Diffuse Pollution
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.
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 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 2006, 28% of rivers in England and Wales had high concentrations of nitrate (greater than 30mg/l), which was slightly less than that found in 1995 or 2000. In the South West, 17.5% of the region's rivers had high concentrations of nitrate which was very slightly over the 17.7% found in 2000 but higher than the 15.4% recorded in 1995. Nitrate concentrations fluctuate year to year so there is no clear overall trend. Environment Agency, 2007
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.
More information about diffuse pollution is available from the South West Observatory Environment website. Diffuse pollution, bathing water quality and water quality are also indicators used to monitor progress of the Regional Environment Strategy.