Water Environment Assessment And Analysis Of Pollution Sources In The Upper Reaches Of Lijiang River Basin

The research on the water environment and pollution sources of Lijiang River is very important for the ecological environment protection of Lijiang River.This paper analyzes the water quality changes of multiple sections by using the hydrological and water quality data,in order to comprehensively evaluate the water environment of the upper reaches of Lijiang River,and analyze the emissions and contribution rates of different industries and pollution sources.The completion of this study can provide some reference for water environment protection,pollution source control and management in the upper reaches of Lijiang River Basin.The main contents of this paper are as follows: first,the water environment quality of the main tributary section in the upper reaches of Lijiang River Basin in recent years（2015-2020）is evaluated,and its changing characteristics and trends are analyzed;19 monitoring points of main and tributaries are set up in Guilin urban reach,which are used for one year of intensive monitoring（October 2019-2020.10）,and the spatial and temporal characteristics of urban water quality are analyzed.Second,the upper reaches of Lijiang River Basin are divided into 11 basins by Arc GIS.According to the relevant statistical data and estimation methods,the pollution discharge and inflow of COD,NH₃-N,TN and TP in each sub watershed are calculated.Third,the point source and non-point source load of Lijiang River section are divided based on the digital filter and runoff segmentation.The main conclusions are as follows（1）The overall water environment quality of the main stream section of Lijiang River is good.From 2015 to 2020,the four monitoring sections of dabutou,Damian,Guilin hydrologic station and Mopanshan reach the class II water standard.In recent years,the water environment quality of the main monitoring sections of dabutou,Damian,Mopanshan and Guilin hydrologic station continues to improve.The water quality of some tributaries of Nanxi River and Xiaodong River exceeds the standard.From the change of water quality along the river,there is no significant change in the concentration of water pollutants from dabutou section to Damian section,and the comprehensive pollution index of water quality from Damian to Mopanshan shows an upward trend along the river.（2）According to the discharge of COD,NH₃-N,TN and TP,the calculation results show that non-point source pollution is the main factor causing the pollution of Lijiang River Basin,accounting for about 70%-80%;the major industries are rural life,urban life,planting and livestock breeding.Urban living source is the main source of pollution emission in urban areas such as Wayao basin,Nanxi River basin,Taohua River basin and Qixingqu basin.（3）The results of point source and non-point source segmentation based on digital filtering method and runoff segmentation method（taking Mopanshan as an example）show that the proportion of non-point source load of TN is 72%-73%;the proportion of non-point source load of NH₃-N is 74%-80%;the proportion of non-point source load of TP is 74%-75%.It is basically consistent with the statistical results of the discharge of pollution sources and the amount of water entering the river,that is,the pollution of Lijiang River basin is mainly caused by non-point sources.