Characteristics Of Water Quality Changes In The Shaanxi Section Of The Weihe River Main Stream And Evaluation Of The Effect Of Its Control Policy Implementation

The Weihe River is a key river in the Guanzhong region of Shaanxi Province,as known as the Mother River of Shaanxi.However,the water quality of the main stream of the Weihe River in the Shaanxi section has deteriorated sharply since the 1980s,along with the rapid development of the economy and urbanization in the Guanzhong urban agglomeration.Since 2004,the Shaanxi Provincial Government has issued multiple policy documents on water pollution control in response to the the Weihe River water pollution,and has invested a large amount of manpower,material resources,and financial resources to control the Weihe River water quality.After more than ten years running action,the water quality of the Weihe River has significantly improved.The analysis and evaluation of the water quality of the Shaanxi section of the Weihe main stream and the effects of the implementation of these policies can provide an important model and reference for river management.In this dissertation,we widely collected relevant information and data on the Shaanxi section of the main stream of the Weihe River,analyzed the regional pollutant emissions and changes in water quality,conducted an evaluation system of Weihe River health,and evaluated the implementation effect of relevant policies for Weihe River controlling action.The main conclusions were following.（1）The total emissions of ammonia nitrogen（NH₃-N）and chemical oxygen demand（COD）in Xi’an decreased significantly between 2005 when the Weihe River control action began and 2020.Between 2011 and 2020,the total emissions of NH₃-N and COD in Baoji,Xianyang City and Weinan City showed an overall decreasing trend.Among the pollution sources,the largest contributor to the pollution of the Shaanxi section of the Wei River main stream is urban domestic sources,followed by agricultural surface sources and rural domestic sources;the smallest contributor is industrial sources.（2）From 1991 to 2020,the concentration and total amount of NH₃-N and COD in the Linjiacun and Changxingqiao sections in upper stream,showed a decreasing trend along with time;The NH₃-N and COD concentrations at the sections of Xianyangtieqiao,Xinfengzhenqiao,and Tongguandiaoqiao show a trend of first increasing and then decreasing curve with most turning points between 2002 and 2005,as well as the total emissions between the sections.Both before and after treatment,the main stream of the Weihe River exhibits a relatively low concentration of pollutants in high water years and a relatively high pollutants concentration in low water years.For the total amount of pollutants,the main stream of the Weihe River showed a relatively high total amount of pollutants in high water years and a relatively low total amount of pollutants in low water years,from 1991 to 2003 before the treatment.However,there was no significant difference in the annual average of total COD and NH₃-N,in the years 2004to 2020 after governance.（3）A total of 10 index were selected from 5 aspects to construct the Weihe River health evaluation index system,including hydrology,water quality,biology,physical structure,and social service function.From criterion layer,the scores of 5 aspects indexes layer,the scores of ecological flow satisfaction,water sediment ratio,riverbank stability,wetland retention rate,water quality,fish biological retention index,water resource development and utilization rate,flood control capacity,and water supply capacity were 63.33,100.00,57.38,64.00,70.00,60.64,51.00,98.21,and 88.75,respectively.The overall score of the Weihe health was 67.51 with a healthy state in2020.（4）Based on the Pressure-State-Response（PSR）framework,an evaluation system water pollution control for policy implementation effect has been established for Weihe River.From 2004 to 2020 year that water pollution control policies were carried out,the overall score of the Weihe River was 66.06,with scores of 44.29,55.37,52.27,67.06,78.85,and 80.47 for the indexes of total regional pollutant discharge,industrial pollution discharge intensity,urban pollution discharge intensity,main stream water quality status,pollutant total reduction and compliance rate,and policy water quality target achievement rate,respectively.Within the Shaanxi section of Weihe main stream,Xi’an scored 71.69,Weinan 63.56,Baoji 62.30,and Xianyang 60.79.The results of water pollution control effectiveness for the Weihe River in three periods from 2004 to2010 year,2011 to 2014 year,and 2015 to 2020 year were 45.26,58.17 and 87.64,respectively.The water quality improvement was relatively significant from 2015 to2020,and the scores were closely related to water quality parameters,indicating that the policy"Shaanxi Provincial Water Pollution Prevention and Control Work Plan"had a significant effect at that time.