Spatial-temporal Differentiation Of Water Environmental Factors In Qingshui River Basin

Ningxia was one of the six provinces and regions with severe water shortages in China.Water played an important role in the social and economic development of Ningxia.In recent years,with the development of science and technology and the progress of industrialization,a large number of sewage and wastewater discharged,which resulted in the deterioration of the water environment quality.In April,July,and November of 2018 and 2019,based on the date of water environment factors in the Qingshui River basin,which including 12 small watershed such as upstream,midstream,downstream,tributary Zhongweiwupai,Shuangjingzigou,Xianmahe River,Zhonghe River,Xihe River,Dongzhihe River,Jingou,Shayangou,Zhesigou,the spatial and temporal distribution characteristics of water environmental factors were analyzed.The main environmental factors affected the water quality of Qingshui River basin were analyzed and screened by principal component analysis and factor analysis.The method of comprehensive pollution index,grey correlation and fuzzy comprehensive evaluation were used to evaluate the water quality of Qingshui River basin.Based on the selected major water environment factors,the GM(1,1)model was applied to predict the change trend of the water environment factors of Qingshui River basin in July,November 2019 and 2020.The research results would provide some theoretical basis for the comprehensive management of water environment in Qingshui River basin.The main results of this paper were as follows:(1)Based on the analysis of the spatial and temporal distribution of water environment factors in the Qingshui River Basin,some water environment factors showed obvious seasonal changes.pH,suspended solids(SS),nitrate nitrogen(NO3-N),nitrite nitrogen(NO2-N),total phosphorus(TP),orthophosphate(PO4-P)reached their maximum values in July and the values in April were relatively small.Electrical conductivity(EC),chlorophyll a(Chl.a),ammonia nitrogen(NH3-N),permanganate index(CODMn),and chemical oxygen demand(CODcr)reached their maximum in July,and the values in November were relatively small.Dissolved oxygen(DO),total nitrogen(TN),and five-day biochemical oxygen demand(BOD5)reached their maximum in November,and then presented an increasing trend.Fluoride(F-)reached its maximum in November Value,relatively small in July.(2)Principal component analysis and factor analysis were used to analyze the water environmental factors in the Qingshui River Basin.Five,four,five principal components were respectively extracted from the water environment factors of the Qingshui River Basin in April,July and November.According to the ranking analysis of the comprehensive scores of various water environmental factors,TN,NH3-N,CODCr,F-and CODMn were the main factors that had the greatest impact on the water quality of Qingshui river basin.According to the ranking analysis of the comprehensive scores of twelve small basins in qingshui river basin,the higher pollution degree was mainly distributed in the middle and lower reaches of qingshui river basin,which were mainly mainly Shuangjingzigou,Jingou,Shayangou and Zhesigou.(3)The method of comprehensive pollution index,grey correlation and fuzzy comprehensive evaluation were used to evaluate the water quality of Qingshui River basin.In terms of the seasonal variation trend,the main pollution degree of Qingshui river was ranked as July,April and November,when F-was not involved,while it was ranked as November,July and April when F-was involved.The water quality of Qingshui River basin gradually deteriorated when F-was involved.The water quality of downstream,Shuangjingzigou,Jinggou,Shayangou,and Zhesigou were relatively poor in Qingshui River,which was at class ?.The water quality of the upper steam,Zhonghe and Xihe were good in Qingshui River,which was at ???.When comprehensive pollution index method,grey correlation method and fuzzy comprehensive evaluation method were used to evaluate water quality,the evaluation results would be different,among which the fuzzy method was more objective.(4)By method of GM(1,1)model,the trend of TN,NH3-N,CODcr,F-and CODMn were predicted in Qingshui River.From July 2019 to November 2020,the content of TN in the whole river basin would decrease slowly,which would be at class ???.The content of NH3-N would decrease,which would be at class ???.The content of TP would decrease,which would be at class ??? and would not exceed the standard.The content of BOD5 would decrease,which would be at class ???,while it would be higher and would be at class ??? in some small watershed.The content of CODcr would decrease,which would be at class ??? in middle stream and Zhesigou,while it would be at class ??? in other small watershed.The content of F-would increase,which would be at class ??? in upper stream,Xianmahe and Xihe,while it would exceed class V in other small watershed.In the future,the control measures of TN,NH3-N,CODcr,and F-should be strengthened.