Assessing the role of riparian vegetation and land use on river ecological status using remote sensing and spatial modelling

International audiencePreserving or restoring the ecological quality of aquatic ecosystems is a major objective of Water Framework Directive. A pending question deals with the gain in river ecological status indicators that could be allowed by restoring riparian tree vegetation. In order to quantify in a statistically relevant way the role of riparian vegetation on river ecosystems, a regional approach is required that mobilizes three complementary fields of research : (1) the use of very high spatial resolution satellite imagery to map river corridor land use and riparian vegetation along large river networks ; (2) the design and quantification of synthetic spatialized indicators of river corridor land use; (3) the development of pressures/state spatialized models that quantify the relation between river corridor land use indicators and river water bodies ecological status indicators. The corresponding methods were developed and implemented on various river basins, particularly over lower Normandy river networks (6000 km long; 157 ecological stations). Results show for instance that in this region, changing the local land use along a river from agriculture to forest (over a buffer 1km long and 30m large on both sides of the river) allows in average to increase by 0.3 points the river ecological status indicators (EQR-IBGN between 0 and 1). Such results are of high interest for decision-makers that can estimate the interest of investing in restoration strategies by anticipating their effect in terms of Water Framework Directive standards

Analyse à l'échelle régionale de l'impact de l'occupation du sol dans les corridors rivulaires sur l'état écologique des cours d'eau

This work focuses on the spatial characterization and quantification of the influence of surrounding pressures (land cover at different scales, from watershed to local riparian corridor) on the ecological status of rivers. Addressed at the regional level the study pays particular attention to riparian corridors for their interest in developing strategies for the preservation and restoration under the European Framework Directive on Water. It relies on the development of robust and reliable methodologies concerning (i) fine-scale mapping of land cover within riparian corridors, (ii) construction of spatial indicators reflecting this occupation and (iii) building pressures / impacts models quantifying links between land cover within riparian corridors and the ecological state of aquatic environments. The results using these methodological advances have demonstrated the value The results using these methodological advances have demonstrated the value of having a land cover data at Very High Spatial Resolution over large areas and using indicators calculated within a wide range of riparian footprints reflecting the impact mechanism of a given land cover category on the ecological status to improve the identification and location of sources of pressure in these spaces. They also highlight at regional level the significant role of riparian plant communities on ecological status of rivers, both on a band 20 m on either side of the watercourse.Ce travail porte sur la caractérisation spatiale et la quantification de l'influence des pressions environnantes (occupation des sols à différentes échelles, du bassin versant amont au corridor rivulaire local) sur l'état écologique des cours d'eau. Abordée au niveau régional l'étude porte une attention particulière aux corridors rivulaires pour leur intérêt dans l'élaboration de stratégies de préservation et de restauration en application de la Directive Cadre européenne sur l'Eau. Elle repose sur le développement de méthodologies robustes et fiables (i) de cartographie fine de l'occupation des sols dans les corridors rivulaires, (ii) de construction d'indicateurs spatialisés traduisant cette occupation et (iii) de modélisation pressions/impacts quantifiant le lien entre occupation des sols dans les corridors rivulaires et état écologique des milieux aquatiques. Les résultats utilisant ces avancées méthodologiques montrent l'intérêt de disposer d'une donnée d'occupation du sol à Très Haute Résolution Spatiale sur de grands territoires, d'indicateurs calculés sur différentes emprises spatiales au niveau du corridor qui traduisent les mécanismes d'impacts d'une catégorie d'occupation du sol donnée sur l'état écologique pour améliorer l'identification et la localisation des sources de pressions dans ces espaces. Ils mettent en évidence également au niveau régional le rôle significatif des formations végétales rivulaires locales sur l'état écologique des cours d'eau, ceci sur une bande de 20 m de part et d'autre du cours d'eau

Couleur des eaux continentales : Exploitation de l’imagerie Sentinel-2 et Landsat-5, 7, 8

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CES - Couleur des eaux continentales Exploitation de l’imagerie Sentinel-2 et Landsat-1..8

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GRS processor: Glint removal for Sentinel-2 scheme and application to Sentinel -2 and Landsat-5, 7, 8

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Exploitation of SENTINEL-2 time series for monitoring ecological quality parameters of french lakes and reservoirs (TELQUEL project)

International audienceThe ability to understand the close links between lacustrine environments and the human-altered landscapes in which they are embedded in depends strongly on the spatiotemporal availability and quality of key bio-optical parameters such as transparency, Chlorophyll A concentration (ChlA), Colored Dissolved Organic Matter (CDOM) absorption coefficient, Inorganic Suspended Matter (ISM) concentration. However, the current European monitoring based on the data collected from field observations do not characterize finely and reliably the spatiotemporal dynamics of these parameters. As an example, for the application of the Water Framework Directive in France, on the one hand only 380 lakes/reservoirs are monitored among the 480 involved water bodies, and on the other the collected measurements remains very punctual and discontinuous in time (four dates per year every 6 years). Remote sensing technique is often portrayed as a powerful tool to overcome this difficulty, as it provides synoptic and accurate spatio-temporal information on the desired bio-optical parameters. However, the different "ocean color" sensors that are able to monitor these parameters, such as SeaWiFS (1km, NASA), MODIS (250 m, NASA), MERIS (300 m, ESA), have a spatial resolution which is often too low to correctly study the majority of lake/reservoir ecosystems. Typically, only 2% of 480 French lakes/reservoirs are overlapped by at minimum 5 pixels of 250-m spatial resolution. The successful launch of Sentinel-2 satellite that carries the Multi-Spectral Instrument (MSI) sensor allows interesting research perspectives to monitor bio-optical properties of these lakes/reservoir due to (i) its high spatial resolution (typically between 10 m and 60 m); (ii) its suitable signal to noise ratios, and (iii) its good spectral performances (13 bands). The presentation aims at describing an ongoing project so-called TELQUEL. The main objectives of this project are to provide bio-optical algorithms for MSI/Sentinel-2 data to retrieve the water transparency, and ChlA, CDOM and ISM concentrations. The first step consists in developing a specific atmospheric correction algorithm over lake areas that takes into account the altitude effects and the adjacency effects induced by the land surface surrounding the lakes. The second step of the project consists of establishing bio-optical relationships between MSI/Sentinel-2 reflectances and the concentrations of biogeochemical parameters. A final step is dedicated to use the retrieved bio-optical properties and suspended matter concentrations for enhancing the lake water quality evaluation and simulation. We will focus our presentation on the methodological approach to correct for the atmospheric effects for lake/reservoir targets (dark target). Preliminary results on the bio-optical relationships obtained over the test-site of the project, namely the Naussac reservoir (10 km²) (close to Le Puy-en-Velay, France) will be presented

TELQUEL project : Calibrating bio-optical models for retrieving ecological parameters of lakes from SENTINEL-2 and LANDSAT 8

International audienceThe main objective of the TELQUEL (TELédétection de la Qualité Ecologique des Lacs) project is to provide quantitative remotely sensed observations to monitor the ecological state of the French lakes. In this direction, MSI/Sentinel-2 and OLI/Landsat 8 data are exploited to : (i) identify/develop a specific atmospheric correction and deginting algorithm over lake areas (see Poster from Harmel, T. et al. in this conference); (ii) provide bio-optical algorithms to retrieve water transparency and water constituent concentrations (Chl-a, CDOM and TSM), first results are shown in this poster. (iii) use the retrieved bio-optical properties and matter concentrations for enhancing the lake water quality evaluation and biogeochemical models