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Nitrogen Cycles: Past, Present, and Future
Authors:J N Galloway  F J Dentener  D G Capone  E W Boyer  R W Howarth  S P Seitzinger  G P Asner  C C Cleveland  P A Green  E A Holland  D M Karl  A F Michaels  J H Porter  A R Townsend  C J Vöosmarty
Institution:(1) Environmental Sciences Department, University of Virginia, Charlottesville, 22903, USA;(2) Joint Research Centre, Institute for Environment and Sustainability Climate Change Unit, Ispra, Italy;(3) Wrigley Institute for Environmental Studies, University of Southern California, Los Angeles, California, USA;(4) College of Environmental Science and Forestry, State University of New York, Syracuse, New York, USA;(5) Department of Ecology & Evolutionary Biology, Cornell University, Ithaca, New York, USA;(6) Institute of Marine and Coastal Sciences, Rutgers, The State University of New Jersey, New Brunswick, New Jersey, USA;(7) Department of Global Ecology, Carnegie Institution, Stanford University, Stanford, California, USA;(8) Institute of Arctic and Alpine Research, University of Colorado, Boulder, Colorado, USA;(9) Complex Systems Research Center, Institute for the Study of Earth, Oceans, and Space, University of New Hampshire, Durham, New Hampshire, USA;(10) Atmospheric Chemistry Division, National Center for Atmospheric Research, Boulder, Colorado, USA;(11) Environmental Sciences Department, University of Virginia, Charlottesville, 22903, USA
Abstract:This paper contrasts the natural and anthropogenic controls on the conversion of unreactive N2 to more reactive forms of nitrogen (Nr). A variety of data sets are used to construct global N budgets for 1860 and the early 1990s and to make projections for the global N budget in 2050. Regional N budgets for Asia, North America, and other major regions for the early 1990s, as well as the marine N budget, are presented to Highlight the dominant fluxes of nitrogen in each region. Important findings are that human activities increasingly dominate the N budget at the global and at most regional scales, the terrestrial and open ocean N budgets are essentially disconnected, and the fixed forms of N are accumulating in most environmental reservoirs. The largest uncertainties in our understanding of the N budget at most scales are the rates of natural biological nitrogen fixation, the amount of Nr storage in most environmental reservoirs, and the production rates of N2 by denitrification.
Keywords:nitrogen  Haber-Bosch  fertilizer  fossil fuel combustion  denitrification  nitrogen fixation
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