Diffuse pollution

• Stretches of rivers in the South West recording high phosphate concentrations have reduced from 54% in 1990 to 43% in 2007.
• Stretches recording high nitrate concentrations increased from 22% in 1990 to 26% in 2007. 
• Large areas of the region have been designated as Nitrate Vulnerable Zones to reduce nitrate use by farming.  Nitrate Vulnerable Zones will cover almost 50% of the South West. 

Diffuse pollution can arise from many sources, which are generally dispersed and diverse in nature. It is derived from current and past land use in both rural and urban environments. The sources may individually be small but their collective impact can be damaging. It can have a significant impact on the environment in terms of both wildlife and our use of it.

Diffuse pollution can have significant effects on wildlife and our use of water, such as contamination of groundwater, surface water and drinking water supplies. It can also cause the smothering of fish spawning gravels, eutrophication, oxygen depletion and can be toxic to plant and animal life.

The Water Framework Directive (WFD) came into force on 22 December 2000. It requires all inland and coastal waters to reach "good status" by 2015. Water quality in the UK has improved significantly in recent years, but diffuse sources of pollution remain a concern. Many rivers and lakes could fail to meet the "good status" objectives because of diffuse water pollution from agriculture.

Excessive nitrate can also disturb the delicate ecological balance of inland and coastal waters, causing eutrophication, which can lead to devastating algal blooms. These blooms can very quickly remove all the oxygen, killing animal and plant life in the water. Some algae can also be poisonous to livestock and pets of they drink the water.

Nitrate concentrations in rivers and groundwater have increased substantially since the 1940s. These increases are mainly due to changing agricultural practices, such as using nitrogen fertiliser to grow higher yielding crops. As more nitrates are put onto the land, more become washed away into rivers and groundwater.  About 60% of the nitrate in surface and groundwater comes from agriculture. The other significant sources of nitrate are sewage effluent and deposition from the air.

Groundwater is used in the South West as a source of drinking water for public and private supplies. Monitoring shows that nitrate levels in groundwater have been steadily rising over the past few years as a result of the application of manure and fertilisers to farmland. Subsequently, large areas of the region have been designated as Nitrate Vulnerable Zones to reduce nitrate use by farming in these areas.  Nitrate Vulnerable Zones will cover almost 50% of the South West.  This will require farmers to have an action programme of improvement measures including the storage of slurries for longer periods over the autumn and winter. Newly designated NVZs will need to comply with this by January 2010.

Nitrate concentrations in rivers and groundwater have increased substantially since the 1940s. These increases are due to changing agricultural practices, such as using nitrogen fertiliser to grow higher yielding crops. As more nitrates are put onto the land, more become washed away into rivers and groundwater.  In 2007, 54% of English rivers had high concentrations of phosphate compared with 69% in 1990 and 10% of Welsh rivers had high concentrations of phosphate, compared 26% in 1990.  High concentrations of nitrate were found in 32% of English rivers compared with 36% in 1995. High concentrations of nitrate rarely occur in Welsh rivers. The Environment Agency website has further details.

Stretches of rivers in the South West recording high Phosphate concentrations have reduced from 54% in 1990 to 43% in 2007. However stretches recording high nitrate concentrations have increased from 22% in 1990 to 26% in 2007.  Generally  the rivers in the East of the region record higher concentrations. 25% of the rivers in South West are graded high or very high. A further 30% are graded as having moderate concentrations. Only 16% of river stretches are graded low or very low.  Rivers in the east part of the region record the highest phosphate concentrations. 42% of rivers in the region were graded between high and excessively high. 18% were graded with very low concentrations, many of these stretches of rivers can be found on Dartmoor & Exmoor.  See river water quality for more details.

A number of South West river catchments should support healthy populations of salmon but surveys show that numbers are lower than expected. One factor considered to be contributing to the poor population numbers is sediment eroded from field surfaces and from along river banks which can smother river gravels and reduce feeding success.

Chemicals used in farming as pesticides and herbicides are detected in both surface and groundwater in the South West. Although levels detected are lower than what would be considered to be toxic to aquatic life, where the water is abstracted for use as drinking water, additional treatment of the water has to be provided by the water companies to ensure the water is fit to drink.

• Environment Agency water quality
• Environment Agency Nitrate Vulnerable Zones
• Defra - Nitrates, reducing water pollution from agriculture