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Individual Highlight

Determining What Levels of Air Pollution Harm U.S. Ecosystems

Forested ecosystem in the White Mountains of New Hampshire. Ken Dudzik, Forest ServiceSnapshot : An international team led by a Forest Service scientist has determined the level of nitrogen (N) deposited from air pollution that harms ecosystems across the United States. This research provides an assessment tool for managers and policy makers to use when making decisions about limiting N pollution to protect vulnerable ecosystems.

Principal Investigators(s) :
Pardo, Linda 
Research Station : Northern Research Station (NRS)
Year : 2011
Highlight ID : 326


Nitrogen (N) deposition from air pollution has reached a level that has caused, or is likely to cause, alterations and damage in ecosystems across the United States. An international team led by a Forest Service scientist determined the critical N load, that is, the level of N deposition below which no detrimental ecological effects occur. The team synthesized current research relating atmospheric N deposition to effects in terrestrial and aquatic ecosystems. Responses to increased N deposition included changes in biological community structure, altered soil N cycling, increased N leaching to soil and surface waters, increases in susceptibility to secondary stresses, increases in invasive species, and altered fire regimes. The range of critical loads for nutrient N reported for U.S. ecoregions, inland surface waters, and wetlands is 1 to 39 kg of N/ha annually. In many regions, the critical load for sensitive receptors has been exceeded. The critical loads approach is an ecosystem assessment tool with great potential to simplify complex scientific information and provide a scientific basis for making decisions about limiting air pollution to protect vulnerable ecosystems.

Forest Service Partners

External Partners

  • And Robert Johnson, University of California, Riverside who created the critical loads and exceedance maps.
  • Bridget Emmett, CEH, United Kingdom
  • Charles Driscoll, Syracuse University, Edith Allen, University of California, Riverside
  • Christine Goodale, Cornell University
  • Christopher Clark, Tara Greaver, Lingli Liu, Jason Lynch, and John Stoddard, U.S. EPA
  • Frank Gilliam, Marshall University
  • Jill Baron and Steve Perakis, USGS
  • Kathleen Weathers, Cary Institute of Ecosystem Studies
  • Knute Nadelhoffer, University of Michigan
  • Roland Bobbink, B-WARE Research Center, the Netherlands
  • Sharon Hall, Arizona State University
  • William Bowman, University of Colorado