Temporal And Spatial Variation Characteristics And Evaluation Of Water Quality In The Yanhe River Basin

Located in the hinterland of Yan’an City,the Yanhe River is a first-class tributary to the Yellow River.It is the main supplier of freshwater resources in Yan’an City,and undertakes the main functions of flood control,drainage,and pollution in the area.In recent years,due to the reduction of natural runoff in the Yanhe River Basin and the increase of pollutant discharge,the capacity of the water environment is overloaded,the self-purification capacity of the water body is significantly reduced,and the pollutants in many monitoring sections have seriously exceeded the standard.Due to the deterioration of the water environment,the ecological environment is fragile.The biggest constraint to the sustainable economic and social development of Yan’an.This paper takes the Yanhe River Basin as the research object,and based on the Yanan River water quality data monitored by the Yan’an Environmental Monitoring Station from 2017 to 2020,selected dissolved oxygen（DO）,permanganate index(COD_Mn),five-day biochemical oxygen demand amount（BOD₅）,ammonia nitrogen（NH₃-N）,petroleum（Oils）,volatile phenol,chemical oxygen demand(COD_Cr),total nitrogen（TN）,total phosphorus（TP）,arsenic（As）,hexavalent chromium(Cr⁶⁺)and other 11 water quality indicators,using the principal component analysis method to analyze the water quality status and temporal and spatial changes of the Yanhe River Basin from three aspects:the temporal and spatial variation characteristics of the water quality indicators in the Yanhe River Basin,the comprehensive evaluation of the water quality in the Yanhe River Basin,and the analysis of the influencing factors of the water quality in the Yanhe River Basin.Comprehensive evaluation and research of characteristics.The specific results are as follows:（1）The temporal and spatial distribution of water quality in the Yanhe River Basin is quite different,and different monitoring sections in different years show different water quality variation laws.By analyzing the temporal and spatial variation characteristics of11 water quality indicators from two dimensions of time and space,it is found that the water quality of the Yanhe River Basin is the best in 2020,and the water quality in 2017and 2018 is relatively poor;the water quality of the upper reaches of the Yanhe River Basin is better than that of the middle and lower reaches,and the water quality of the monitoring sections of Ganguyi and Yangjiawan is the worst.（2）Principal component analysis was performed on 11 water quality indicators in the Yanhe River Basin from 2017 to 2020,and 4 principal components were extracted:ammonia nitrogen（NH₃-N）,total nitrogen（TN）,and total phosphorus（TP）in the first principal component.The index concentration is the main pollution factor affecting water quality;the index concentration of arsenic（As）and dissolved oxygen（DO）in the second main component is the main pollution factor affecting water quality;the five-day biochemical oxygen demand（BOD₅）index in the third main component Concentration is the main pollution factor affecting water quality;the index concentration of volatile phenol in the fourth principal component is the main pollution factor affecting water quality.（3）Principal component analysis was performed on 11 water quality indicators in 9sections of the Yanhe River Basin in 2019,and 4 principal components were extracted:arsenic（As）,hexavalent chromium(Cr⁶⁺),and total nitrogen（TN）in the first principal component.Dissolved oxygen（DO）index concentration is the main pollution factor affecting water quality;in the second principal component,the permanganate index(COD_Mn)and chemical oxygen demand(COD_Cr)index concentration are the main pollution factors affecting water quality;the third principal component The index concentration of total phosphorus（TP）is the main pollution factor affecting water quality;the index concentration of volatile phenol in the fourth principal component is the main pollution factor affecting water quality.（4）According to the comprehensive score ranking of principal component analysis,the water quality in the Yanhe River Basin from 2017 to 2020 is 2020>2019>2017>2018,and autumn>summer>spring>winter;From the perspective of spatial scale,the water quality status from excellent to poor is represented as Ma’anqiao>Shiyao Village>Shanglijiawan>Zhujiagou>lower reaches of Ansai City>Tanjia River>Yanjiatan>Yangjiawan>Ganguyi.（5）The influence of natural factors and human activities on water quality is complex and uncertain.Through the analysis of the influencing factors of water quality in the Yanhe River Basin,this paper finds that the water quality of the Yanhe River Basin is affected by climate,precipitation,land use structure,and the population and density of the basin.The common influence of various factors such as industrial structure and sewage discharge,among which domestic sewage and industrial wastewater discharge are the main sources of pollution in the Yanhe River Basin,and point source pollution has a greater impact on the water quality of the Yanhe River Basin.