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Tools to assess the ecological status of surface waters in overseas territories

Leading up to the second WFD cycle (2016-2021), a major R&D effort has been made to equip overseas territories with suitable bioassessment tools for their aquatic environments. The tools are indispensable for assessing the ecological status of water.

The European water framework directive (WFD) requires that the Member States set up bioassessment tools to determine the ecological status of aquatic environments. Each tool is based on a biological community, e.g. microscopic algae, aquatic macrophytes, benthic invertebrates and fish. In continental France, the development of most of these complex tools was terminated in 2012, following years of intense work by the scientific community and managers of aquatic environments.

WFD requirements apply without restriction and according to the same timetable to the French overseas territories whose aquatic environments are home to very specific and often highly diversified fauna and flora. Amazonian rivers and coral reefs constitute fantastic biodiversity reservoirs. The development of suitable bioassessment tools constituted a true scientific challenge, due notably to a lack of knowledge on the existing pressures and species. It was carried out in a short number of years by the local Water offices in conjunction with national research institutes (Irstea, IRD, CNRS, etc.) and with technical and financial support from Onema.

For example, on Réunion island, the programme launched in 2008 produced in 2012 a set of WFD-compliant bioassessment tools that are now being validated by aquatic-environment managers. One tool based on diatoms (microscopic algae) informs on the general physical-chemical quality of the environment, whereas two others using fish and benthic macroinvertebrates are sensitive to the physical degradation of habitats. Irstea, with technical coordination by Onema, is currently studying whether a tool using macrophytes would be of use, given the highly irregular hydrological regimes of overseas rivers. This study is being carried out in all the French overseas territories.

Some 13 000 kilometres from Réunion, two bioassessment tools were developed for both Martinique and Guadeloupe, whose ecosystems are fairly similar. Intended for rivers, the first tool is based on diatoms and the second on macroinvertebrates. The two tools are now being transferred to the technicians in the field and should be ready for the second WFD cycle. Bioassessment tools are also available for certain types of water bodies in Guiana, but they must be improved in view of the third WFD cycle. Finally, a research partnership between INRA and Onema was started in 2012 to develop bioassessment tools tailored specifically for the rivers of Mayotte, another overseas territory. These tools will call extensively on innovative methods including experimental DNA and genetic techniques.


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