e-Digest Statistics about: Inland Water Quality and Use
Influences on freshwater quality and their control
Acidification
The critical loads approach is an effects-based method of assessing the impact of acid deposition on ecosystems or species [20]. Critical loads are defined as the deposition load below which significant harmful effects do not occur according to present knowledge [21]. The map in Figure 5 shows the areas in the UK where critical loads of acidity for freshwaters are exceeded by annual mean total acid deposition (ie, sulphur plus oxidised and reduced nitrogen deposition) for the period 1999-2001. The map shows the critical load exceedances for 1722 freshwater sites sampled across the UK, representing an area (ie, the sum of all catchments sampled) of 7791 km². It is estimated that 23.2% of this area is exceeded by the 1999-2001 levels of acid deposition [22].
Since March 2004, freshwater critical loads have been calculated to maintain surface water acid neutralizing capacity (ANC) above 20 microequivalents per litre to protect sensitive aquatic species, except for a few water bodies where site specific studies indicated that pre-industrial (i.e. "natural") ANC values may have been lower, in which case a critical ANC of zero microequivalents per litre is used.
Future of Britain's Upland Waters
The Freshwater Umbrella research programme into the recovery of aquatic ecosystems from the effects of acidification has been funded by Defra and the devolved agencies since 1990. The Freshwater Umbrella undertakes 3-year applied science programmes to develop the scientific background to aid Defra make policy decisions concerned with air pollution effects on freshwater systems in the UK.
The main focus of the current Freshwater Umbrella research programme is the role of nitrogen and its effects on freshwater ecosystems both as a eutrophier and through the leaching of nitrate from catchment soils. Further information about the various research programmes undertaken by the Freshwater Umbrella can be found in the Research section of the website.
The United Kingdom Acid Waters Monitoring Network (UKAWMN), funded by the Defra, and the Department of the Environment Northern Ireland, was established in 1988 to monitor the ecological impact of acid deposition in areas of the UK believed to be sensitive to acidification. Over a decade on, its data-base provides a long-term record of water chemistry and biology which is unique for upland freshwater systems in the UK.
In Detail:
- e-Digest: Air Quality: Acid deposition
Further Information:
- References, further reading and links to other resources:
- [20] Mapping Manual 2004. UNECE Convention on Long-range Transboundary Air Pollution. Manual on methodologies and criteria for modelling and mapping critical loads and levels and air pollution effects, risks and trends. http://www.icpmapping.org
- [21] Critical loads for sulphur and nitrogen. Report 1988:15. UNECE/Nordic Council of Ministers, Copenhagen, Denmark. Nilsson, J. & Grennfelt. P. (Eds.) 1988.
- [22] Addendum to Status of UK critical loads: The status of UK critical load exceedances. April 2004. Report to Defra (Contract EPG 1/3/185). Hall, J., Ullyett, J., Heywood, L., Broughton, R. & Fawehinmi, J. 2004. http://critloads.ceh.ac.uk
- Internet Links:
- For national and local information see:
- United Kingdom National Focal Centre (UK NFC) for critical loads modelling and mapping, CEH Monks Wood
- University College London, Freshwater Umbrella
- United Kingdom Acid Waters Monitoring Network (UKAWMN)
Your questions and comments about information presented on this page are welcome. Contact information and Email . Copyright of data and/or information presented or attached in this document may not reside solely with this Department. Please see guidance on Copyright.
Page last modified: 6 February 2006
Page published: 23 December 2004