Understanding the impact of farming on aquatic ecosystems
Quantification of scale and importance of impact
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Quantification of scale and importance of impactThe WFD introduces the concept of risk-based monitoring and programmes have been established to assess the status (ecological and chemical) of all water bodies subject to significant pressures such as those arising from farming. This should lead to an improvement in the amount of information on the status of water bodies in terms of water categories (e.g. lakes, estuaries and coastal waters) and some pollutants (e.g. soil sediment and some veterinary medicines) not currently included in established and routine monitoring programmes, and on the spatial and geographical significance of any particular pressure/pollutants in terms of the water bodies affected. The following section summarises the main gaps in knowledge and the areas of further work and makes recommendations relating to quantification of the scale and importance of the impact of farming on aquatic ecosystems. Episodic or seasonal farming activities may cause significant effects that are not detected by monitoring programmes that employ infrequent spot sampling. Risk-based monitoring should therefore be applied for assessing the impact of pesticides when the risk of an effect is the greatest (e.g. during episodic or seasonal agricultural activities), and linked to the actual use of specific pesticides within catchments. This will enable a more complete and representative overview of the impact of agricultural pesticides on water bodies in England and Wales. The monitoring of sediments in water bodies should reflect their potential impact on aquatic ecosystems, in particular through siltation of fish spawning gravels. Research over recent years has revealed a widespread occurrence of male intersex fish in English rivers. This has now been linked with exposure to sewage effluents containing a number of feminising chemicals including steroids. However certain water bodies may have elevated concentrations of natural steroids arising from directly deposited animal urine and faeces or via other pathways. Some targeted worst-case monitoring has been undertaken in relation to farming sources of steroids, and these revealed some limited effects. Further monitoring surveys for intersex in roach and other potentially sensitive fish species should be undertaken 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. The monitoring of nitrate loadings and studies of nutrient loadings has concentrated largely on the North Sea area where loadings are thought to be largest; therefore efforts should be made to provide a more consistent coverage around UK waters. A specific routine monitoring programme should be considered for monitoring the impact of farming on a few selected representative catchments that are largely free from the effects of other pressures and which would be intensively monitored. This type of monitoring could build on the experience gained through the monitoring proposed to assess the effectiveness and outcomes of England Catchment Sensitive Farming Delivery Initiative in the 40 priority catchments.182 The monitoring programme would also provide further valuable data and information for the calibration of models that could be applied more generally. A less intensive way of monitoring the impact of agriculture (for early warning information or for general progress) would be to select those water bodies subject primarily to agricultural pressures and which are included in the EA’s operational monitoring network (Note: It may not be necessary to monitor all water bodies at risk or below good status because the WFD allows similar water bodies to be grouped and a sub-set of the group to be representatively monitored). There is a need to start undertaking larger and more comprehensive, perhaps catchment-based, projects that deal with a range of pollutants and impacts. For example, it seems that the current knowledge is not sufficient to give clear advice to decision makers on how to deal with complex impacts of combined pressures across different spatial and temporal scales183. A key issue is the influence of scales when studying ecological processes. For example, there is evidence that human actions at the landscape scale are a significant threat to the ecological integrity of river ecosystems, impacting habitat, water quality, and the biota via numerous and complex pathways184. It is also difficult to distinguish between the influence of the local riparian zone, upstream riparian zone, basin or sub-basin conditions and land use when studying causes for ecological degradation at a single site.185 Large-scale analysis comparing relationships through different scales are therefore required. This would require the study of pressure-impact relationships in geographically homogeneous areas with respect of natural factors controlling aquatic ecosystems, and to identify the relative influence of human and natural drivers on ecosystem responses. For all pollutants the assessment of the effectiveness of mitigation of control measures needs to be done regularly and over a long time scale as biological improvements may not be seen until long after the source of the pollutant has been controlled. Download 432.61 Kb. Share with your friends:
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