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Bioindication d'état et de fonctionnement en plan d'eau : Utilisation des traits morpho-fonctionnels du phytoplancton pour définir des métriques de diagnostic Rapport final

Abstract : This work is in line with the development of a multi-metric index for the assessment of the ecological status of water bodies with respect to the phytoplankton compartment in water. Thus, it is linked to the IPLAC index. In the end, it aims to complete its evaluation with so-called diagnostic metrics to account for other pressures and elements of biodiversity. For this we used a large-scale morpho-functional approach (national territory) of phytoplankton communities, based on the definition and use of 84 morpho-functional traits of phytoplankton, covering all taxonomic groups, as a descriptor of communities. In aquatic ecosystems, relationships and interactions between phytoplankton communities and environmental variables are often quite complex. So, different statistical and numerical tools such as Random Forest (RF) in regression and classification mode, Partial Dependent Plots (PDPs) have been tested to take into account this complexity. RF methods have shown that depth of waterbody and altitude are important factors. This led to the creation, by the K-means method, of four typological groups, based on these criteria, to subtract the effect. Subsequently, various tests of direct correlations, on each of the typological groups, were carried out but results are rather disappointing. In a second step, RF models in regression mode then classification mode were used. However, their uses drive us away from the DCE compatibility because they have not allowed us to derive relationships and metrics relating to a trait or combination of exploitable traits. Lastly, an approach using PDPs has been implemented. Of the 84 constructed traits, 21 are highlighted by the result analyses with direct or indirect links to physico-chemical water parameters. These include traits: life form (solitary, filamentous), motility, presence of protuberances, pseudo-vacuoles or the presence of Chlorophyceae or Euglenophyceae. The dissolved organic carbon, the total suspended solids, the nitrates or the transparency measured by Secchi disk are the physicochemical parameters that have relations with morpho-functional traits. The use of PDPs allows knowing the variation direction of the existing relationship between the trait and the physicochemical parameters. On the other hand, threshold values do not depend on the created typological groups. This work should allow the definition of new trait-based diagnostic metrics for DOC and nitrate gradients. This will refine the understanding of the impact of anthropogenic pressures on lake ecosystems.
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https://hal.inrae.fr/hal-02608848
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Submitted on : Saturday, May 16, 2020 - 5:03:44 PM
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Christophe Laplace-Treyture, J. Derot, Soizic Morin, Juliette Tison-Rosebery. Bioindication d'état et de fonctionnement en plan d'eau : Utilisation des traits morpho-fonctionnels du phytoplancton pour définir des métriques de diagnostic Rapport final. [Rapport de recherche] Irstea. 2019, pp.79. ⟨hal-02608848⟩

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