| Urban wetland refers to wetland under significant influence from human activities,which is located in the urban center or edge zone and formed due to natural or artificial reasons.As the composition of urban complex ecosystems,it covers various types such as river,lake,reservoir,marsh,coast,paddy field,and culture pond.Providing multiple important ecosystem services for people's production and life,urban wetland cannot be replaced by other urban natural ecosystems.However,wetland is one of the geographical units that disappear the most rapidly in the urbanization process,and urban wetland is faced with huge ecological threat owing to rapid urbanization.Under this background,the composition,structure and functions of urban wetland ecosystem are discussed.A scientific theoretical research framework is established,and it has already become an important content in the research field of urban wetland protection and utilization to study relevant issues about its ecological service values.Under the guidance of well-being geography,welfare economics,relevant theories of ecology,and sustainable development theory,relevant concepts and connotations of urban wetland ecosystem are discussed in this paper.Meanwhile,the structure,functions and major ecological processes of urban wetland ecosystem are illustrated.Besides,a systematic discussion is made on the driving and feedback mechanism between urbanization and changes of urban wetland ecosystem structure and functions.In addition,an overall theoretical framework about the interaction between urbanization and urban wetland ecosystem is established.According to the study,under the drive of urbanization,factors like changes of urban land utilization,gathering of industry and population,and corresponding human disturbance enhancement have formed the driving mechanism of urban wetland ecosystem changes.Under such influence,the material composition of urban wetland changes,and the biological process,hydrologic process and biogeochemical process alter accordingly,triggering the change of its ecosystem services.Such change is also fed back to urban ecosystem through the service supply of urban wetland and other ecosystems,which will further influence urban ecology.Urban wetland ecosystem service is the sum of various material and non-material earnings gained by humans from urban wetland ecosystem,and the comprehensive reflection of urban wetland ecosystem values based on the perspective of human development.Generally speaking,it includes four service types which are supply service,regulation service,support service and cultural service.Specifically speaking,it covers ten items which are material production,water supply,flood water storage,atmosphere regulation,local climate regulation,pollutant disposal,soil conservation,material cycling,biological diversity maintenance,and various cultural services.Based on this,by a case study of Jiangbei New District in Nanjing,the evaluation of wetland ecosystem service values is studied systematically,and an analysis is made on the trade-offs and synergies of urban wetland ecosystem services through the time variation of service values.According to the study,the method of decision tree classification model can be utilized to realize the extracting target of water wetlands in the research area.Through explaining Landsat TM/ETM/OLI remote sensing images of 2002,2009 and 2015,data of wetland land utilization/land coverage changes in Jiangbei New District are acquired.Via spatial-temporal change analysis on the wetland area and landscape fragmentation analysis of the wetland,it is discovered that lake wetlands in Jiangbei New District are mainly distributed in the north of Liuhe,water wetlands are mainly distributed in regions along Chuhe River and Macha River,and pond wetlands show relatively concentrated distribution in regions along rivers in the east,south,north and southwest of Jiangbei New District as well as areas along Chuhe River and its branches,presenting a spatial pattern of“dispersion in the whole region but concentration in small areas”.Especially since 2009,the areas of river and pond wetlands in the research area have been reduced rapidly,and the spatial dispersion degree has also become higher and higher.The rapid urbanization process is a major reason causing wetland area reduction and landscape fragmentation in the research area,and pond wetland and river wetland will be disturbed by human activities more easily.The economic values of ecosystem service value equivalent and standard equivalent are modified by introducing space-time adjustment factor and production value of farmland per unit area.Meanwhile,an urban wetland ecosystem service value evaluation system is established,and empirical analysis is conducted by a case study of Jiangbei New District.According to the study,the wetland ecosystem service values of Jiangbei New District in 2002,2009 and 2015 are 6060.77×10~6 Yuan,9244.62×10~6Yuan and 6880.95×10~6 Yuan respectively,so the time frame variation coefficient of service value is relatively high,showing a fluctuation trend of“rapid increase first and then rapid decrease”.Regulation service is the core structure of wetland ecosystem service value in Jiangbei New District,and the service value of flood diversion and storage is the highest.However,the value of supply service is the lowest,as paddy field production has affected water supply in the area.After 2009,the descent velocity of wetland ecosystem service value in Liuhe is relatively slow,and the proportion in total value of the area increases year by year.The wetland ecosystem service value in Pukou presents the highest variation coefficient and the lowest wetland ecosystem stability.Based on the evaluation data of wetland ecosystem service values in Jiangbei New District,by utilizing the ecosystem service variability index and ecosystem service index,spatial analysis is conducted for the spatial variation features of ecosystem service values from 2009 to 2015 in the research area via space mapping method.The following spatial features of wetland ecosystem service value changes in Jiangbei New District are discovered.Firstly,the space of slight gain is relatively huge,and the significant gain regions mainly center on the north of Liuhe.Secondly,significant loss regions of service values are mainly located in surrounding areas of cities and towns,presenting T-shape distribution along the drainage basin of Chuhe River.Thirdly,ecological degradation happens to key wetlands like Lvshuiwan due to unsuitable utilization.According to the contrastive analysis,wetland ecosystem service items and service categories in the research area mainly keep a synergic relationship.However,local tradeoff exists between flood diversion and storage service and soil conservation service,and local tradeoff is also presented between support service and other service types.Land utilization/land coverage changes caused by human activities are the major reason of resulting in urban wetland ecosystem trade-offs.In the future,the ecological function of urban wetland should be valued in planning and construction of Jiangbei New District,and key wetland resources in riverside areas must be conserved and restored.Besides,attention should be paid to the flood diversion and storage value of urban wetland,and a“sponge city”needs to be planned and constructed in Jiangbei.Meanwhile,protection and conservation for wetland resources in regions along rivers in Pukou as well as areas along Chuhe River should be strengthened.Moreover,great importance must be attached to conservation for lake wetlands in the north of Liuhe as well as wetlands in areas along Chuhe River in the middle and south.Finally,the current situation of wetland fragmentation near Chuhe River and its major branches should be improved,to increase the ecological environment quality. |
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