e-Digest Statistics about: Inland Water Quality and Use
Freshwater quality
Variations in rainfall and river flow can have a considerable effect on freshwater quality [3]. Overall, lower than average rainfall and low river flows can have an adverse effect on river quality because there is reduced dilution of pollutants. At low flows and warm temperatures, algae can grow more. The presence of algae affect dissolved oxygen concentrations and biological oxygen demand (BOD) in rivers. On the other hand, effluent treatment works better in hot dry weather, and river quality benefits from fewer storms. High rainfall can also adversely affect quality by causing greater leaching of potential pollutants from the soil into fresh waters and, in periods of intense rainfall, the operation of overflows from the sewerage system. However, increased river flows can also lead to greater dilution of contaminants.
Chemical river quality surveys
The chemical quality of rivers and canal waters in the United Kingdom has been monitored in a series of separate national surveys in England and Wales [4], Scotland [5] and Northern Ireland [6]. Summary results for chemical surveys undertaken in each country since 1990 are shown in Table 4a and Table 4b. However, different systems of classification have been used in these national surveys so the results are not directly comparable across countries.
The General Quality Assessment (GQA) Scheme [4] assesses the basic chemical quality of rivers and canals based on three determinands - dissolved oxygen, biochemical oxygen demand (BOD) and ammoniacal nitrogen. It is used to assess chemical quality of rivers and canals across England and Wales at 7,000 sites representing 40,000 kilometres of fresh waters since 1990. The GQA grades river stretches into six categories (A - F) of chemical quality and these in turn have been grouped into four broader groups - good, fair, poor and bad. The GQA methodology and grades as used in England and Wales are described in more detail on the Environment Agency web site at the address given below.
Since 1991, the Northern Ireland Environment and Heritage Service has also used the GQA Scheme for classification. The coverage of the Northern Ireland monitoring system was extended considerably from just under 1,700 km of rivers surveyed in 1991 to over 4,300 km in 2003. The majority of the additional lengths were small rivers or streams.
Table 4a and Table 4b also show the quality of monitored river lengths in Scotland between 1990 and 2006. In 1996 the Scottish Environment Protection Agency (SEPA) introduced a new classification scheme which involves an assessment of chemical, biological, nutrient and aesthetic measures of environmental quality. The change in classification means that the scope to look at trends in river quality over the period 1990-2006 is limited. In 2000 Scotland introduced a new system for recording river and stream lengths called the Digitised Rivers Network (DRN). The classification scheme remains the same but the DRN includes rivers on islands and does not include thousands of minor, sometimes seasonally dry, and generally remote headwater tributaries that have never been monitored.
Table 5a shows the chemical GQA grade of rivers and canals in England and Wales by EA region and Northern Ireland and percentages of rivers classified as good, fair, poor and bad. Table 5b shows the combined classification of rivers and canals in Scotland by region and percentages of rivers classified as 'good or fair' and 'poor or seriously polluted' for 1996 to 2000. Data based on the new Scottish network for 2000 to 2006 are shown in table Table 5c.
The River Water Quality Database provides chemical, biological and nutrient data on monitored rivers for each Government Office Region and Local Authority in England and Wales. Chemical data are available for 1990, 1993-2006.
Whilst the 1990 baseline was influenced to some extent by the effects of unusually low summer rainfall in 1989 and 1990 the improvements in water quality since 1990 are believed to be attributable largely to the positive impact of the investment programme of the water industry and pollution control measures.
These chemical water quality survey assessments have been adopted, along with biological quality assessments, as part of the river quality framework indicator for sustainable development. The 20 framework indicators associated with the new UK Framework for sustainable development are intended to give an overview of progress on key issues common to the sustainable development strategies of the UK government and the Devolved Administrations. They fulfil a similar role to the former 15 headline indicators of the old sustainable development strategy. The water quality framework indicator is similar to the old water quality headline except that it now focuses on 'good' quality rather than 'good or fair' quality. For further details of the latest version of the indicator, see the press release below, or visit the Sustainable Development web site.
Future quality assessment
The current regime of chemical water quality assessment originated in the 1970s, and biological monitoring developed in the 1980s and 90s. These monitoring systems are mainly geared to measuring pollution from point sources (such as discharges from factories or sewage works), although they do also detect some diffuse pollution (for example from agriculture or from roads or urban areas).
The UK is now implementing the EU Water Framework Directive, which for the first time uses the ecology of waters bodies as the main indicator of quality, and takes into account a wider range of pressures on water quality - point sources; diffuse pollution; water abstraction; physical alterations (such as land reclamation, flood defences, or river straightening) or invasive alien species. This will represent a step change in the assessment of water quality.
The Directive requires that all inland and coastal water bodies reach at least "good” status by 2015 - subject to certain exemptions, which allow alternative objectives to be set in cases where it is technically infeasible or disproportionately expensive to achieve good status. It is doing this by establishing a “river basin planning” process, based on a “river basin district” structure, within which demanding environmental objectives have been set, including ecological targets for surface waters. The monitoring process also covers a wider range of quality measures than before.
Within each river basin district, the Directive requires that a "river basin management plan" is established and updated every six years. The Directive therefore sets a framework which should provide substantial benefits for the long term sustainable management of water. Within the UK, it is expected that the Water Framework Directive will:
- improve inland and coastal waters, and reduce diffuse pollution in urban and rural areas, especially through better land management;
- drive wiser, sustainable use of water as a natural resource; and
- create better habitats for wildlife that lives in and around water
he Directive came into force on 22nd December 2000. In accordance with the agreed implementation timetable, monitoring under the Directive commenced on 22nd December 2006.
In Detail:
- River Water Quality Database providing data on chemical and biological river water quality and nutrient concentrations for each Government Office Region and Local Authority in England and Wales.
- Biological river quality surveys
- Chemical river quality surveys
- Groundwater quality
Further Information:
- Press Release:
- River Water Quality framework indicator for Sustainable Development: 2006, 28 August 2007 (272/07)
- Sustainable Development Indicators:
- Framework Indicators: River water quality
- Explanation of indicators
Data Tables:
- References, further reading and links to other resources:
- [3] The State of the Environment of England and Wales: Freshwaters. Environment Agency, 1998. The Stationery Office, London.
- [4] Rivers and Estuaries - A Decade of Improvement. General Quality Assessment of Rivers and Estuary classification in England and Wales 2000. Environment Agency, January 2002
- [5] Improving Scotland's water environment. SEPA State of the Environment Report. The Scottish Environment Protection Agency, 1999
- [6] River Quality in Northern Ireland 1995. Department of the Environment for Northern Ireland, 1997
- [19] Department of the Environment, Transport and the Regions (1999), Quality of life counts: Indicators for a strategy for sustainable development for the United Kingdom. DETR. Website: Indicators for a strategy for sustainable development for the United Kingdom
- Internet Links:
- For further details of national monitoring programmes:
- Environment Agency for England and Wales: River quality
- Scottish Environment Protection Agency Environmental Data : Classification Scheme
- Northern Ireland: Environment and Heritage Service River Water Quality Monitoring
- For further details of the Water Framework Directive:
- Environment Agency for England and Wales
- Scottish Environment Protection Agency
- Northern Ireland: Environment and Heritage Service
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Page last modified: 28 August 2007
Page published: 28 August 2007