title: A Network Flow Analysis of the Nitrogen Metabolism in Beijing, China.
abstract: Rapid urbanization results in high nitrogen flows and subsequent environmental consequences. In this study, we identified the main metabolic components (nitrogen inputs, flows, and outputs) and used ecological network analysis to track the direct and integral (direct + indirect) metabolic flows of nitrogen in Beijing, China, from 1996 to 2012 and to quantify the structure of Beijing's nitrogen metabolic processes. We found that Beijing's input of new reactive nitrogen (Q, which represents nitrogen obtained from the atmosphere or nitrogen-containing materials used in production and consumption to support human activities) increased from 431 Gg in 1996 to 507 Gg in 2012. Flows to the industry, atmosphere, and household, and components of the system were clearly largest, with total integrated inputs plus outputs from these nodes accounting for 31, 29, and 15%, respectively, of the total integral flows for all paths. The flows through the sewage treatment and transportation components showed marked growth, with total integrated inputs plus outputs increasing to 3.7 and 5.2 times their 1996 values, respectively. Our results can help policymakers to locate the key nodes and pathways in an urban nitrogen metabolic system so they can monitor and manage these components of the system.
authors.affiliation: State Key Joint Laboratory of Environment Simulation and Pollution Control, School of Environment, Beijing Normal University , Xinjiekouwai Street No. 19, Beijing 100875, China.
authors.forename: Yan
authors.initials: Y
authors.lastname: Zhang
authors.affiliation: State Key Joint Laboratory of Environment Simulation and Pollution Control, School of Environment, Beijing Normal University , Xinjiekouwai Street No. 19, Beijing 100875, China.
authors.forename: Hanjing
authors.initials: H
authors.lastname: Lu
authors.affiliation: Department of Biological Sciences, Towson University , Towson, Maryland 21252, United States.|Dynamic Systems, International Institute for Applied Systems Analysis , Laxenburg, Austria.
authors.forename: Brian D
authors.initials: BD
authors.lastname: Fath
authors.affiliation: State Key Joint Laboratory of Environment Simulation and Pollution Control, School of Environment, Beijing Normal University , Xinjiekouwai Street No. 19, Beijing 100875, China.
authors.forename: Hongmei
authors.initials: H
authors.lastname: Zheng
authors.affiliation: State Key Joint Laboratory of Environment Simulation and Pollution Control, School of Environment, Beijing Normal University , Xinjiekouwai Street No. 19, Beijing 100875, China.
authors.forename: Xiaoxi
authors.initials: X
authors.lastname: Sun
authors.affiliation: State Key Joint Laboratory of Environment Simulation and Pollution Control, School of Environment, Beijing Normal University , Xinjiekouwai Street No. 19, Beijing 100875, China.
authors.forename: Yanxian
authors.initials: Y
authors.lastname: Li
mesh_terms: D000068476:Beijing; D004785:Environmental Pollutants / Q000378:metabolism*; D009584:Nitrogen / Q000378:metabolism*; D012722:Sewage / Q000032:analysis; D014186:Transportation; D014507:Urbanization
chemical_list: D004785:Environmental Pollutants; D012722:Sewage; D009584:Nitrogen