Impact Of Urban Expansion On Ecosystem Services In The Context Of Co-city Development In Wuhan Metropolitan Area

Ecosystem services are the natural environmental conditions and utilities that maintain human survival.They serve as a link between the natural ecological environment and economic and social systems.With the acceleration of urbanization,regional ecosystems are constantly disturbed,showing dramatic and complex spatial and temporal changes,leading to various ecological and environmental problems,which have a wide and farreaching impact on ecosystem services,such as over-exploitation of water resources,water pollution,habitat fragmentation,land desertification and soil conservation.The Wuhan city circle is the seventh metropolitan planning area approved by the state.It is one of the most promising regional economic associations after the Yangtze River Delta,the Pearl River Delta and the Beijing-Tianjin-Hebei region.It is the core area of population convergence,economic development and industrial agglomeration in Hubei Province.Under the background of the current urban integration development,there are many problems in Wuhan city circle,such as significant differences in ecosystem services,increasing regional ecological contradictions and unclear urban planning concepts.In view of this,based on the In VEST(Integrated Valuation of Ecosystem Services and Trade-offs)model,this study quantitatively evaluated seven ecosystem service functions of food production,water production,habitat quality,soil conservation,water purification,carbon storage and recreation potential in Wuhan metropolitan area from 2000 to 2020.The spatial autocorrelation analysis and hotspot analysis were used to identify the aggregation degree of each service function and reveal the spatial and temporal dynamic characteristics of ecosystem services in the study area.Based on the ’ Exclusion-Inclusion’ framework method,the distribution map of urban construction land in the study area was extracted.Using the idea of ’ hierarchical aggregation ’,five major urban belts extending outward with Wuhan as the center were constructed.The evolution of urban expansion in the direction of each urban belt in the past 20 years was analyzed,and the characteristics of regional urban expansion under the background of urban integration in the study area were clarified.Through the geo-information map,the spatial and temporal evolution of ecosystem services in the scope of urban construction land under the background of urban integration development was studied,and the impact of urban construction land expansion on ecosystem services was analyzed.Pearson correlation coefficient is used to analyze the correlation between urban expansion and ecosystem services,and the ecosystem service functions with high correlation are selected.K-means clustering method is used to divide the ecosystem service functional areas.From the perspective of bridging and coordination among member cities,differentiated ecosystem management and control suggestions are proposed.The research can provide scientific basis for the effective management of ecosystem services,the sustainable development of ecosystems and the construction of ecological civilization,and provide reference for land space planning and natural resource management.The results show:(1)Among the ecosystem service functions in the study area,the recreational potential,water yield and grain production function showed an upward trend,while the water purification capacity showed a downward trend.The habitat quality and soil conservation function maintained a dynamic balance,and the overall change of carbon storage was small.The global spatial autocorrelation of the four services showed a significant positive correlation.The multi-year Moran ’s I index of water purification and soil conservation functions was low,while the Moran ’s I index of carbon storage,habitat quality and water yield remained high throughout the year.The area of the study area that can provide four or more high-value ecosystem services accounts for 10.02 %,and 89.98 % of the area can only provide three or less high-value ecosystem services.(2)In the past 20 years,the area of urban construction land in the study area has increased significantly.Through the ’ center outward expansion,local inward expansion ’and the establishment of urban nodes,the distribution system of urban construction land with multi-line,multi-point,mesh infiltration and regional network has been constructed.In 2020,the area of urban construction land will reach 5242.16 km2,which is 339.37 %higher than that in 2000.The matching rate between the results and the field survey points is 92.84 %,and the overall consistency with the existing product data is 81.56 %.From2000 to 2005,the degree of urban expansion in the study area increased significantly,and the proportion of urban zones increased by more than 50 %.From 2005 to 2015,the degree of urban expansion tended to be balanced,with an increase rate of 30 %-70 % every 5years.From 2015 to 2020,the degree of urban expansion increased slowly,and the increase rate was generally below 27 %.The identification of the commuting range of regional central cities shows that the commuting range of Wuhan in 2020 has expanded by 1109.73km2 compared with 2015,up 136.45 % year-on-year,and has formed a large-scale commuting area covering many surrounding counties and cities with Wuhan as the center.(3)The recreational potential function within the scope of urban construction land is higher than the average level of the study area,while the other six services are lower than the average level.The changes of ecosystem services in the commuting area are consistent with those in the urban construction land,and the water yield,habitat quality and water purification function are generally higher than those in the urban construction land.There was a high positive correlation between urban expansion and recreation potential,phosphorus content and water yield function in the study area,with an average correlation coefficient of 0.91,0.88 and 0.89,respectively.There was a high negative correlation with soil conservation capacity,with an average correlation coefficient of-0.85.Habitat quality and carbon storage function have different response mechanisms to urban expansion with regional changes.The correlation between nitrogen content and food supply function and urban expansion is not high.The annual average values of six ecosystem service functions with high correlation with urban expansion were analyzed by cluster analysis.The results showed that the study area was divided into four functional areas : ecological protection area,ecological transition area,urban living area and production and living area.The ecological protection zone is dominated by maintaining vegetation coverage,preventing soil erosion and increasing water yield.The ecological transition zone is dominated by enhancing landscape connectivity and increasing buffer zones;the urban living area is dominated by increasing the number of urban green space and enhancing the complexity of vegetation structure.The production and living areas are dominated by optimizing the spatial structure of cultivated land and controlling the red line of cultivated land.