ARCHIVE: Background: agriculture and diffuse water pollution
- How does agriculture contribute to diffuse pollution?
- What is eutrophication?
- How is diffuse water pollution from agriculture being addressed?
Some water pollution can be attributed to a "point source", such as discharges from sewage treatment works or industries. Over the past 15 years considerable progress has been made in addressing these point sources of water pollution. For example, implementation of the Urban Waste Water Treatment Directive has led to significant investment by water companies in the treatment of discharges from sewage treatment works.
Diffuse water pollution, in contrast, cannot be attributed to a precise point or incident. Rather, it is the cumulative effect of day to day activity over a large area. Various activities contribute to diffuse pollution, including agriculture, forestry, mining, construction and urban life. Pollutants deposited on land, roads and spaces are washed into watercourses by rain. Consequently, the local climate, geology and other natural phenomena can influence the size and extent of the problem. In agriculture, diffuse pollutants include silt from soil erosion, nutrients from the application of fertiliser or spreading of manure, and pesticides from the handling and application of the chemicals.
We need to start making progress on addressing diffuse sources of water pollution which – whether from agricultural or non-agricultural sources – have been identified as the major risk to the quality of our water bodies.
No one farmer is responsible, and many are committed to protecting and enhancing the environment, but cumulatively diffuse pollution from farms is having a substantial impact on the quality of English waters.
- Around 60% of nitrate and 25% of phosphates in English waters originate from agricultural land. Elevated levels of these nutrients are of concern because they can cause eutrophication, which harms the water environment. Also, excess nitrate has to be removed before water can be supplied to consumers.
- Agriculture contributes between 25 – 50% of the pathogen loadings which affect England's bathing waters.
- Up to 75% of sediment input into rivers can be attributed to agriculture. This reduces water clarity and causes serious problems for fish, plants and insects.
- Pesticides are contaminating drinking water sources, requiring expensive treatment at water works to remove pesticides before it is supplied to consumers.
Eutrophication is the enrichment of water by nutrients (such as nitrate or phosphate), causing an accelerated growth of algae and higher forms of plant life leading to an undesirable disturbance to the balance of organisms present in the water and to the quality of the water concerned.
The resulting disturbed aquatic ecosystem may:
- become an unsuitable habitat for other species such as fish and invertebrates. This reduces biodiversity of both the aquatic habitat and of other species in the food chain;
- become too low in oxygen for some species to tolerate, such as fish and shellfish;
- damage the quality of areas of high wildlife conservation value, such as Sites of Special Scientific Interest (SSSIs);
- produce toxic algal blooms which poison fish and shellfish, making them unsafe for people to eat and damaging the fisheries industry. However, there is as yet no well-established link between nutrient enrichment and the incidences of shellfish toxicity in marine waters. Local livestock and wildlife may be at risk and blooms in recreational waters can result in closure of the area, with impacts on tourism;
- produce so much vegetation that navigation or recreational use of waters becomes impossible. This also impacts on the tourism and leisure industry.
Part of what we need to achieve is the improved control of the application of manures and fertilisers to land. We are looking at ways of achieving this improvement, for example through:
- promoting the Codes of Good Agricultural Practice
- encouraging Catchment sensitive farming - managing land in a way that is sensitive to the ecological health of the water environment.
- Implementing the EC Nitrates Directive
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Page last modified: 19 March 2008
Page published 27 June 2002