Study On Comprehensive Ecological Risk Assessment And Its Prevention And Control Of Urban Expansion In Hohhot

Rapid urbanization,while promoting the rapid development of society and economy,is also changing the natural base of cities.It is intuitively expressed as a large-scale expansion of urban land.Urban expansion is bound to encroach on cultivated land,grassland and other ecological land,destroy the structure and function of the ecosystem,and cause a variety of ecological and environmental problems.Environment is the foundation of urban development.A good ecological environment is the foundation of urban development.Blind urban expansion at the cost of ecological damage is not conducive to sustainable urban development.In recent years,how to balance the relationship between urban development and ecological protection has become a research hotspot in the fields of ecology,urban geography,regional development,and urban planning.Taking the urban area of Hohhot as the research area,this paper carried out a comprehensive ecological risk assessment and prevention and control research of Hohhot’s urban expansion in 1990,2001,2010,and 2017.Based on the urban land expansion in Hohhot,this paper constructs a comprehensive ecological risk assessment model of"factor-exposure-impact-response".Using principal component analysis,gray correlation,circle analysis,and bivariate spatial autocorrelation to analyze the spatio-temporal evolution characteristics of ecological risks and the spatiotemporal response mechanism to urban expansion.Aiming at the fact that the ecological risk in the study area is increasing year by year,constructed an ecological security pattern based on the minimum cumulative resistance surface model.Study on the prevention and control of ecological risks in various towns in Hohhot,and propose ecological protection countermeasures.The main conclusions are as follows:(1)The analysis results of the spatial and temporal characteristics of urban land expansion in Hohhot show that:Firstly,the area of built-up area of Hohhot increased from 73km~2 to 260km~2 from 1990 to 2017.The rate and intensity of urban expansion are increasing.Secondly,The peak value of the expansion intensity of construction land was concentrated in the peripheral area of the built-up area,and it in the center of the built-up area and the urban fringe area was low.Thirdly,the main directions of urban expansion were east,southeast,and southwest.Fourthly,the expansion of construction land leads to changes in the structure of land use,which is manifested by a sharp decrease in the area of cultivated land,unused land and grassland.Finally,the proportion of construction land area in each township showed an upward trend during the study period.And construction land expansion intensity varies greatly and the characteristics of periodic changes were obvious.(2)The results of comprehensive ecological risk assessment in Hohhot show that:Firstly,from 1990 to 2017,the comprehensive ecological risk value of Hohhot increased from 0.395 to 0.467.The growth rate of value-at-risk has continued to rise,and the risk level has evolved from low to medium.In each target layer,the risk value of the factor layer,the exposure layer,and the influence layer showed an upward trend,and the risk value of the response layer showed a downward trend.Secondly,the ecological risk grade area of the study area was distributed in a circle,which the ecological risk value from the city center to the periphery is getting lower and lower.Thirdly,the ecological risk value of each township was on the rise,and the risk levels were from low to high.(3)The research on the spatial and temporal response of ecological risk to urban expansion in Hohhot shows that:Firstly,from 1990 to 2017,the gray correlation index of the expansion intensity of construction land and the comprehensive ecological risk value was 0.83,which indicates that there was a strong temporal correlation between the two.Secondly,There was a strong spatial correlation between urban land expansion and ecological risks in Hohhot,as shown in:there was a clear circle-to-layer relationship between the comprehensive ecological risk value and the expansion intensity of construction land.They appeared as high-value agglomerations in built-up areas(buffers 1-8),and low-value agglomerations in urban fringe areas(buffers 20-24).The expansion direction of construction land was consistent with the expansion direction of high ecological risk grade areas.(4)The results of ecological risk prevention and control research based on the ecological security pattern show that:Firstly,a total of 365.6km~2urban extension source and 424km~2 ecological protection source were identified,and 15 ecological corridors(346km)and 11 ecological strategic points were extracted in the study area.Secondly,partition the study area into ecological security zones.Ecosystem conservation and optimizing buffer suitable for expansion of ecological land.Ecotone and ecological protection suitable for urban land expansion.Thirdly,coupling ecological strategic points,ecological corridors,ecological sources and ecological security zones to form an ecological security pattern of“one ring,two belts,three corridors,three areas,and multiple centers”.(5)The results of the study on the prevention and control of ecological risks by zone show that:Firstly,the optimized development zones of Hohhot are the streets of Huimin District,Yuquan District and Saihan District.The key development zones are Xincheng Street,Xiaoheihe Town and Jinhe Town.Restricted development zones are Youyouban Town,Huanghesha Town,and Yulin Town.Banned development zone for Baohe Shaozhen.Secondly,based on the ecological security pattern,put forward suggestions for the prevention and control of ecological risks for each township.