Study On The Water Environment Capacity And Total Pollutant Control In The Mainstream Of Liaohe River

Water environmental quality is not only affected by the total amount of pollutants into the river,but also closely related to the natural water inflow.Under the dual influence of human activities and climate change,the annual runoff of rivers in northern China has been declining obviously,and the problem of water resource shortage has become more prominent.The fluctuation of water environment quality caused by this has attracted the attention of scholars.In this paper,the main stream of Liaohe River is taken as the research object.According to the fluctuation of water environment quality,the total amount control under different hydrological conditions is studied to provide guidance and basis for the total amount control of pollutants and water quality management,and to achieve the purpose of continuous improvement of water quality of rivers entering the sea.Firstly,the water environment quality of the main stream of Liaohe River was analyzed to grasp the water quality status quo.Secondly,the point source and non-point source pollution load in the control unit are calculated and the main sources of pollutants are analyzed.The dynamic water environment capacity accounting in the period of abundant,flat and dry water in the control unit was carried out again to provide the basis for the total pollutant control.Finally,the load duration curve method is used to calculate the allowable load fluxes of pollutants in the basin under different hydrological conditions,and the total amount control target is put forward to better guide the water environment management in the basin.The main research results are as follows:（1）The representative water quality monitoring sections on the main stream of Liaohe River are selected to analyze the water quality change trend and evaluate the water quality status.The selected indicators for water quality evaluation were permanganate index(COD_Mn),five-day biochemical oxygen demand（BOD₅）,ammonia nitrogen（NH₃-N）,chemical oxygen demand（COD）and total phosphorus（TP）.The analysis results showed that the pollutant concentration in the upstream Sanhetun section reached the peak in 2018,and then decreased.The exceeding pollutants in each section were mainly COD_Mn,COD,BOD₅and TP,and the exceeding periods were mostly concentrated in the normal and dry periods.The exceeding sections were mainly Sanhetun,Mahushan and Panjin Xing’an.（2）The COD and NH₃-N pollution loads of the direct discharge of industrial enterprises,the tail water of sewage treatment plants,rural household pollution and farmland runoff pollution of each control unit in the main stream confluence area were calculated according to the statistical data of pollution sources in 2018 and the statistical Yearbook.The results showed that the non-point source pollution accounted for more than 60%of the pollution load in each control unit,and the farmland runoff was the main source of non-point source pollution.（3）Based on the determination of water environmental capacity calculation parameters such as water quality target,design flow rate and velocity,the water environmental capacity of each control unit was calculated by using segment tail control method.The results showed that the annual ideal water environmental capacity of COD and NH₃-N was 107691.7t and4495.2t,respectively,and the ideal water environmental capacity of the Liaohe River was relatively large in the wet season,accounting for 43%～75%of the annual ideal water environmental capacity.（4）Combined with the water quality objectives and daily average flow data of Sanhetun,Mahushan and Hongmiaozi sections,the flow duration curves and load duration curves of each section were constructed.The allowable load fluxes of pollutants in different hydrological years were determined according to different flow duration intervals,and they were distributed to each month and each season in the year.