Understanding the impact of farming on aquatic ecosystems
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- Trends in agricultural production and potential impacts on aquatic ecosystems
- Impact of pollutants on aquatic ecosystems
ApproachThe report collates and assimilates data and information from sources including: Defra research projects (searched via Defra http://randd.defra.gov.uk/), Environment Agency technical reports and science reports, UKTAG reports and guidance notes (searched via http://www.wfduk.org/) and WFD Article 5 risk assessment reports and technical methods (available at http://www.environment-agency.gov.uk/subjects/waterquality/955573/). In addition, a full CSA (http://www.csa.com/csaillumina/login.php) search was conducted for relevant journal articles and scientific reports using three keyword searches: (1) to search for information on the sources and exposure pathways of pollutants we used the following terms: agriculture, pollution, water quality, source, transport, pathway, diffuse pollution, run-off, agriculture, UK; (2) to search for information on the impact of these pollutants on aquatic ecosystems we used the following terms: pollution, water quality, impact, effect, stress, ecology/ecological, species, population, community, toxicity, river, lake, estuary, coast, freshwater, marine, UK; (3) to search for information on indicators that are used to assess the extent and intensity of pollution we used the following terms: (iii) pollution, water quality, bioindicator/biological indicator, impact assessment, indicator species, index/metric, river, lake, estuary, coast, freshwater, marine, UK. A full reference list is provided in Section 6, where the availability of these documents is flagged. Trends in agricultural production and potential impacts on aquatic ecosystemsStudies have been undertaken to assess how the reform of the EU’s Common Agriculture Policy and other policies will impact on farming and water quality. Some of the main predicted changes and projections to 2015 relevant to potential impacts on aquatic ecosystems include: Overall land use will not change markedly;3 Changes in farming practices will help reduce levels of nitrate and phosphorus in surface and ground waters;4The per hectare applications of fertiliser and sprays unlikely to change markedly;5 Extensification of grassland utilisation is likely to lead to reduced fertiliser applications;6 Marked reduction in livestock numbers;7 Fewer larger herds of dairy cows – disappearance of mid-sized herds, focus of production will be in the lowlands. Pressures of dairying will be concentrated in specific areas (more slurry to be stored). 8. In some parts of country (South West) the size of herds is already increasing;9 Reductions in livestock numbers are likely to lead to reductions in levels of veterinary medicines in water bodies in main livestock regions e.g. South West and West Midlands – though intensification of dairying in parts of these regions may see an increase in localised areas;10Fewer sheep will mean a reduction in sheep dip use;11 and Fewer cattle and sheep will reduce problems with poaching12 and potential soil erosion; Outdoor pig sector to increase to escape from measures required under IPPC Directive for installations for the intensive rearing of pigs (and poultry).13Climate change will have a significant effect on agriculture and potentially its impact on aquatic ecosystems. Defra summarises the direct threats from climate change as prolonged and more frequent droughts; changes in rainfall distribution; more storms and other extreme events; rising sea levels; increased and changing pest loads; increased risk of heat stress in livestock farming; and, possible changes in soil water balance.14 Increasing temperatures and hence growing seasons may also lead to new crops being grown. Other predicted impacts include: increased/change in range of native/alien pest and disease problems15 (leading to the use of more or different pesticides); increased use of irrigation16 (increased abstractions in some catchments); increased soil erosion (increased sediment loads to water bodies); changed poaching/water logging risk in some areas (changes in pollutants pathways and increased sediment load). Changes in intensity and seasonality of rainfall and increased temperatures may change the fate and behaviour (and hence impact) of pesticides though the overall effect may be very variable and difficult to predict.17 The likely scale of the changes to agriculture that would be required to achieve good ecological status (GES) for the WFD in terms of nitrate and phosphorus has been modelled.18 The results predict that the achievement of GES would require substantial changes in agricultural land use and management. These might include identification of high risk areas where the risk of nutrient export is high, controls on fertiliser use and livestock densities, and taking sensitive areas out of production. For example, total nitrogen fertiliser usage and livestock numbers have declined in recent years and could be expected to reduce agriculture’s contribution to water pollution.19 However, other changes, such as the continuing trend towards intensification, are likely to counteract this to some extent. A more detailed description of sources and pathways of pollutants, and strategies to tackle agricultural water pollution, is given in Annex A to this report. Impact of pollutants on aquatic ecosystemsThis section reviews, for each of the ten pollutant categories listed in section 1.3, the key sources and pathways, the magnitude of source and exposure pressure (including an assessment of the proportional contribution from farming), the potential impact on aquatic ecosystems, and the current extent and intensity of impact. In assessing the extent and intensity of the impact of farming on aquatic ecosystems, the report draws heavily on the results of the Environment Agency’s (EA) WFD Article 5 risk assessments, which identify those water bodies at risk of failing to achieve the WFD objectives, such as the achievement of good ecological and chemical status due to different categories of pressure. The risk assessments give an indication of the potential impact of agriculture on the ecological status of water bodies. However, water bodies were often identified as being at risk from more than one pressure making it difficult to apportion the impact arising from agriculture from that arising from other activities and sectors. Also some of the risk assessments were based on modelling rather than on direct evidence of ‘impact’ on ecological status. Therefore, even though the risk assessments identify the potential scale of the impact of agriculture on ecological status, the actual impact may not have been fully quantified. The UK Technical Advisory Group on the Water Framework Directive (UKTAG) has proposed environmental standards for the implementation of the WFD and has assessed the implications of applying them to existing monitoring data in terms of achievement of good ecological status.20,21 These results are also referred to in the text below as appropriate. The first full classification of ecological status of water bodies will be available in December 2008 when draft River Basin Management Plans will be published. Download 432.61 Kb. Share with your friends:
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