Understanding the impact of farming on aquatic ecosystems
Knowledge of activities, pathways, processes, source apportionment and impacts
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Knowledge of activities, pathways, processes, source apportionment and impactsThe following Section summarises the main gaps in knowledge and the areas of further work relating to activities, pathways, processes, source apportionment and impacts. Specific recommendations are given as number paragraphs. 1. The processes of loss and the pathways to watercourses are reasonably well understood for soluble nutrients such as nitrate. However there is less specific information about the details of transport within any given catchment for less soluble pollutants and pollutants that are accumulated on soil. This lack of information is in two main areas. For hydrophobic contaminants that are predominantly associated with sediment there is a need for a better understanding of sediment transport and behaviour and of the processes by which absorbed substances might be released. For less hydrophobic substances there is a need to obtain greater understanding of the processes that control adsorption to suspended particulate matter in order that the mechanisms of pollutant transport can be made clearer. 2. The quantities and proportion of some pollutants originating from agricultural activities that become associated with sediment needs to be established. There is relatively good information for phosphorous where it is estimated that approximately 60% of phosphorous is lost via absorption to sediments. The case for other pollutants particularly organic material and pathogens is less well quantified and understood. 3. More information is needed on the quantities of ammonia contained in fertilisers that is being converted to nitrates/nitrites prior to being leached from soils and how much is actually lost as ammonia. 4. Current monitoring of sources and pathways concentrates on those which are most evident and easy to measure rather than smaller incidences which can have a cumulative effect such as those relating to sediment. Monitoring should be extended to capture the smaller processes and enable an assessment of the importance of such processes. 5. It is known that certain types of farming practices leave soils more susceptible to erosion than others. Risk maps in terms of loss of sediment to water bodies could be drawn up at a national scale in order to document these risks and in order to better direct mitigation measures. 6. In particular for pathogens, research is required into pathways (e.g. transport in soils via vertical mechanisms and by-pass flow), pathogen survival and mitigation. This type of information should improve the performance of current pathway models. 7. Better quantification is needed on losses of organic material from diffuse sources such as yard washings and loss from manures applied as fertilisers. Moreover, soil sediment and some types of organic material are often not treated as separate pollutants and needs to be addressed because of their very different properties. 8. There is a lack of source apportionments for pollutants such as organic matter, soil sediment, pesticides, veterinary medicines, faecal pathogens and endocrine disrupting chemicals. There also needs be a better balance between the source-orientated approach and load-orientated approach for a better apportionment of loads and understanding of likely impacts. 9. Further research is also needed on diffuse sources of nitrates to coastal waters taking into account more recent issues such as fish farming and disposal of fish wastes. 10. The impacts of organic matter and ammonia on aquatic organisms are relatively well understood as they have been monitored for many years, in particular in relation to the impact of discharges from sewage treatment works and disposal of sewage sludge, and to assess the general quality of rivers. Research has also been undertaken on the potential impacts of sediment on aquatic organisms particular in terms of the silting of fish breeding gravels and their impact on dissolved oxygen concentrations in the water column. The relative scale of the potential impact of sediment has also been highlighted by the WFD Article 5 risk assessments. 11. The impact of nitrate on aquatic organisms has generally been considered in terms of the indirect effects of eutrophication e.g. increased turbidity, oxygen demand arising from the degradation of organic material etc. There is some evidence that some organisms may also be sensitive to nitrate at concentrations not uncommon in freshwaters. Also nitrate and ammonia contribute to the acidification of water bodies, particularly upland water bodies with low acid neutralising capacity. There are well known effects on aquatic organisms arising from decreases in pH. There is also a lack of information and data on some veterinary medicines that precludes detailed assessment of their potential impact on aquatic organisms. 12. It is recommended that the potential toxicity of nitrate to freshwater organisms is further investigated, and that the contribution of nitrate arising from agriculture to acidification is further quantified. 13. There is a poor understanding of the relative importance of water and sediment sources of phosphorus for vegetation (macrophyte) growth in both rivers and lakes181. Thus the impact of particulate sources of phosphorus or sediment-bound phosphorus on important diagnostic ecological communities is less well understood, but it is likely that even in faster flowing river systems phosphorus will impact on ecological status. Further research on these aspects is therefore required. 14. In terms of the impact of veterinary medicines on aquatic ecology there is a need for a more detailed assessment of the potential impacts of veterinary medicines on soil in general and in particular investigations into the fate and effects of parasiticides in sediment, and how that might affect potential pathways to water bodies. There is also a lack of information and data on some compounds that precludes detailed assessment of their potential impact on aquatic organisms. In particular, there is a need to monitor for the presence of these compounds in groundwater. 15. Research over recent years has revealed the occurrence of male intersex fish in English rivers mainly in relation to exposure to sewage effluents containing a number of feminising chemicals including steroids but also, to a more limited extent, in relation to livestock farms as a potential source of steroid hormones. It is recommended that surveys for intersex in roach and other potentially sensitive fish species are extended to include a representative range of water body types and levels of farming and other pressures to determine the geographic extent of intersex and whether farming is potentially a significant source (compared to sewage effluents for example). In addition, further work is required to understand the implications of endocrine disruption (from all sources) on the structure and functioning of fish populations as a whole, and on other taxonomic groups (such as invertebrates) for which there is very limited information. 16. The WFD requires that certain quality elements are used to monitor and assess the ecological chemical status of water bodies. For most Member States the scope of the elements required went beyond their existing national monitoring programmes and assessment schemes. There has been a concerted effort at European and national levels to identify and fill these gaps. For example, the European WFD Common Implementation Strategy Working Groups and the UK Technical Advisory Group have identified gaps in knowledge and the need for further development. Some of those relevant to the monitoring and assessment of the impact of agriculture are listed below: these are likely to be subject of further research for European (under Framework 6 and 7 for example) organisations as well as UK regulators. There is a general lack of knowledge on the combined effects on ecology of mixtures of toxic substances in water that may individually be below EQSs concentrations. There is also a general lack of knowledge on the responses of aquatic ecosystems to combined pressures. The relationships between nutrient concentrations and phytoplankton growth in rivers are not well known. The concentration of nutrients may not be the only factor triggering algal blooms. Hence the respective effects of nitrate and phosphorus, and their ratios and different forms on phytoplankton biomass and assemblages need further investigation in large rivers. Further research is needed to investigate the occurrence of algal blooms in coastal waters specifically in areas adjacent to agricultural catchments, and the extent to which the nitrogen:phosphorus ratio and also silicate control algal blooms with an assessment of the importance of nitrogen. This would need to be undertaken over a long time scale in order to capture seasonal fluctuations and underlying trends in algal blooms. There is a lack of information on the responses of macrophytes to nutrient conditions in general and in particular quantification of relationships that distinguish the effects of nutrients from the effects of other variables, the response of macrophytes to nutrients in sediments, and lack of robust quantitative relationships between water quality and macrophytes in coastal waters. There is an absence of quantitative relationships between phytobenthos and nutrients. There is lack of knowledge on the ecological impact of nitrogen conditions on some lakes and rivers, particularly their potential to limit primary production. The responses to, and functional relationships between, phytoplankton, macrophytes and benthic invertebrates in rivers and organic pollution from urban and agricultural run-off are not well known. The impacts of sediments in lakes need to be better understood and differentiated from natural infilling processes. There is potentially scope to improve the responsiveness of certain biological indicators by modifying the assessment procedure and focussing on particular sensitive elements of a given index. Download 432.61 Kb. Share with your friends:
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