Understanding the impact of farming on aquatic ecosystems
Species/biological quality elements indicative of the effects/impacts of farming
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- Monitoring under the Water Framework Directive
Species/biological quality elements indicative of the effects/impacts of farmingThe pressures arising from farming and the subsequent impacts have been described in detail in Section 2. The species/biological quality elements indicative of these pressures and impacts can be summarised as follows: Nutrient enrichment The most sensitive indicators of the impact of the nutrients nitrate and phosphate on an aquatic ecosystem are considered to be combinations of phytoplankton, phytobenthos and macrophytes in rivers and lakes and phytoplankton, macroalgae and angiosperms in transitional and coastal waters.167,168 Organic material enrichment The available evidence indicates that benthic invertebrates are the most sensitive indicators of organic material enrichment (e.g. elevated concentrations of BOD, ammonia and suspended solids) in all receiving water types.169 Acidification Acidification of freshwaters can result in a complete loss of fish species (the early life stages of trout and salmon are particularly sensitive170) and changes in community structure and biodiversity in general, particularly in terms of benthic invertebrates (e.g. reduction in sensitive species taxa such as Ephemeroptera, Crustacean and Mollusca) and aquatic plants (e.g. diatoms)171. Pollutants The impact of pollutants (e.g. pesticides, ammonia, veterinary medicines, endocrine disrupting chemicals, heavy metals, oil) on different elements of an aquatic ecosystem will be dependent on the mode of action of the substance(s) involved and, therefore, the taxonomic group(s) which are most susceptible to the substance at typical environmental concentrations. In the case of herbicides, phytoplankton, phytobenthos, macrophytes and macroalgae would be expected to be the taxonomic groups most affected by exposure in the receiving water. For insecticides and molluscicides, crustaceans and molluscs would be expected to be those most likely to be affected by exposure to these substances at typical environmental concentrations.172Fish are the taxonomic group most sensitive to ammonia. Habitat alteration Habitat alteration resulting from sediment accumulation following soil erosion can potentially have direct or indirect effects on all the biological quality elements resident in a water body. For example, high suspended solids concentrations can affect the feeding and health of individual species either indirectly through increased turbidity of the water (thereby inhibiting phytoplankton, phytobenthos, macrophyte, macroalgal or angiosperm growth) or directly through clogging of gills of invertebrates and fish. Siltation is a problem both with regard to access to suitable substrate – for example, for the establishment of the freshwater pearl mussel (Margaritifera margaritifera) and water crowfoot (Ranunculus spp.) plant communities – and with regard to egg and fry survival in Atlantic salmon (Salmon salar), lamprey (Lampetra and Petromyzon spp.) and bullhead (Cottus gobio) populations.173 Monitoring under the Water Framework DirectiveThe WFD defines ecological status in terms of the status of biological, physicochemical and hydromorphological quality elements reflecting the structure and functioning of aquatic ecosystems. Chemical status relates to compliance with European EQSs established for a Priority List of substances and for substances covered in other EU legislation. Surveillance monitoring for the WFD is required for parameters indicative of all biological, hydromorphological and general physicochemical quality elements, Priority List substances if discharged in the River Basin District and other pollutants if discharged in significant quantities. Operational monitoring is required for parameters indicative of those biological and hydromorphological quality elements most sensitive to the pressures to which the water body is subject (i.e. those priority substances discharged into the water body and other significant pollutants (including nutrients) that might cause failure of environmental objectives). Thus water bodies identified as being at risk from farming activities and pressures (and hence included in operational monitoring) will be monitored using parameters most indicative of that pressure. These water bodies may also be included in surveillance monitoring, in which case all quality elements will have to be monitored for. The assessment and classification of the ecological status class of a water body will be based on the monitoring results of the parameters included in surveillance and operational monitoring. In some cases obtaining a reliable assessment of the conditions of a particular biological quality element may require consideration of the monitoring results for several parameters indicative of that element. The WFD gives the minimum quality elements that should be used in the assessment and classification of the ecological status of each of the four water categories (rivers, lakes, transitional and coastal waters). The results for