| Wetland ecosystems have provided essential ecological services for human survival and development,and in particular have significant climate regulation functions.However,rapid urbanization has led to degradation and loss of wetland resources and increased landscape fragmentation.In recent years,studies on the climate regulation function of wetlands have mainly focused on isolated wetland units,ignoring the overall function of wetland networks.This study takes the mitigation of urban heat island effect as the research perspective,explores the construction method of wetland ecological network,and explores the key nodes and elements affecting the function of wetland network,so as to provide scientific basis for urban wetland conservation and restoration.This study takes urban wetlands in Changchun as the research object,quantifies the cooling effect of urban wetlands using the spatial analysis method of GIS,and reveals the influence mechanism of wetland spatial morphology and surrounding landscape features on the cooling effect.Based on the improved method of the source selection and resistance assessment system,we construct a wetland ecological network with heat island effect mitigation as the main feature.The ecological network is optimized by overlaying the source edge increasing strategy and the stepping stone edge increasing strategy,and the optimization results of the ecological network are evaluated by combining complex network theory and background wind analysis,so as to formulate the construction and maintenance strategies of the ecological network.The main results of this study are as follows.(1)The surface temperature distribution in Changchun city decreases radially from the central part of the city to the surrounding area,and the strong heat island area shows a significant aggregation effect.The average cooling extent of the urban wetlands was 300 m.The temperature of the area close to the wetlands was reduced by about 4.91°C.The cooling of the wetlands tended to increase logarithmically with the area,and the efficiency threshold was1.02 hm2.The cooling intensity and cooling extent of the wetlands in the urban area were greater than that of the green areas,and the average cooling intensity was 3.35°C higher than that of the rural wetlands.Correlation analysis showed that the size of the wetland,the area of surrounding buildings,and hydrological connectivity were all significantly and positively correlated with the cooling effect,and that the green space surrounding the wetland did not enhance the cooling intensity of the wetland,but allowed it to maintain its cooling effect over a larger area.(2)The ecological core area of Changchun City accounts for 70.66% of the total wetland area.There are few large wetlands in the study area,the distribution of wetlands is relatively scattered,and the fragmentation of wetland landscape is serious.The wetland cooling capacity has significant spatial heterogeneity(low in urban and high in rural area),with an average of 3.94 k and a maximum of 6.42 k.A total of 24 ecological source sites were extracted by combining the wetland cooling index.The results of the resistance surface show a significant correlation between resistance values and surface temperature,and there are differences in resistance values between different landscape elements and the same landscape.The initially constructed ecological network includes 23 key ecological corridors and 47 potential ecological corridors,the spatial distribution of which overlap highly.Combined with the distribution of ecological corridors,48 stepping stone patches located inside the corridors were extracted;24ecological pinch points requiring improvement and protection were identified based on circuit theory,which are highly consistent with the distribution of rivers in urban areas.(3)The initially constructed ecological network is a fully connected network,but the degree distribution and betweenness distribution of nodes in the network are not uniform,and there are fewer nodes with high connectivity.The node degree distribution and betweenness distribution of the optimized network are more uniform,and the node connectivity is significantly improved by overlaying the source edge increasing strategy and the stepping stone edge increasing strategy to optimize the wetland ecological network.The optimized ecological network is more resistant to shocks with a node failure ratio threshold of 25%.The optimized network connectivity robustness is significantly enhanced in both random and deliberate attack scenarios;the network connectivity robustness can still be maintained at 0.3 under the simulated policy-protected ecological sources scenario,where all stepping stones are destroyed.The main ventilation corridors that need to be built and maintained within the ecological network account for 30% of the total corridors,and the actual situation in Changchun is such that a corridor width of about 30 m is appropriate.Urban wetlands have a significant cooling effect in summer.Wetland area,hydrological connectivity and surrounding buildings have a significant impact on the cooling effect,therefore,wetland planning and optimization in densely built-up areas can improve the cooling effect.Based on the improved ecological network construction method,this study constructs and optimizes an ecological network with the ability to mitigate the heat island effect,and each element within the network plays a different role in mitigating the heat island effect.The optimized network space structure is more stable and has a better ability to maintain network robustness.The improved method effectively improves the scientific and implementability of the wetland network to mitigate the heat island effect,and can also provide a reference for the development of heat island threat reduction strategies and wetland ecological conservation planning in other regions facing contradictions between rapid development and wetland conservation construction. |
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