| A city is a complex and diverse system.With the development of regional socioeconomic and cultural,urban space and expanding the scope,increasing industrialization process,various contradictions and the consequent pressure between urbanization and the environment have become increasingly prominent.Since the United Nations held the first conference on human and environment in Stockholm in 1972,human efforts to protect and improve the environment have never stopped.Since the beginning of reform and opening up in 1978,China has achieved long-term and sustained high-speed and ultra-high economic growth and achieved large-scale urbanization.In the process of high-speed urbanization,many challenges such as the depletion of natural resources and the degradation of ecological environment are the biggest problems we are facing.Just as life is a metabolic phenomenon,it is the exchange process of energy,matter and the environment,so cities are also maintained by the exchange of matter and energy with the outside world.Since Eurostat released the first EW-MFA framework based on the socio-economic system in 2001,material flow analysis in the field of material metabolism has developed rapidly.Based on the EU's EW-MFA framework and Cui Xuezhu's Urban Metabolism(UM)model,this research constructs an Urban Metabolite Material Flow Analysis(UM-MFA)model.The UM-MFA model systematically analyzes the material flow after the initial unfolding of the material flow in the urban metabolic system by introducing the concept of material circulation and balanced metabolism,and using modules as the basic unit of the model.After improving a set of extensible and comparable urban metabolic material flow analysis framework and methods,the material flow account was constructed,and the corresponding material flow conversion coefficient was established,which provided method and tool support for the construction of standardized Urban Metabolic framework.The framework provides method and tool support.The urban metabolite flow model constructed in this study includes five modules: agricultural activities,industrial activities,daily life activities,construction activities,and transportation activities,involving intraregional extraction(IRE),intraregional output(IRO),import and export(Imp and Exp),regional discharge(IRD),circulation(Cir),balance item(BI)and net stock(NS)seven basic items.Based on the principle of conservation of mass,the UM-MFA balance equation of urban metabolism is established.Taking Lanzhou as a specific case,using the established UM-MFA model to study the material flow in Lanzhou.The material flow panorama of Lanzhou in 2009 and 2018 and the time series of material metabolism in Lanzhou from 2009 to 2018 were showed.Then,the change trend of urban resource load in Lanzhou from 2009 to 2018 is analyzed.On the basis of material flow analysis,based on the national level evaluation indicators provided by the EW-MFA Guidance Manual issued by Eurostat in 2015,a city-level material flow evaluation index system was established to analyze and evaluate the material flow characteristics of Lanzhou.The characteristics of urban resource load in Lanzhou from 2009 to 2018 are given.The main conclusions of this article are as follows:(1)The current status of material metabolism in Lanzhou City shows that the total material flow intensity in Lanzhou City was relatively high,and the material productivity of urban metabolic agricultural activities continued to increase from 2009 to 2018.As the use of consumable material resources such as chemical fertilizers and agricultural films increases,the pressure load on the environment has also increased;while the material production of urban metabolic industrial activities has increased,energy consumption and regional emissions have decreased by a certain amount.Government energy-saving and emission-reduction measures have been effective obviously.With the advancement of urbanization,both the import and stock material flow of urban metabolic activities of daily life are on the rise,while the overall material flow is on the decline;the material quality of infrastructure investment is huge,especially the road construction is greatly improved,and housing construction is basically maintained in a relatively stable range;the number of taxis and buses for transportation activities has steadily increased.With the implementation of the government's energy-saving and emission reduction policies,the amount of pollutants discharged in transportation activities has not increased much.The results of the study on material metabolism in Lanzhou indicate that the trend,extent and intensity of material metabolism in the city are greatly affected by government actions.(2)The analysis of the characteristics of the flow of metabolites in the cities of Lanzhou City shows that the current economic growth of Lanzhou City has gradually changed from extensive to intensive.From an overall point of view,the direct material input of urban metabolism in Lanzhou City was relatively decoupled from economic growth.Urban metabolism in Lanzhou City is affected by the quality of the extracted substances in the region.The implementation of energy saving and emission reduction policies was the driving force for the continuous improvement of urban production capacity and the reduction of pollutant emissions year by year.(3)From 2009 to 2018,the environmental pressure caused by urban metabolism in Lanzhou City has gradually changed from the direct emission of substances in the region to the potential environmental pressure mainly due to the increase in the net stock of substances in the region.Therefore,while strengthening energy conservation,emission reduction and infrastructure construction,the government should pay enough attention to the potential environmental pressures based on the net inventory of construction activities,and introduce relevant recycling policies to maximize the recyclability of materials and to prevent potential environmental pollution caused by the increase in net inventory. |
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