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Programme d’Etude et de Recherche 2009-2012 : Mise au point d’un indice de bio-indication de la qualité de l’eau des cours d’eau Antillais à partir des diatomées : l’IDA. Rapport Final (Version Finale du 14/10/2013)

Abstract : In the specific biogeographical context of the french Caribbean, which includes many species of tropical diatoms unknown in continental France, no pre-existing diatom-based method of bio-indication is proven reliable for the diagnosis of ecological status in rivers. In order to implement the WFD, which should also apply to the French overseas departments, Martinique and Guadeloupe hydrosystem management services (Water Offices , DEALs) supported by ONEMA launched in 2009 a research - transfer program of 3 to 4 years in the aim to : 1) track and identify diatom flora of each island; 2) study their ecology ;3) implement a specific diatomic index that can then be used to diagnose the ecological status in the context of routine monitoring networks. This program taken in charge by the ASCONIT - IRSTEA consortium prospected a total of 110 stations on the two islands during five seasonal sampling campaigns, and performed 483 biofilm samples representative of each site, linked with more than thirty abiotic descriptors (including 27 physico-chemical parameters) at the same date. Among them, 475 complete surveys were fully exploited . 470 different diatom taxa have been identified and taken into account. An exploratory analysis using a neural unsupervised technique (SOM) identified a bio-typology made of natural assemblages on the one hand, and those organized by the main types of alterations encountered in the Caribbean on the other one. Classical multivariate techniques (PCA, CCA…) were used to explain the structure of abiotic gradients contained in the dataset and their correspondence with the species distribution and assemblage composition. IDA (Indice Diatomique des Antilles) was built on an “anthropogenic composite integrative gradient” made of nine abiotic variables significantly influenced by human pressures. After locating the broad natural variation on the natural reference sites, the composite gradient of human impact has been divided into five abiotic quality classes and then used to decline ecological profiles of the constitutive species. After thresholding species on the base of their occurrence and relative abundance, 179 taxa were judged as sufficiently distributed to wear a calculation of environmental quality profile and to be involved in the calculation of the index. 49 of them are considered as “Alert Taxa” and contribute to the decrease of the index notes. As part of this final report, which incorporated the methodological changes discussed at the final steering committee of the initial study, two large natural ensembles were identified to set-up two grids based on Equivallent Quality Ratios, used as a basis for the evaluation of the Ecological Status: 1) a common little mineralized volcanic zone regrouping the volcanic portions of the two islands, on which the NINC species is considered as an alert taxon; and 2) a zone of highly mineralized plains corresponding to the “zone des Mornes” of Martinique, which does not take into account NINC as an “Alert Taxon”. The evaluation system tested here gives relatively satisfactory overall results, but seems to be perfectible on some particular sites. It will be consolidated at a later stage with the acquisition of additional data acquired on targeted sites, which will aim in particular to better identify the ecological profile of NINC and the final modalities of its mobilization in the calculation of the IDA.
Mots-clés : DOM ANTILLES
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A. Eulin, E. Lefrançois, Sébastien Boutry, Juliette Tison-Rosebery, Michel Coste, et al.. Programme d’Etude et de Recherche 2009-2012 : Mise au point d’un indice de bio-indication de la qualité de l’eau des cours d’eau Antillais à partir des diatomées : l’IDA. Rapport Final (Version Finale du 14/10/2013). [Rapport de recherche] irstea. 2013, pp.266. ⟨hal-02605884⟩

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