Background

Aquatic invertebrate surveys are typically carried out to assess the water quality of a particular waterbody, either as a one off assessment or ongoing surveys over a period of several years to monitor the effect of land and water use from mining, agricultural or recreational activities. They may also be carried out for monitoring the effects of mitigation or simply in assessing the aquatic invertebrate diversity of a site, particularly as part of a planning application affecting a watercourse.

Timing

The optimal period for aquatic invertebrate surveys is May to August. Surveys can be carried out in late March to April and September to mid-November, but many species will not be present at this time so additional surveys within the optimal period may be required to provide a complete picture of the invertebrate species present.

Methodology

EMEC Ecology is able to undertake a range of freshwater aquatic invertebrate surveys including the following:

Water quality monitoring using macroinvertebrates as biological indicators and the Biological Monitoring Working Party (BMWP) procedures to determine the quality of a watercourse, indicative of pollutant levels. This industry standard method relies on the principle that different aquatic invertebrates have different tolerances to pollutants and water oxygen concentrations. In addition to the BMWP score, the Average Score Per Taxon (ASPT) score is calculated from the collected samples. The ASPT equals the average of the tolerance scores of all macroinvertebrate families found, and ranges from 0 to 10. The main difference between both indices is that ASPT does not depend on the family richness.

The BMWP and ASPT values gathered from survey work carried out by EMEC Ecology can be used in reports relating to the Water Framework Directive (WFD). The WFD is a European Union (EU) directive that has been incorporated into English and Welsh law. It aims to enhance and prevent deterioration of aquatic ecosystems, reduce water pollution, promote the sustainable use of water and ensure progressive reduction of groundwater pollution.

In addition to BMWP and ASPT, EMEC Ecology has experience of using several other statistical techniques, including the Extended Trent Biotic Index (ETBI), and Community Conservation Index (CCI), as well as statistical techniques such as the Shannon Weiner diversity index, Whalley, Hawkes Paisley, Trigg (WHPT) index, Lotic Invertebrate Index (LIFE), and Proportion of Sediment Sensitive Invertebrates (PSI) index as appropriate and as required by our clients.

Surveys to discover species composition in order ot ascertain the invertebrate "richness" of a site or the effect of management of watercourses on the invertebrates found therein can also be undertaken. We can carry these out before and after any known changes to watercourses to determine the impact of structural and vegetation changes on species composition.

All EMEC Ecology aquatic invertebrate surveys are carried out according to standard Environment Agency and Natural England procedures, therefore making them suitable for inclusion in Water Framework Directive (WFD) reports.

Typically, as part of an aquatic invertebrate survey EMEC Ecology will use probes to measure water chemistry indices including pH, dissolved oxygen concentration and electrical conductivity. These measurements give a useful context to the main survey in assessing water quality.

Following the Survey

Following an aquatic survey, extensive mitigation advice on freshwater systems can be given, not only including in improving the invertebrate diversity of the site, but also reducing the impacts of pollution and improving the 'health' and appearance of the water.