Water, Air, & Soil Pollution: Focus

, Volume 7, Issue 1–3, pp 413–419

The Applicability of National Critical Loads Data in Assessing Designated Sites

  • Jane Hall
  • Jackie Ullyett
  • Richard Wadsworth
  • Brian Reynolds


Critical loads have been successfully used within Europe in the development of effects-based policies for pollution abatement, including the Second Sulphur Protocol and the Protocol to abate acidification, eutrophication and ground-level ozone (CLRTAP, 1979). This success has encouraged the UK Environment Agency and Conservation Agencies to use the national critical load maps as a screening tool in assessing the threats from acidification and eutrophication to designated (Natura 2000) sites. The UK maps of critical loads are based on national-scale data sets appropriate for national-scale assessments, and were never intended for use at the site-specific level. Site-based assessments are often targeted at Special Areas of Conservation, a sub-set of the UK Natura 2000 sites. The spatial data available includes the boundaries of the sites but not the location of the designated features. Ancillary data is variable from one site to another; habitat types may be described in detail with cross-reference to classes of the National Vegetation Classification (NVC: Rodwell, 1991 et seq), but information available on soils and geology is generalised and has not been related to the habitats or species being protected. Hence it can be difficult to relate the individual sites to the national maps, even where appropriate to do so. This paper examines the underlying uncertainties in the national critical load maps showing how the maps could give misleading results if used for site-specific assessments. It also includes advice on how to determine when the national data may be appropriate as a policy-tool at the site-level.


critical loads designated sites endorsement theory national vegetation classification policy acidification eutrophication 


  1. Calver, L. J., Cresser, M. S., & Smart, R. P. (2004). Tolerance of Calluna vulgaris and peatland plant communities to sulphuric acid deposition. Chemistry and Ecology, 20, 309–320.CrossRefGoogle Scholar
  2. CLRTAP (1979). Protocols to the convention on long-range transboundary air pollution. Geneva, Switzerland: United Nations Economic Commission for Europe.Google Scholar
  3. Cohen, P. R. (1985). Heuristic reasoning about uncertainty: An artificial intelligence approach. Boston: Pitman.Google Scholar
  4. Dempster, A. P. (1967). Upper and lower probabilities induced by a multi-valued mapping. Annals of Mathematical Statistics, 38, 325–339.Google Scholar
  5. DETR (2000). The air quality strategy for England, Scotland, Wales and Northern Ireland – Working together for clean air. London, UK: Department of the Environment, Transport and the Regions.Google Scholar
  6. EU (1992). Council Directive 92/43/EEC of 21 May 1992 on the conservation of natural habitats and of wild fauna and flora. http://europa.eu.int/comm/environment/nature.
  7. Hall, J., Ullyett, J., Heywood, L., Broughton, R., Fawehinmi, J., & 31 UK experts (2003). Status of UK critical loads: Critical loads methods, data and maps. February 2003. Report to Defra (Contract EPG 1/3/185). http://critloads.ceh.ac.uk.
  8. Hall, J., Ullyett, J., Heywood, L., Broughton, R., & 12 UK experts (2004a). Update to: The status of UK critical loads – Critical loads methods, data and maps. February 2004. Report to Defra (Contract EPG 1/3/185). http://critloads.ceh.ac.uk.
  9. Hall, J., Ullyett, J., Heywood, L., Broughton, R., & Fawehinmi, J. (2004b). The National Critical Loads Mapping Programme Phase IV. Final report to Defra: July 2001–June 2004 (Contract EPG 1/3/185).Google Scholar
  10. Heywood, E., Skeffington, R., Whitehead, P., & Reynolds, B. (this issue). Comparison of critical load exceedance and their uncertainties based on national and site-specific inputs.Google Scholar
  11. Hornung, M., Bull, K. R., Cresser, M., Hall, J., Langan, S. J., Loveland, P. et al. (1995). An empirical map of critical loads for acidity in Great Britain. Environmental Pollution, 90, 301–310.CrossRefGoogle Scholar
  12. Langan, S. J., Hall, J., Reynolds, B., Broadmeadow, M., Hornung, M., & Cresser, M. S. (2004). The development of an approach to assess critical loads of acidity for woodland habitats in Great Britain. Hydrology and Earth System Sciences, 8, 355–365.CrossRefGoogle Scholar
  13. Loveland, P. J. (1991). The classification of the soils of England and Wales on the basis of mineralogy and weathering – The Skokloster approach. A report to the Department of the Environment under Research Contract Reference no. PECD 7/12/44.Google Scholar
  14. Rodwell, J. S. (Ed.) (1991). British plant communities, 5 volumes. Cambridge: Cambridge University Press.Google Scholar
  15. Shafer, G. (1976). Mathematical theory of evidence. Princeton, N. J., USA: Princeton University Press.Google Scholar
  16. Skeffington, R., Hall, J., Heywood, E., Wadsworth, R. A., Whitehead, P., Reynolds, B. et al. (2005). Uncertainty in critical load assessment models. Final report to the Environment Agency. R&D Project no. P4-120/4: Acidification and Annual Audits. December 2005. 152 pages.Google Scholar
  17. UBA (2004). Manual on methodologies and criteria for modelling and mapping critical loads & levels and air pollution effects, risks and trends. Texte 52/04 (ISSN 0722-186X), Umweltbundesamt, Berlin. http://www.oekodata.com/icpmapping.
  18. Wadsworth, R. A., & Hall, J. (this issue). Using endorsement theory and Dempster–Shafer formalism to reason with uncertain and incomplete information.Google Scholar

Copyright information

© Springer Science+Business Media B.V. 2007

Authors and Affiliations

  • Jane Hall
    • 1
  • Jackie Ullyett
    • 1
  • Richard Wadsworth
    • 1
  • Brian Reynolds
    • 2
  1. 1.Centre for Ecology and HydrologyHuntingdonUK
  2. 2.Centre for Ecology and HydrologyBangorUK

Personalised recommendations