Urban Ecosystems

, Volume 15, Issue 4, pp 809–848 | Cite as

Understanding the metabolism of urban-rural ecosystems

A multi-sectoral systems analysis
  • R. Villarroel WalkerEmail author
  • M. B. Beck


A Multi-sectoral Systems Analysis (MSA) methodology is presented as a tool for identifying the level of importance of flows of energy and materials (water, nitrogen, phosphorus, and carbon) as they pass through an anthropogenically manipulated system. That system comprises a web of processes, across a total of five industrial sectors: water, forestry, food, energy and waste management. Given the heterogeneous nature and quality of data sources, the propagation of data uncertainty is considered through a Regionalized Sensitivity Analysis (RSA) procedure, based on the Monte Carlo simulation approach. The MSA reveals the advantages of studying different material cycles simultaneously, in addition to interpreting them individually, while gaining insight into the magnitude of the associated flows. The proposed framework is illustrated for a case study of the Upper Chattahoochee Watershed, in which parts of Metro Atlanta are located. Results show that natural flows are predominant in the water and energy cycles. Direct human manipulations of water, i.e., withdrawals for public supply and power generation, are less than 25% of the amount received as precipitation. Solar input is 200 times the total demand for electricity. Apart from sun-light, gasoline for transportation is the flow with the largest content of energy; it is responsible for providing 71% of the total demand of fuels for uses other than power generation. In contrast, cycles of nutrients such as N and C are strongly related to the flows of fuels, mainly coal and natural gas. In a second tier, fertilizer use and the poultry industry in the region are significant for the use of nitrogen. Phosphorus fluxes are similarly dominated by the food sector and, as a consequence, to a lesser extent by the water sector, because of water’s role as a waste-conveyance medium.


Substance flow analysis Phosphorus Resources Waste management Energy  Nitrogen Carbon Urban metabolism 



The work on which this paper is based is part of an international, inter-disciplinary network of research—the CFG Network ( CFG was begun in 2006, enabled through the appointment at that time of MBB as an Institute Scholar at the International Institute for Applied Systems Analysis (IIASA), Laxenburg, Austria. We readily acknowledge this stimulus to our work. Throughout, CFG has been funded by the Wheatley-Georgia Research Alliance endowed Chair in Water Quality and Environmental Systems at the University of Georgia, in particular, in support of a Graduate Assistantship and now Postdoctoral Fellowship for RVW. The freedom of enquiry enabled through this form of financial support has simply been invaluable. The authors would also like to thank the two anonymous reviewers for their thorough and insightful comments.


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© Springer Science+Business Media, LLC 2012

Authors and Affiliations

  1. 1.Warnell School of Forestry and Natural ResourcesUniversity of GeorgiaAthensUSA

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