Study On Simulation Of Water Quality And Calculation Of Water Environmental Capacity In Guangxi Xijiang River Basin

Guangxi Xijiang River Basin is part of the Pearl River Basin,including seven core cities:Nanning City、Liuzhou City、Wuzhou City、Guigang City、Baise City、Laibin City、 Chongzuo City and four extension areas:Guilin City,Yulin City,Hezhou City and Hechi City.With the development of the Xijiang Economic Zone in Guangxi,the amount of pollutant discharge of the river basin is still high,and the pollutants such as chemical oxygen demand and ammonia nitrogen polluted the water environment.The water environment carrying capacity are facing the risk of reduction,the whole basin of water environmental protection work is also facing greater pressure.However,the water pollution prevention and control work in the Xijiang River Basin of Guangxi still has the problems of fragment and extensive water management.It can not make comprehensive understanding of water quality protection in the whole basin,and can not make accurate prediction of water quality according to hydrological data.Therefore,from the perspective of the whole basin,the establishment of water quality model based on hydrological data,carried out based on the control unit under the basin water environment capacity calculation research,for the accurate evaluation of river basin water quality,accurate implementation of river basin water environment management strategy is of great significance.At the same time,it provides a strong theoretical guidance for the local government to prevent water pollution.On the foundation of comprehensive analysis of the status of watershed water quality and calculation of pollution,based on the basin water ecological function zoning and pollutant discharge characteristics,using ARCGIS technology to control the watershed control unit,determing the control unit based pollutant pollution interval;Based the design flow under 90% monthly assurance rate on QUAL2 K model,the river basin water quality modell is established.Calculate and research the water environment capacity,determine the water pollution capacity of the river basin,Carry out river basin pollutant reduction calculation and determine the amount of pollutant reduction in control unit and the administrative area.The main findings are as follows:1.From 2007 to 2015,the water quality of the Xijiang River Basin in Guangxi continued to improve.Under the situation of average annual water quality,the water quality of Grade I and II decreased,and the proportion of Grade III water quality increased obviously.The total number of sections is basically kept at 5% above andbelow,and the interannual variation is relatively stable.Under the condition of the worst water quality,there is no class I water quality,class II and III water quality is increasing,and class IV to the worst class V have a overall downward trend.from 2007 to 2015,the CODcr and NH₃-N have different degrees of excessive.2.The CODcr and NH₃-N emissions of Xijiang River in Guangxi are 736961 t 79591 t respectively.The CODcr and NH₃-N emission rates were 53.0% and51.9% respectively,and the non-point source CODcr and NH₃-N emission rates were 47.0% and 48.1% respectively.According to CODcr emissions from high t o low statistics in different cities:Nanning>Guigang>Bais>Liuzho>Guili>Chongzu>Wuzho>Hech>Laibi>Hezho>Yulin.The NH₃-N emissions from large to small are respectively:Nanning>Guigang>Guilin>Liuzhou>Hechi>Baise>Wuzhou>Laibin>Cho ngzuo>Hezhou>Yulin.3.It is predicted that by 2020,the CODcr and NH₃-N emissions of Xijiang River in Guangxi will be 1047645 tons and 104570 tons respectively.4.By ARCGIS,the watershed is divided into 73 control units,include 553 small Calculation unit.The simulation results show that the simulation results of QUAL2 K are better and the relative error of CODcr and NH₃-N is 0.68%¹0.96% and7.88%¹8.52%,respectively.5.The Quantity of the water environmental capacity of Xijiang River Basin in Guangxi is still large.CODcr and NH₃-N are 2768106.12 t/a and 229963.74 t/a respectively,But there is a large difference in the spatial distribution of capacity and overload in some areas.6.The reduction of CODcr and NH₃-N in Guangxi Xijiang River Basin are248970.51 t/a and 32284.08 t/a respectively.the reduction ratio are 23.76% and 30.87%respectively.In addition to Liuzhou City and Wuzhou City without cutting CODcr,the other cities CODcr reduction from high to low ranked is Guigang>Nanning>Guilin>Chongzuo>Hezhou>Baise>Hechi>Laibin>Yulin>Liuzhou>Wuzhou.The reduction of NH₃-N from large to small are respectively Guigang>Guilin>Hezhou>Liuzhou>Chongzuo>Hechi>Baise>Nanning>Wuzhou>Laibi>Yulin.