Research on urban metabolism is a complex decision-making process having a direct impact on human health and the environment both locally and globally. The paradigm of urban metabolism has been formulated in an attempt to focus thinking towards a balanced co-evolution of the economic, physical and social environments while living within the carrying limits of the supporting ecosystems. Analyzing the structure and functioning of the urban metabolic system revealed ways to optimize its structure by adjusting the relationships among compartments, thereby demonstrating how ecological network analysis can be used in urban system research. A fresh perspective focuses on the traditional exergy-based accounting linking the analysis of exergy utilization in the sector of urban socio-economic system. Exergy provides a unified measure of various forms of materials and energy carriers, and thus qualified as a basic medium used in the bookkeeping to qualify ecological networks of exchange. The application of Extended Exergy Accounting (EEA) determines cumulative exergy consumption associated with not only raw material inputs but also labor and capital inputs and non-energetic externalities. Money can also provide a common currency by using economic valuation methods to capture the contribution of ecosystems. The proposed thermodynamic approach is not meant to replace, but to complement an economic approach.
Our objectives in this study were threefold. First, based upon the division of urban society sectors and accounting of EEA flux, we wanted to construct an urban metabolism network models without regard to the bank system and government. This model is divided into seven sub-systems, including: (1) Extraction (Ex), including mining and quarrying, oil refining and processing, and the inflow of energy carriers from the external environment; (2) Conversion (Co), comprising heat and power plants; (3) Agriculture (Ag), including harvest, forestry, fishery, and food processing; (4) Industry (In), manufacturing industry except food industry and oil refineries; (5) Transportation services (Tr); (6) Tertiary sector (Te), including construction and other services; (7) Domestic sector (Do), households. The domestic sector has changed from a final consumption to an important labor exergy inflow transferring to other sectors. Second, use of EEA data of original works listed in the references enables to finish an urban ecosystem network analysis in the case study of Dalian. Finally, the assessment results of Dalian in order to gain insights into the economic processes oriented to sustainable urban development. It may present an initial diagnosis of resource utilization efficiency, input/output structure and environmental impact on urban scale and priority on funding of the whole sectors.
The results show that the indicates that Dalian, as a city with a "large and complete" structure, depends on the larger external systems surrounding the city which can supply resources and services that are lacking within the city. The thermodynamic efficiencies of individual sector in Dalian performed in a good level. The social system in Dalian was a highly competitive network, and there were eight competitive relations and only two mutualistic ones. The Do-and Ag-sector were the major contr olling factors of the system. Do-and In-sector have the larger environmental burden. Such a knowledge is a necessary prerequisite to perform a reliable cost-benefit evaluation of urban sustainability strategies. It will be necessary to strengthen the urban metabolic functions described in our model in such a way that the impact on the environment can be significantly reduced, thereafter providing more specific guidance on how to develop ecologically sustainable cities.