several parameters or groups of parameters, each sensitive to a different pressure or set of pressures, may be used in estimating the condition of the biological quality element. Multi-metric indices may also be derived from measurement of individual parameters to assess whether the quality element has been affected by the pressures to which the water body is subject. As an example, the indicative parameters (metrics) based on measurements of composition and abundance of benthic invertebrates could include: 174 presence or absence of particular species or groups of species; overall richness or richness of particular taxonomic groups; relative number of taxa in particular taxonomic groups; abundance of particular species or groups of species; relative abundance of particular species or groups of species; overall diversity, or diversity within particular taxonomic groups; taxa could be selected and/or grouped by known sensitivity/tolerance, feeding type, habitat preferences, etc. The EA will be responsible for undertaking the monitoring required for the WFD in England and Wales. To that end, the UKTAG has recommended appropriate quality elements for the monitoring of the impacts of the pressures listed in Table 1. As has been pointed out, these pressures are associated with, but are not exclusive to, farming. The recommended quality elements vary depending on the nature of the pressure and the receiving water. The process of determining which parameters have the best correlation with particular pressures and impacts is underway. It should be recognised that not all of the elements which are relevant to farming-related pressures are being fully addressed under the UK research programme. Phytoplankton in rivers is not being considered since the turnover in the majority of UK rivers is too high to support a phytoplankton community and this element has not historically been widely monitored. This quality element will be monitored on a risk-based approach in those rivers where phytoplankton may be important. Table 1 Biological quality elements likely to be used to assess pressures relevant to the impact of farming activities
Notes: Elements in bold are likely to have the strongest sensitivity to the pressure Elements in brackets require further work as more data is acquired Elements underlined in italics recommended by CIS WG2.7175 Source: UKTAG 2005176 Details of the indicative metrics and methods proposed for the assessment and classification of water bodies in England and Wales are given in Annex B to this report. The aim will be to have indicators, metrics and methods that are responsive and suitably sensitive to changes in the pressures/effects being monitored. At present a number of ecological indicators show statistical significant relationships with pressures which are relevant to farming-related activities. However, in many instances there is a high degree of variability associated with the relationships which limits their wide-scale application. It has been reported that the variation between relationships for indicators of biological quality elements and specific pressures was larger when they were derived from European wide datasets containing information from many different sites. The quality of the relationships was improved by creating sub-datasets for geographical regions and types of water bodies177. Relationships may, therefore, have to be water body type-specific rather than generic. Detecting the impact of many of the farming related pollutants/pressure will rely on the selected quality element being sensitive enough to the pressure, for example, siltation and endocrine disrupting effects would expected to be detected by changes in fish populations. Statistically valid changes in the metric/indicators must also be detectable over and above all sources of variability (natural and anthropogenic) in water bodies. Using this type of statistical assessment, it should be possible to determine the smallest change detectable and to assess how that relates to changes in the pressure and impact and the degree of early warning obtainable. Depending on what is an acceptable or desirable level of early warning, some WFD methods may not be suitable for providing an early warning of impacts from some farming activities. For example, intersex in fish would probably have to become very prevalent before it would be detected by changes in the fish population metrics ‘composition, abundance, sensitive species and age structure’ that will be used in the classification tools for the WFD. [Note: The relationship between intersex in fish and fish populations and community structure has been identified as a gap in current knowledge (section 2.9)]. Once the chemical(s) responsible for inducing intersex had been determined then it would probably be subject to an EQS that would be aimed at reducing the risk of intersex occurring. In short, more sensitive and targeted indicators and methods may be required if early warning of some farming induced impacts were to be required before they were detectable by a deterioration of ecological status as defined by the WFD. Download 432.61 Kb. Share with your friends:
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