Examples from Europe and Canada

In 1984, a protocol to the UNECE 1979 Convention on Long-Range Transboundary Air Pollution was established providing for long-term financing of the Cooperative Program for Monitoring and Evaluation of the Long-Range Transmission of Air-Pollutants in EUROPE (EMEP) (http://www.unece.org/env/lrtap/emep_h1.htm). This protocol permitted the development of the scientific and administrative structure necessary for coordinated evaluation of critical loads and exceedances for acidifying pollutants in Europe. For over a decade, European countries have used the critical loads concept to set emissions reduction targets for S and N under the UNECE Convention on Long-Range Transboundary Air Pollution (Posch and others 1995). Initially, the critical loads for S and N were developed for effects on fresh-water aquatic ecosystems. This work was rapidly expanded to include the developing understanding of the role of S and N deposition in producing European forest declines.

Canada followed Europe’s lead and developed critical loads modeling programs first for aquatic and then forest ecosystems (Ouimet and others 2001, Ouimet and others 2006) that have been incorporated into the periodic Canadian Acid Rain Assessments (Morrison and others 2005). Until recently, few have attempted to apply the critical loads approach to large forest landscapes in the United States.