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Evaluation diatomique des Très Grands Cours d'Eau (TGCE) de France et intercalibration européenne : Rapport Final

Abstract : The Water Framework Directive implementation requires a regular ecological status assessment of water bodies within the framework of 6-year management plans. The objective is to avoid the degradation of the ecological status or to restore the Good Ecological State to the deadline foreseen in the SDAGE, ie no later than the end of 2027. In that purpose, a first national "Evaluation Circular" was published in July 2005. Since then, this official text has already been subjected to several updates, the previous one (i.e. Evaluation Decree of 27 July 2015) still having force of application on most types of French rivers. However, the very large rivers at the meaning of the WFD (catchment area exceeding 10 000 km2 at the observation station) were not yet covered by a coherent national assessment system, because of certain specific difficulties encountered in our country and at the European level (in particular, complete absence of true references on such hydrosystems, subjected to significant anthropogenic pressures). The present action, supported by the Irstea-ONEMA action-sheet N ° 23 "Vegetal bio-indication in watercourses" (2016-2018), aimed to fill this regulatory deficit as quickly as possible by proposing a new national ad hoc system harmonized from the start, as far as possible, with the other European Member States. In that aim, the work carried out in the research team CARMA (now ECOVEA) consisted to: on the one hand, gather and analyze comparable national data obtained in a sufficiently homogeneous manner on these types of hydrosystems in the context of surveillance networks (IBD2007 data collected from 2007 to 2013); on the other hand, participate in a European exercise of intercalibration of the evaluation systems of such rivers, whose organization was concomitant to the realization of this national study. A first intercalibration exercise leaded by the "Large Rivers" X-GIG was carried out in 2012-2013 on various biological quality elements. In such circumstances, a bit too early compared to the progress of our own national reflection, France participated by providing data and as a mere external observer, but has not been subjected to the intercalibration. During this first exercise, participating countries were able to agree on a consensually defined default level of reference for this type of hydrosystems, and intercalibrated their national methods on that basis. A pressure-impact relationship between the PO4 content of waters and responses of the intercalibration common metric (diatomic ICM) has been established, from which a shared vision of good status of the LRs has been defined. Between 2015 and 2017, France took part in the second intercalibration exercise entitled "Fit-in exercise", leaded under the joint coordination of Bulgaria and Austria, which directly used the results previously obtained by the "LR" X-GIG and involved the participation of 8 different Member States. The results of this second collective exercise, communicated orally and informally during 2017, were validated through the official publication of the Decision EU 2018/229 (February 12th, 2018), authorizing at the same time the enforcement of the new evaluation system proposed by France in the context of that exercise. The incorporation of this new system inside an amendment to the French "Evaluation Decree" has therefore been proposed between October 2017 and February 2018, then signed (July 27th, 2018) and published at the JORF August 28th, 2018). The new assessment system is based on 3 evaluation grids that make it possible to assess in a differentiated and judicious way 3 types of large rivers (poorly-mineralized lowlands; mineralized lowlands; large rivers directly issued from mountain areas).
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D. Carayon, Juliette Tison-Rosebery, Michel Coste, François Delmas. Evaluation diatomique des Très Grands Cours d'Eau (TGCE) de France et intercalibration européenne : Rapport Final. [Rapport de recherche] irstea. 2018, pp.131. ⟨hal-02608976⟩

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