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Implication and works of Cemagref diatom team in REBECCA / WP4 / Task 3: Nutrients causing eutrophication

Abstract : This meeting organized by Cemagref in Lyon (FR ) is a Joint WP4 -WP6 Rebecca / Meeting. The present t alk, given by Cemagref, makes the point of the work done on the French diatom dataset since the beginning of the project. The beginning of the talk describes methodological aspects concerning data improvement and data processing before beginning the step of data mining. Then a first scientific purpose of our work was to make the part between the effects of the natural (abiotic) variation on diatom communities and the effect directly linked to anthropogenic disturbance. For that, we proceeded a diatom community biotypology , then linked the obtained clusters to a set of structuring abiotic variables. On the French territory,this allowed to identify 11 different biotypes, 5 of them being mostly driven by a set of natural abiotic conditions, providing 5 "Reference " natural biotypes found in natural specific environments) and 6 other biotypes impacted by different kind and intensities of anthopogenic alteration. Another orientation of the work addressed the reduction of species number, aiming at a simplification of a given national dataset without loosing structuring information. With the help of the GSI, a structuring index set-up in our research team, in our national situation, we could strongly reduce the number of species (from 941 to 353) without significant loss of ecological information. Working on 941 / versus 353 species with the INDVAL provided the same lists of structuring species by biotype (natural / altered by anthropogenic impact). On the basis of a set of abiotic structuring parameters, the obtained clusters have been linked with the same specific abiotic conditions. The obtained typology defined a natural framework for France, composed of 5 natural biotypes that we could link with a pre-existing abiotic (i.e. HER1) framework set-up for France. Then was presented the progress done by France concerning the setting-up of a national assessment system based on IPS, allowing to evaluate the ecological status of sites in a way that follows the WFD guidelines. 234 true reference sites have been selected, made of 5 "reference " natural biotypes. This natural framework then allowed to set-up a national assessment system (not presented here). The last part of the talk concerns the expression of relationships between nutrients and diatom index notes (IPS). Global relations at the French territory scale provide weak to stronger relations, depending on the nutrient. Despite reduction of the dataset, these relationships improve on a selection of more homogenous natural types of rivers. It is also the case if we select a range of elevations (elevation and slope conditioning intensification of human uses and practices). Finally, combination of different species of nutrients gave some improved relationships. This is easy to understand, IPS being based on a composite gradient of 7 different abiotic parameters under strong influence of anthropisation. Promising results were obtained in expressing the log-transformed nutrients load and creating a composite variable made of a product (N*P values).
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Submitted on : Saturday, May 16, 2020 - 7:38:50 PM
Last modification on : Thursday, June 3, 2021 - 5:34:03 PM

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  • HAL Id : hal-02610328, version 1
  • IRSTEA : PUB00064452

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Juliette Tison-Rosebery, Y.S. Park, Michel Coste, François Delmas. Implication and works of Cemagref diatom team in REBECCA / WP4 / Task 3: Nutrients causing eutrophication. 6th FP REBECCA Project - WP4 & WP6 Activity Groups, Cemagref Meeting, Apr 2006, Lyon, France. pp.20. ⟨hal-02610328⟩

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