The critical loads and levels approach for nitrogen

Thomas A. Clair, Tamara Blett, Julian Aherne, Marcos P.M. Aidar, Richard Artz, William J. Bealey, William Budd, J. Neil Cape, Chris J. Curtis, Lei Duan, Mark E. Fenn, Peter Groffman, Richard Haeuber, Jane R. Hall, Jean Paul Hettelingh, Danilo LÓpez-Hernändez, Scot Mathieson, Linda Pardo, Maximilian Posch, Richard V. PouyatTill Spranger, Harald Sverdrup, Hans Van Dobben, Arjan Van Hinsberg

Research output: Chapter in Book/Report/Conference proceedingChapterpeer-review

1 Citation (Scopus)


This chapter reports the findings of a Working Group to review the critical loads (CLs) and levels approach for nitrogen (N). The three main approaches to estimating CLs are empirical, mass balance and dynamic modelling. Examples are given of recent developments in Europe, North America and Asia and it is concluded that other countries should be encouraged to develop basic assessments using soil, land cover, and deposition map overlays in order to determine what regions might exceed nitrogen CLs. There is a need for increasing the certainty of critical load (CL) estimates by focusing on empirical data needs, especially for understudied ecosystems such as tropical or Mediterranean, high elevation environments, and aquatic systems. There is also a need to improve steady-state mass balance parameters, especially soil solution terms, such as nitrate leaching, used to determine the CL, and denitrification, which is an equation parameter. Improved dynamic models are needed for predicting plant community changes, and work should continue on existing models to determine CL values. Dynamic models require more data and are more complex than simple calculated CLs but offer more information and allow the development of ’what if?’ scenarios. Optimal use of CLs requires expert knowledge of ecosystem values to provide reference states so that safe deposition amounts can be determined. Increased interaction between CL and biodiversity specialists to identify critical biodiversity limits would help provide better CL assessments.

Original languageEnglish
Title of host publicationNitrogen Deposition, Critical Loads and Biodiversity
Subtitle of host publicationProceedings of the International Nitrogen Initiative Workshop, Linking Experts of the Convention on Long-Range Transboundary Air Pollution and the Convention on Biological Diversity
PublisherSpringer Netherlands
Number of pages11
ISBN (Electronic)9789400779396
ISBN (Print)9789400779389
Publication statusPublished - 1 Jan 2014
Externally publishedYes


  • Critical loads
  • Empirical
  • Exceedance
  • Modelling
  • Nitrogen deposition

ASJC Scopus subject areas

  • General Environmental Science


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