer),the highest percentage of total phosphorus concentration decreases,indicating that the non-point sources pollution of Qiuxi River is serious,and the comprehensive prevention and control of Qiuxi River should be dominated by non-point sources;after only point source reduction and water transfer measures,the total phosphorus concentration exceeding the standard rate in the Heilongtan Reservoir water transfer scenario is the lowest,and it can be given priority in practical engineering applications transfer water from Heilongtan Reservoir.(4)According to the simulation analysis of the distribution characteristics and control schemes of point sources and non-point sources in Qiuxi River,it is found that water transfer measures is conducive to reducing the total phosphorus concentration of the Qiuxi estuary;for the comprehensive prevention and control of point source pollution,the focus should be on accelerating the construction of treatment facilities and the upgrading of standards,as well as the centralizing control of water pollution in industrial enterprises;for the comprehensive prevention and control of non-point sources pollution,the focus should be on strengthening the pollution control of livestock and poultry farms,promoting the reduction of chemical fertilizers and pesticides,and accelerating the comprehensive improvement of the rural environment.