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2. DIFFUSE WATER POLLUTION FROM RURAL LAND USE IN SCOTLAND
2.1 Diffuse pollution
The nature of diffuse pollution has important implications for its control. Diffuse pollution typically arises from a multitude of small sources, such as poaching of river banks by livestock or run-off from forestry tracks, that are individually insignificant in terms of environmental impact but at a catchment scale can have a detrimental effect. Examples include the silting of salmonid spawning grounds or contribute to the progressive eutrophication of lakes. The transport of diffuse pollutants is also important. Pollutants often travel overland, mainly driven by rainfall events before reaching surface waters. For groundwater, diffuse pollutants are transported through the soil column and can take many years to become a noticeable problem.
For the control of diffuse pollution these characteristics mean practical methods of control are focused on land management practices, rather than traditional "end-of-pipe" regulation. The impacts of diffuse pollution are related to certain geographic, climatic and geological conditions and may differ greatly from place to place, resulting in the need for a targeted approach to pollution mitigation. The nature of diffuse pollution also means that environmental impacts and the success of control measures to address those impacts are measured on a catchment scale. This provides opportunities for community ownership of the problems and their solutions.
2.2 Pollutants and their impacts
Diffuse pollutants from agriculture and forestry include the nutrients nitrogen and phosphorus, pesticides and veterinary medicines, organic wastes, suspended solids (i.e. soil eroded from fields or forests) and faecal pathogens. Other chemicals such as oils and heavy metals can be important in some circumstances.
The impact of these pollutants is not uniform and may vary across the country dependent on a number of factors including;
- The nature of the receiving water body i.e. some water bodies are more sensitive to pollutant inputs than others.
- Climate - this effects the mobilisation of pollutants to watercourses and the dilution of pollutants in receiving water bodies.
- Soil type - depending on properties such as texture, soils can act as a sink or filter for pollutants.
- Land use - which is largely determined by the factors described above, affects the source and transport of pollutants.
Diffuse pollutants have a broad range of ecological and public health impacts, both of which can have considerable economic significance. Nutrients such as nitrogen (N) and phosphorus (P) can contribute to the process of eutrophication, when increased levels of algae consume the available oxygen, lowering the ability of the water to support aquatic life and making it unsuitable for other potential users. Organic substances, such as milk and manure, can also directly affect oxygen levels when they find their way into water, with subsequent impacts on aquatic life. Pollution from bacteria in animal manures can cause human health concerns either directly (ingestion when swimming) or indirectly (through contamination of fish/shellfish).
When eroded soil enters a watercourse, it becomes a pollutant in its own right, but it can also transport phosphorus and pesticides which are attached to soils to watercourses. Pollutant behaviour and subsequent transport affect the selection of mitigation methods. For example, the effectiveness of some mitigation measures is determined by the solubility of a pollutant.
2.3 Diffuse Pollution Impacts in Scotland
Land use and subsequent management play a fundamental role in the quality of Scotland's water environment. Over 70% of Scotland's area is defined as agricultural, the majority of which is rough grazing. Forestry is the second largest land use. Land use is largely determined by climate and soil type with arable agriculture typically being found along the drier East coast and grassland and associated livestock production in the wetter West. These regional and local variations have implications for the choice of control measures.
SEPA and its predecessor bodies have been measuring water quality for many years. The Water Framework Directive has called for a wide ranging characterisation of water bodies in terms of not achieving the Directive's environmental objectives. The results of the initial characterisation exercise have been published and are available electronically from http://www.sepa.org.uk/pdf/publications/wfd/Article_5_Scotland_River_Basin.pdf and, along with additional modelling data, form the evidence base described below, for the measures to mitigate diffuse pollution outlined in this consultation document.
It is estimated that diffuse pollution currently results in up to 43% of the water bodies in Scotland being at risk of not achieving good ecological status, and it is now a more significant source of pollution than point sources in most water bodies. This significant shift reflects the improvements in point source discharges brought about by more effective regulation.
Agriculture, due to its dominant land use, is a significant cause of diffuse water pollution in Scotland, although it may not be the most severe. Other important pressures are forestry and acidification. Figure 1 below shows the relative pressure per industry sector for diffuse pollution placing rivers at risk of failing to meet standards. Results for lochs, groundwater, transitional and coastal waters can be given. Agriculture is clearly the dominant pressure affecting rivers, while for lochs both agriculture and forestry are significant pressures. For transitional and coastal waters, agriculture is also the dominant pressure, although diffuse pollution from sea and coastal water transport are nearly as significant. For groundwater agriculture is again the most significant pressure, but diffuse pollution from urban areas and septic tanks is also significant.
Figure 1 Diffuse pressures on rivers in Scotland by sector. The category 'agriculture and forestry' is where further characterisation is required to split their relative contributions. 'Other' includes recreation, water transport and refuse disposal activities.
Diffuse pollution pressures in Scotland are clearly associated with the patterns of land use, with the major pressures being associated mainly with intensive arable production and in the intensive rearing of livestock. The associated problems are with phosphate (P compounds), nitrate (an N compound), suspended solids (essentially soil), pesticides, erosion/poaching of ground and faecal indicator organisms ( FIOs). This pattern of land use clearly reflects the farming/land management practices and associated inputs, as well as climate.
