| Steel resource outsourcing is an important means to allocate resources efficiently and reduce the impact of local ecological environment in the process of urban development,but the resource trade caused by outsourcing also brings the transregional environmental impact.Understanding the metabolic process of urban resources and evaluating the impact brought by outsourcing play an important role in decision-making support for rational management of resources and coordinating the sustainable development of urban areas.This study took steel metabolism in Shanghai's five types of infrastructure as the main research object,estimating the temporal and spatial evolution law of steel stock and flow from 1920 to 2019 by using the method of material flow analysis and GIS.On this basis,we evaluated the environmental impact caused by steel metabolism and cross-scale outsourcing in combination with the development of steel industry and the investigation of cross regional trade.Finally,we also put forward some relevant policy suggestions.The main conclusions are as follows:(1)In the past 100 years,the overall steel stock in Shanghai's infrastructure has shown a steady upward trend,with a total increase of nearly 700 times.In 2019,the cumulative stock reached 382 million tons.Among them,the contribution of residential and non-residential infrastructure was as high as 68-99%,while the transportation system contributed less(1-32%).On the one hand,the increasing demand for residential and non-residential buildings due to social and economic development has stimulated the rapid expansion of the real estate market,which also caused the sustained and rapid increase of the cumulative stock in buildings;On the other hand,the proportion of steel in materials was rising owing to the transformation of building structure.Spatially,the distribution of steel stock showed a pattern of expansion from the central urban area to the suburbs and outer suburbs.(2)In the past 100 years,the inflow of steel materials into infrastructure in Shanghai increased firstly and then declined.Before 2010,especially from 1990 to 2010,the average annual growth rate of steel input was as high as 10.8%.Later,it showed a negative growth of 4.9%per year affected by a series of regulatory policies for the real estate market.In the composition of inflow,more than 93%was concentrated in residential and non-residential buildings.Significantly,steel investment in non-residential buildings exceeded that in residential buildings in 2019,becoming the infrastructure type with the largest contribution since the continuous improvement of residents' consumption level and demand.The inflow of steel in the transportation system is affected by the implementation of transportation construction projects in different periods,and the overall change fluctuates little.In terms of spatial distribution,similar to the pattern of steel stock,steel input also showed a trend of diffusion from the city center to the outer suburbs.(3)We found that Shanghai's iron and steel industry had experienced the development process from self-production to industrial outsourcing according to the summary of urban construction industry associations,major iron and steel enterprises and literature.Before the 1970s,the city's steel consumption basically depended on local production.After that,the product positioning of Shanghai's steel industry gradually shifted to high-end industrial steel,while construction steel mainly depended on outsourcing.Spatially,these steel materials mainly came from some cities with large steel production bases,and the distribution area presented a diffusion trend of from coastal to inland,from surrounding to remote".Among them,Jiangsu Province was the main source of steel for construction in Shanghai.From the upstream supply chain of iron and steel materials,China's iron ore mainly depended on international imports.Australia has always been the main supplier of iron ore in China,followed by Brazil,South Africa,India and other places.(4)The transregional environmental impact of steel metabolism in Shanghai's infrastructure is mainly concentrated in East China dominated by Jiangsu.In terms of impact categories,steel production has the greatest impact on the ecosystem health(65.6%),followed by resource consumption(18.6%)and human health(15.8%).We also found that the impact of steel outsourcing on marine ecotoxicity is the highest(33.9%),followed by freshwater ecotoxicity(20%)and metal depletion(17.4%)through the further analysis of the environmental impact.From the perspective of the transnational iron ore trade,it has the greatest impact on metal depletion,accounting for more than 80%of all exporting countries,of which Australia has always borne the most environmental impact.In addition,the mining process of iron ore also has a great impact on ecological toxicity,human toxicity and particle formation.(5)In view of the environmental impact caused by steel metabolism and resource outsourcing of Shanghai's infrastructure,we put forward some policy suggestions.Firstly,we need to improve the service life of buildings use new materials to alleviate the demand for primary steel resources.Secondly,we should strengthen the recovery of scrap.In addition,it is important to optimize the scrap smelting process and refining technology,and establish a complete scrap recycling system and management mode.we can improve the utilization efficiency of local resources and reduce the cross regional ecological environment impact caused by resource outsourcing through aforementioned. |
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