Diffuse pollution
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Background
Diffuse pollution can arise from many sources, which are generally dispersed
and diverse in nature. Derived from current and past land use in both
agricultural and urban environments, sources may individually be small
but their collective impact can be damaging.
Diffuse pollution in the South
West
Diffuse water 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.
Between March 2001 and October 2005 there were 101 reported pollution
incidents to surface water that were from diffuse pollution sources. Most
commonly these incidents involved slurry runoff from agricultural yards
and fields. Four of these 101 incidents were serious enough to cause the
death of fish in affected rivers.
Nitrate levels in groundwater have been steadily rising over the past
few decades as a result of increased application of fertilisers on to
agricultural land. Subsequently, large areas in the region have been designated
as Nitrate Vulnerable Zones Levels of nitrate in the Lower Otter sandstone
in east Devon have increased from a mean value of 4.6 mg/l in 1992 to
8.3 mg/l in 2004 (nearly 80% increase) (Environment Agency).
As shown in the Nitrate General Quality Assessment (GQA) map, nitrates
in rivers are generally lower in Cornwall and Devon highest in Dorset,
Wiltshire and South Gloucestershire. This reflects the influence of the
nitrate contaminated groundwater on the quality of the surface water.
Nitrates in South West rivers 2004
click to enlarge
Source: Environment
Agency (2005)
In 2005, over 5.5 million hectares of land in the South West was treated
with pesticides, revealing a 25% increase since 1990.
Regular monitoring of river and groundwater abstracted for drinking water
by water companies in the region has found the presence of both pesticides
and herbicides, although at levels below the Environmental Quality Standard
set to protect aquatic life. The herbicide atrazine
is one of those that has been detected in our groundwater, which can feminise
male frogs.
Millions of pounds is spent by water companies in the region to remove
both nitrate and agricultural chemicals before our water is fit to drink.
103 of the 191 designated bathings waters
in the South West are also at risk of diffuse pollution from upstream
catchment sources. Since 2000, investigations at 15 of these bathing waters
have implicated that diffuse pollution has contributed to poor water quality.
Diffuse pollution from soils and runoff is one of the Environment
Agency's three key environmental issues in the South West region.
A more local perspective
16 case studies aimed at reducing diffuse water pollution from agriculture
in England have been highlighted in a recent report by Defra (2005). These
include the Cornwall Rivers Project, Cycleau Axe and Char project, Cycleau
Dart Catchment Project, Life into Landscape Project, Empool Project (Wessex
Water), Farm Environment Link Project, Hampshire Avon Landcare Project,
Helford Cycleau (Cornwall), Parrett Catchment Project, Tale Valley Project,
Tamar 2000 Support Project, Tone Project, Upper Torridge, WAGRICO –
Life Project, Wessex Chalk Rivers Project and West Country Rivers Project.
An example of these projects is the Cycleau
Axe and Char project, which aims to promote best farming practice
to reduce the impact of agriculture on watercourses and bathing waters
in catchments. Covering 300km2 of primarily agricultural land, the region
has seen an elevation in levels of nutrients, and increased sediment over
river gravels. There has also been increased soil and riverbank erosion,
a reduction in fish numbers and increased flooding. Key outcomes of this
project have so far shown a reduced likelihood of infringing regulations
as well as healthier soils as a result of the changing practices. There
has been improved water quality, protected spawning gravels, improved
soil structure, improved nutrient management and a reduction of pollution
incidents.
Another example is the Farm
Environment Link Project, which covers the whole of Cornwall. Intensive
agriculture, poor siting of gateways, poor timing for field works and
over application of nutrients have all added to the problem of silting
up of rivers, poor water quality, invertebrate absence and compaction
of soils. The project aims to enhance the economic sustainability of Cornish
agricultural holdings, which should result in a reduction in the levels
of phosphates and nitrates in local rivers. Key outcomes so far include
gross additional sales/costs saved was in excess of the project target
of £122,386. In excess of 2,500 ha of land are also subject to measures
to reduce soil erosion, flooding or other adverse effects from current
agricultural practice.
National perspective
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.
Pesticide use has increased as farming methods have intensified over
the last 50 years. Agriculture and horticulture use over 80% of all pesticides
in England and Wales. The most frequently occurring pesticide found in
groundwater in 2004 was Atrazine (Environment
Agency).
The vast majority of groundwater sample concentrations are below the
0.1 µg/l drinking water limit . Just over 5.4% of pesticides in
surface waters in England and Wales were above this drinking water limit
in 2004, roughly the same as in 2003 despite the wetter weather conditions
meaning that more pesticides could be washed into rivers (Environment
Agency).
According to the water industry (Water
UK), each water customer pays £7 a year for the removal of pesticides
and nitrates from drinking water, and this is likely to rise.
Improved regulation and our promotion of best practice on farms will
reduce the detrimental impact agricultural practices can have on the environment.
The Environment
Agency have more information about the reduction of pesticides in
rivers.
European and worldwide perspective
(where available)
Agriculture is the main source of diffuse pollution to water in Europe,
in particular nutrients such as nitrates and phosphates. More than half
of the nutrient discharges in Europe now come from diffuse sources arising
from farm fertiliser and manure.
Over the last 50 years, the rising use of commercial inorganic mineral
fertilisers and increased concentrations of livestock have resulted in
a sharp increase in the application of nutrients to the land.
(European
Environment Agency, 2005)
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