e-Digest Statistics about: Inland Water Quality and Use
Freshwater quality
Oxygen and ammonia
Table 8a, Table 8b and Table 8c illustrates the annual average concentrations and the maximum and minimum site means for 1980-2004 for three determinands: dissolved oxygen, biochemical oxygen demand (BOD) and ammoniacal nitrogen as measured at sites within the Harmonised Monitoring Scheme (HMS). The amount of oxygen dissolved in water is a test of the ability of the water to support aquatic life, with higher amounts generally indicating better water quality. BOD measures the amount of oxygen consumed in water, usually by organic pollution, so lower values indicate better quality.
Ammoniacal nitrogen is often found in water as a result of the discharge of sewage effluent and high levels adversely affect the quality of water for fisheries. These three determinands are amongst those which are sampled most frequently and consistently and form the basis of the classification used for the national river quality surveys. However, there is no direct correspondence between average values of these individual determinands (given in Table 8a, Table 8b and Table 8c) and the national river quality classifications (in Table 4 and Table 5). This is because a chemical GQA grade is determined by the amount of each of the three determinands present in the sampled water. In addition, the HMS sites are only a small fraction of the total number of monitoring sites in England and Wales.
In Detail:
Further Information:
Data Tables:
- Internet Links:
- For national and local information see:
- Department of the Environment in Northern Ireland
- England and Wales, Water Quality: Environment Agency - River quality
- Scotland: Scottish Environment Protection Agency - Environmental Data : Classification Scheme
- Northern Ireland: Environment and Heritage Service - River Water Quality Monitoring
- Department of the Environment in Northern Ireland
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Page last modified: 31 January 2006
Page published: 7 December 2004