At a national level the sources of pollutants from agriculture, forestry, urban run-off, roads, septic tanks and sewage discharges have been estimated. Agriculture clearly dominates the losses of N, P and soils, contributing 74%, 52% and 88% of the sectors' load respectively. Sewage discharges dominate the faecal pathogen load, but with agriculture making a significant 23% contribution. Forestry is a significant contributor to soil losses. Because of the sensitivity of upland nutrient-poor lochs, P losses are locally significant.
This data demonstrates the relative contribution of agriculture and forestry on a national scale. SEPA holds significant amounts of data on a range of pollutants and ecological parameters within catchments, often over significant periods of time. The river basin management planning approach will involve identification of all sources of pollution prior to the targeting of measures at a catchment scale.
SEPA's characterisation data reflects where and to what extent impacts from diffuse pollution from agriculture and forestry are felt in terms of chemical and ecological parameters. Information on the activities causing these chemical and ecological impacts in Scotland has been compiled from farm scale diffuse pollution audit work (ref Frost et al 2000) and from subsequent research e.g. D'Arcy et al 2000.
We recognise that more work needs to be done in this area, but we are keen to begin targeting measures to the highest risk activities in Scotland. Our initial assessment of this audit data has indicated that the major activities posing a risk to the water environment include excessive use of nutrients in many cases caused by not taking into account of the nutrient content of manures and slurries, the use of inappropriately trained or briefed contractors resulting in spreading of slurry in inappropriate conditions, cropping in high risk locations e.g. arable cultivation of fields that flood regularly, cultivation of slopes next to watercourses and the creation of fine seed beds, and the access of stock to watercourses.
CASE STUDY Farm Scale Diffuse Pollution Audits - A study examined six typical farm businesses in representative agricultural sectors in Scotland and identified and assessed best management practices ( BMPs). The six farms comprised a hill sheep farm, an upland stock farm, a mixed stock and arable farm, a dairy farm, a general arable farm and an intensive arable farm with vegetable production. The survey considered the following issues: the use of pesticides, fertilisers and manures, soil protection, microbial contamination, the nature of existing water margin buffers, pollution risks from farm steadings, atmospheric pollution and the abstraction of water for irrigation. A parallel survey assessed opportunities to preserve, enhance and create habitat with a view to increasing biodiversity. A cost benefit analysis of the above practices was carried out which described the environmental benefits along with a description of the savings and costs to the farmer. The full report can be viewed at http://www.sepa.org.uk/publications/technical/imp_env_man/index.htm
- A wide range of diffuse pollution pressures were observed on the six farms. However, it was found that simple and relatively cheap changes to farming practices would produce substantial improvements in diffuse pollution risk and habitat quality.
- The main issues and the devised BMPs are described below.
- Nutrient budgets showed that on all except one farm, inputs of phosphorus in fertiliser and feed greatly exceeded offtakes of phosphorus from the farm. As the soil phosphate status in all cases was adequate, this represents an opportunity for the farmer to reduce costs, to maintain yields and to benefit the environment all at once.
- On all farms, pesticide sprayers were filled on hard standings in the steading, representing a significant pollution risk. Biobeds were proposed in most cases.
- In five of the farms, run-off of surface water from the farm steading presented a pollution risk. Farm wetland systems were proposed.
- Soil erosion from a range of pressures was sufficiently severe on several farms to pose a pollution threat to surface water. In no case, however, was the erosion sufficiently severe to pose a threat to the soil itself, except in very localised areas. Soil conservation measures and buffer strips were proposed.
- Problems were created on several of the farms (particularly the dairy farm) by their specialised nature and such problems would be reduced if a more mixed farming approach was adopted. An example would be the spreading of slurry at inappropriate times of year.
This study demonstrated the importance of farm scale audits in achieving a cost-effective reduction in diffuse pollution and associated improvement in biodiversity. |
Pesticides and veterinary medicines such as sheep dip by their very nature are designed to kill insects and other pests, and as such can cause problems if due care is not taken in their handling and application. The disposal of spent sheep dip is regulated already under the Groundwater Regulations, and is thus subject to a cross-compliance requirement.
Very small quantities of a pesticide can have a significant effect on the environment. A spillage of only 1 gram of active ingredient will need to be diluted by 10 million litres of water to meet the European maximum limit for a pesticide in drinking water (0.1 parts per billion). |
SEPA will continue to refine its risk assessment data. A new monitoring programme will be underway in 2006. For diffuse pollution, monitoring needs to be more intensive and it is planned to monitor in a range of 'priority catchments' which represent a selection of land use, soil type and climatic conditions in Scotland. More details of this and the results of further characterisation will be described in the Significant Water Management Issues Report due to be published in 2007.
We accept that not all sources of diffuse pollution are covered by the approach set out in subsequent sections of this paper. However, we believe that such an approach, coupled with CAR, will tackle the most significant pressures. In the future controls may also be brought over other sectors shown to have a significant impact on the water environment.
Questions
1. Do you agree that we have accurately identified the water quality issues that need to be addressed? If not, why and what supports your view?
2. Do you consider there are other problems not identified?
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