Guyane QUES

CNR-IRSA activities related to INHABIT

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Home Main projects Guyane QUES

Guyane QUES

The QUES-Guyane project (QUalité des Eaux continentales de Surface de Guyane), was coordinated by the 'INSTITUT DE RECHERCHE POUR LE DEVELOPPEMENT' - IRD, Cayenne, Guyane, and was focused on research activities in the field of fluvial ecosystem functioning in relation to Water Framework Directive implementation (WFD -2000/60/EC). More in detail the collaboration was dedicated to the elaboration of available data from French Guyanese large rivers in order to elaborate a multimetric index for the evaluation of ecological status on the basis of benthic aquatic invertebrates.
The main objective is to outline a procedure to define a system for the evaluation of ecological status on the basis of river invertebrates. In particular, the focus was addressed on:

  • collation of available data (provided by different Guyanese Institutions) and organization of the data in a access based database to be able to prepare matrices for data elaboration;
  • physico-chemical characterization of river sites;
  • identification of the main gradients described by environmental variables and describing/affecting invertebrate communities;
  • providing a tentative river typology for Guyana rivers, which is sound for benthic communities and respects WFD requirements;
  • selection of key indicator taxa to be used in the assessment of ecological status;
  • selection of candidate metrics and proposal of a multimetric index for ecological status classification based on aquatic invertebrates;
  • deriving ecological boundaries - and outline of the procedure - and comparison with those agreed in Europe within the intercalibration exercise;
  • provide a preliminary classification of river sites/samples.

Results of the project, for the river benthic component, are hereafter summarized:

  • A proposal for defining river types, which are relevant for benthic communities, has been outlined. The resulting typology is in line with WFD requirements and is mainly based on stream size and pH. 4 different river types, checked by crossing abiotic and biotic information were thus identified: acid mid-sized (aM), acid large (aL); neutral mid-sized (nM), neutral large (nL) large-seized. The acid category is applied when pH< 5.8. Refinements can be expected, especially by adding further parameters that can allow a better discrimination of sites, diminishing the possible natural variability. In the analyzed data it was moreover clear that rivers with tidal influence represent a differ group.
  • Reference conditions do not seem to represent a problem for WFD application in Guyane. In fact, the area is characterized by generally low anthropogenic pressures, mostly affecting the coastal areas.
  • It was possible to identify a core set of metrics to be included in a multimetric index (GAINi) for the definition of ecological status based on aquatic invertebrates. These metrics are considered to be robust enough in relation to the available literature and knowledge on hand. The selected metrics were based on family level.
  • The proposed multimetric index (GAINi) demonstrated its ability to discriminate reference sites from sites affected by different kinds of pressure. In addition, it was concluded that the discriminatory power of the invertebrate-derived information improves when the SMEG index (based on Ephemeroptera identified at genus level) is combined with the GAIN index, especially for the detection of the impact on the aquatic community linked to gold mining activities.
  • The sites classification showed that most of the investigated sites are classified in ecological status better than Moderate, suggesting that reaching WFD environmental objectives may not be a substantial problem for Guyane – with the due exceptions related to more local situations. This is also true when considering the proposed class boundaries, that are in line with the presently adopted European boundaries.
  • Finally, mention has to be done of biological interactions - especially  predation by fishes – that can be potential very high in Guyane rivers. It is reasonable to affirm that assessment systems based on aquatic invertebrates should be designed to cope with different levels of biological ‘pressures’, so that indices values are not related to, or are corrected for, important interactions with other taxa, particularly those belonging to a higher trophic level or acting as keystone species.

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