Study On Water Ecological Security In The Core Water Source Area Of The Middle Route Of "South-to-north Water Diversion Project"

The"South-to-North Water Diversion"mid-line project has exerted tremendous economic and social benefits in water-receiving areas such as Beijing,Tianjin,Hebei,and Henan since the water was opened.However,the water source area of the water delivery project is facing a series of ecological and environmental problems such as water pollution and biodiversity reduction,which threaten the smooth operation of the"South-to-North Water Diversion"mid-line project to a certain extent.Shiyan City is located in the core water source area of the"South-to-North Water Diversion"mid-line project,and its annual water transfer is close to 50%of its total water resources.In recent years,the industrial and agricultural development of Shiyan City has achieved remarkable results,and the population has increased significantly.The tasks of rural revitalization and urban development in Shiyan City are still very arduous,which will inevitably increase the consumption of water resources.The water ecological security of Shiyan City is of great significance to the sustainable development of the water source area and the water-receiving area of the"South-to-North Water Transfer Project"mid-line water delivery project.The In VEST model was used to calculate the water production and water conservation in Shiyan City from 1980 to 2018.Considering the ecological water demand in the river and the current water consumption in Shiyan City,the basic situation of water resources in Shiyan City and its districts and counties was explored.Then the pressure-state-response evaluation system of water ecological security in Shiyan City was constructed from the perspective of social economy.Finally,based on the evaluation results of water resources quantity and water ecological security in Shiyan City,the relationship between them was analyzed,and the current situation and main limiting factors of water ecological security in Shiyan City and its districts and counties were comprehensively analyzed,and corresponding control measures were proposed.The following contents are obtained:(1)The water production depth in Shiyan City has shown a decreasing trend,from618.63mm in 1980 to 423.62mm in 2018,and the corresponding water production has dropped from 14.646 billion m~3to 10.035 billion m~3.In terms of the spatial pattern of water production,high-value areas have been concentrated in the southwest of Shiyan City;low-value areas have been concentrated in the southeast and north-central areas.From the perspective of the driving factors of water production,the contribution rates of precipitation,potential evapotranspiration,and land use change to water production changes were 77.08%,22.79%,and 0.13%,respectively.From the perspective of water production depth of each category,construction land is 690.87mm,grassland is645.43mm,unused land is 628.06mm,cultivated land is 610.78mm,forest land is497.41mm,and water area is 471.33mm.From the perspective of the water production of administrative divisions,the water production of all districts and counties decreased to varying degrees during the study period.The average water production depth of each district and county was 608.262mm in Zhuxi,543.632mm in Maojian,533.86mm in Zhushan,510.474mm in Yunyang,509.142mm in Zhangwan,501.328mm in Danjiangkou,496.542mm in Fangxian,486.56mm in Yunxi.(2)The water conservation in Shiyan City has shown a downward trend,from7.635 billion m~3in 1980 to 3.276 billion m~3in 2018.There are significant differences in water conservation among various types.The average water conservation depths of woodland,grassland and arable land are respectively 286.39mm,258.07mm and92.35mm.The rest of the land types have a small amount of water conservation during part of the study period.The total amount of water conservation in the districts and counties of Shiyan City at the time of the study was 6.386 billion m~3in Fangxian,5.174billion m~3in Zhuxi,4.808 billion m~3in Zhushan,4.733 billion m~3in Yunyang,4.173billion m~3in Yunxi,3.481 billion m~3in Danjiangkou,0.758 million m~3in Maojian and0.729 million m~3in Zhangwan.All districts and counties showed a decreasing trend.(3)The overall change in the amount of available water resources in Shiyan City was relatively small,from 4.908 billion m~3in 1980 to 4.731 billion m~3in 2018.In 2010and 2018,the available water resources per capita are 1369.07 m~3and 1389.11 m~3.The annual available water resources in each district and county are 97.3 million m~3in Maojian,113 million m~3in Zhangwan,686 million m~3in Yunyang,680 million m~3in Zhuxi,645 million m~3in Danjiangkou,613 million m~3in Yunxi,748 million m~3in Zhushan and Fangxian is 887 million m~3.In 2010 and 2018,the water supply and consumption ratio of Shiyan City was 10.12 and 11.84,respectively.Among the districts and counties,the water supply and consumption ratios are greater than 10 in Zhuxi,Zhushan,Fangxian,and Yunxi,between 5-10 in Danjiangkou and Yunyang,and less than 5 in Zhangwan and Maojian.(4)The water ecological security of Shiyan City is generally at a poor level,and there is a trend of continued deterioration.The water ecological security indexes from2008 to 2019 were 0.63,0.60,0.56,0.44,0.34,0.36,0.40,0.31,0.32,0.46,0.30,0.29.The water ecological pressure index has dropped significantly;the status and response index has changed little,which has a limited positive effect on the ecological safety index of Shiyan City.The amount of water resources has always been the main obstacle factor for water ecological safety in Shiyan City.The main obstacle factor for water ecological safety has also been transformed from pollution indicators(proportion of investment in wastewater treatment,total sewage discharge,and number of wastewater treatment facilities)into socio-economic indicators(Permanent population,urbanization rate).The changes in the water ecological safety index and pressure index of each district and county are roughly the same as those of Shiyan City,and the changes in the status and response subsystems are relatively small.The natural endowment conditions of water resources,urbanization indicators and water pollution control are the main factors restricting the water ecological security of all districts and counties.(5)The spatial differentiation of the current situation of water ecological security in Shiyan City is specifically manifested in the following three categories:the first category is rich in water resources and a higher water ecological security index,such as Zhuxi and Fangxian;the second category is rich in water Resources and low water ecological safety indexes,such as Yunyang,Yunxi,and Zhushan,should adhere to sustainable development and increase investment in water environment governance;the third category is poor water resources and high water ecological index,such as Zhangwan,Maojian,and Danjiangkou.The efficiency of water resource utilization should be improved,the ways of transforming green water into blue water should be broadened,and hospitable water and rainwater should be fully utilized.