Analysis Of Water Environment Factors And Assessment Of Water Environmental Quality In Heihe Basin

With the implementation of the Western Development strategy and the construction of the Silk Road Economic Belt,the development of northwest China has been accelerating.While population growed rapidly and production scale expanded continuously,the river of northwest China were polluted by pesticides,chemical fertilizers and some untreated industrial sewage.Water pollution has become a major obstacle to the economic and social development of northwest China.Bsaed on the investigation of the water environment factors of Hei River basin which included Babao River,Yeniugou,Beida River,Liyuan River,Hongshui River,Shandan River,Zhangye Wetl,Middle reach main sream,Ejina River and East Juyanhai,the water quality and nutrient status of Heihe River Basin were analyzed and discussed,which would provide basic data and theoretical basis for water environment management,water resources protection and sustainable utilization of Heihe River Basin.The main results of this study were as follows:(1)By the method of principal component analysis and factor analysis,the influence factors on water quality of Heihe River Basin in 2013 were pH,ammonia nitrogen(NH3-N),total nitrogen(TN),total phosphorus(TP),permanganate index(CODMn)in April,and NH3-N,TN,Chlorophyll a(chl.a),TP,CODMn in July,and TN,CODMn,NH3-N,TP,chl.a in December.The influencing factors on water quality of Heihe River Basin in 2014 were chl.a,TN,CODMn,TP,NH3-N,transparency(SD)in April,and TP,chl.a,CODMn,TN,conductivity(EC),NH3-N in July,and TN,TP,EC,CODMn,NH3-N,pH in December.The influencing factors on water quality of Heihe River Basin in 2015 were pH,NH3-N,TN,TP,EC in April,and TN,NH3-N,CODMn,chl.a,TP in July,and chl.a,CODMn,TN,SD,TP in December.The influence factoes on water quality of Heihe River Basin varied in different period.Generally,the main influence factors on water quality of Heihe River Basin were nitrogen and phosphorus nutrients which led to the change of the content of planktonic algae and other organic matter.(2)The grey correlation analysis method and BP neural network method were selected to evaluated the water quality of the Hei River Basin,The water quality of Baobao river,Yeniugou,Beida river,Liyuan river,Hongshui river,Shandan river,Middle reach main sream,EjinaRiver was??? class.The water quality of Zhangye Wetland was ? class because of aquatic plant biomass.The water quality of Dongjuyan lake which located in the end of the HeiheRiver Basin was V class because of nutrient and contaminant enrichment.The results of water quality evaluation were different between grey correlation method and BP neural network method.The evaluation results of BP neural network were more objective and accurate than that of grey correlation method(3)The nutritional status of Heihe River Basin was evaluated by comprehensive nutrition status index method and BP neural network method,the results showed that average nutrient index of Baobao river was 42.96,Yeniugou was 47.81,Beida river was 43.55,Liyuan river was 43.19,Hongshui river was 42.99,Shandan river was 43.41,Zhangye Wetland was 48.54,Middle reach main sream was 43.56,EjinaRiver was 43.60 and Dongjuyan lake was 82.18.The eutrophication status of Dongjuyan lake was severe eutrophication,while the total nitrogen content was high.The eutrophication status of ther watershed was mainly middle trophic level.The evaluation results of eutrophication were different between the comprehensive nutritional status index method and BP neural network method.Because the transparency of the Northwest Inland rivers such as the HeiheRiver did not fully reflect the state of eutrophication,the evaluation results of the comprehensive nutritional status index were conservative.The evaluation method of BP neural network could eliminate the influence of transparency,which was more closed to the actual situation compared with the comprehensive nutrition index method.