If you need an accessible version of this item please contact JSTOR User Support

Human Impacts on the Nitrogen Cycle: A Global Problem Judged from a Local Perspective

Dag O. Hessen, Arne Henriksen, Atle Hindar, Jan Mulder, Kjetil Tørseth and Nils Vagstad
Ambio
Vol. 26, No. 5, Nitrogen from Mountains to Fjords (Aug., 1997), pp. 321-325
Published by: Springer on behalf of Royal Swedish Academy of Sciences
Stable URL: http://www.jstor.org/stable/4314610
Page Count: 5
  • Download PDF
  • Cite this Item

You are not currently logged in.

Access your personal account or get JSTOR access through your library or other institution:

login

Log in to your personal account or through your institution.

If you need an accessible version of this item please contact JSTOR User Support
Human Impacts on the Nitrogen Cycle: A Global Problem Judged from a Local Perspective
Preview not available

Abstract

This chapter revisits the major problems relating to man-made disturbances in the global nitrogen (N) cycle, and links the local findings from the project to the large-scale effects. The human transformation of atmospheric N2 to chemically and biologically more reactive species causes a number of environmental effects. The focus of this project has been budget estimates of N for two large watersheds with a set of subcatchments in southern Norway, accompanied by process studies to explain patterns of retention and runoff of N. Atmospheric inputs were close to 2.5 mg N m-2 yr-1 and by far the dominant source of N for the sparsely populated, heathland dominated watershed. Low retention and apparent N saturation could be accredited to high atmospheric inputs of N, but also hydrology, poorly developed soils and terrestrial P limitation. In this acidified watershed, nitrate contributed nearly 50% to surface water acidification, underlining the importance for strong cuts in NO x and ${\rm NH}_{{\rm x}}$ emissions. P concentrations were low, frequently $<1\ \mu {\rm g}\ {\rm L}^{-1}$, causing high N:P ratios in runoff, and promoting P limitation both in freshwater and the nearshore marine recipient. For the agriculturally and forested watershed, atmospheric N deposition was < 1.5 mg N m-2 yr-1, and agricultural activities were the totally dominant source of N, yielding generally high but fluctuating concentrations of N and P in runoff water. Forestry and agricultural practices were major determinants of N runoff. The high concentrations of both N and P in the major outlet of this watershed would be a major source of eutrophication for the recipient fjord. For both watersheds, climatic fluctuations strongly affected annual runoff patterns of N. The fate of ammonium relative to nitrate and long-term climatic changes with a possible mineralization of soil stores of organic N are unpredictable determinants to future effects of N.

Page Thumbnails

  • Thumbnail: Page 
321
    321
  • Thumbnail: Page 
322
    322
  • Thumbnail: Page 
323
    323
  • Thumbnail: Page 
324
    324
  • Thumbnail: Page 
325
    325