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  • Le territoire régional est composé de taches urbaines de différentes tailles et formes, distribuées de manière variée. Les espaces urbains sont reliés les uns aux autres par le réseau routier, en particulier le réseau composé des routes primaires et secondaires. Cet espace urbain et routier ainsi composé est fortement artificialisé avec une forte composante d’imperméabilisation qui perdure au fil du temps. La dynamique spatiale et temporelle de cet espace peut être évaluée par les surfaces qui deviennent artificialisées, par la consommation des surfaces interstitielles, généralement agricoles ou naturelles. Ces surfaces à faible imperméabilisation, moins artificialisées, sont ainsi des îlots séparés les uns des autres par la trame urbaine et routière. Ces ilots sont de tailles variées et composent une structure fragmentée.Cet indice prend la forme d'une taille effective de maille, à savoir une grandeur qui exprime « la probabilité que deux points choisis au hasard dans un territoire [...] ne soient pas séparés par des obstacles tels que les voies de communication ou des zones bâties » (J. Jaeger, 2007).

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    Geodetic markers were installed along the main course of the Sélune. Physically marked out in the field, these markers have been located with a high-precision GPS (planimetric and z-precisions are given in the table). Please note that these markers may move slightly with the wetting/drying cycles of mainly clay soils, and their coordinates may be updated if necessary. Geodetic markers can be used as reference points to define a device or a new study area.

  • Les données de nodata par année (entre 2015 et 2019) correspondent aux zones de nuages et de leurs ombres portées sur les images satellites SPOT 6/7 utilisées pour la classification d'occupation du sol, donnée source pour les analyses géographiques qui ont suivi (extraction des espaces bâtis, des taches urbaines, indicateurs spatialisés)

  • La zone d'étude se situe au nord ouest du Sénégal et s'étale sur 5 100km². Elle inclue la ville de Thiès et une partie de la ville de Dakar, et remonte jusqu'à Kébémer, aux portes du désert de Loumpoul. La carte d'occupation 2018 a été réalisée à partir d'une image à Très Haute Résolution Spatiale (THRS) à 1.5m Spot6 acquise le 15/10/2010 et une série temporelle d'images Sentinel2 (résolution 10m) acquises entre le 01/01/2018 et le 31/12/2018. Le traitement a été réalisé via la chaine de traitement Moringa développée dans l'UMR TETIS. La méthodologie s'appuie sur une Segmentation Orientée Objet de l'image THRS puis d'une classification de chaque polygone (algorithme Random Forest) s'appuyant sur l'image SPOT6, la série temporelle Sentinel2, le SRTM à 30m et de nombreux indices calculés à partir de ces images (NDVI, indices de texture, pente,...). L’algorithme a été entrainé via un jeu de données acquises sur le terrain complété de données obtenues par photo-interprétation. Des corrections manuelles par photo-interprétation ont été réalisées afin d'améliorer le résultat. La précision globale est de 93%. La classification contient 13 classes d'occupation du sol : culture irriguée hors bas-fond, culture irriguée de bas-fond, culture pluviale, plantation, dune sable - arbustes, eau, savane arbustive, savane herbacée, sol nu, sol inondable, sol faiblement végétalisé, végétation naturelle dense et zone urbaine.

  • La densité de bâti est calculée par maille de 150 mètres de côté et sur la base d'une extraction du bâti à partir d'imagerie très haute résolution spatiale (1.5m) SPOT 6/7, pour les années 2015 à 2019.

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    Microbial communities play a major role in the functioning of ecosystems: they are at the base of the food chain (primary production) and participate in the degradation of organic matter. These communities are also known to respond rapidly to environmental changes. Like macro-invertebrates, they can be used as ecological indicators. Benthic diatoms are the main photosynthetic organisms in this biological community. The relative abundance of the different species is used to calculate an environmental quality index (EQI). Major differences in communities between the upstream and downstream zones were observed when the dams were in place. These differences will change once the dams are removed. As part of the Sélune observatory, pilot stations have been set up along the main course of the Sélune, distributed from upstream to downstream of the hydroelectric dams. Three stations are located in the former reservoirs of the dams, while the other two, known as the reference stations, are outside the area of influence of the former dams (one downstream and the other upstream). At these stations, aquatic biocenoses (including benthic macroinvertebrates, biofilms, macrophytes, etc.) are monitored. Since September 2014, the stations are ideally sampled every month from April to October (7 annual surveys) using artificial substrates (glass slides placed in the water). In addition to the diatom survey (floristic list, IBD calculation), the chlorophyll-a concentration is measured. During each campaign, an INRAe experimental sampling protocol is implemented. This protocol involves the immersion (1 month) of glass slides, an in situ measurement of the chlorophyll-a concentration via BentoTorch and then the collection of the biofilm on these glass slides. The biofilm is conditioned in (1) 99.9% ethanol to determine IBDs and floristic lists (outsourced service, based on standard NF T90-354) and (2) mineral water to measure chlorophyll-a concentration using a spectrometer. NB: the year 2023 is not covered in terms of measuring chlorophyll-a concentration via spectrometry due to a problem with the low-temperature storage of samples. This dataset provides measurements of the average daily concentration of chlorophyll-a and pheopigment in µg/cm2/day.

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    As part of the Sélune observatory, pilot stations have been set up along the main course of the Sélune, distributed from upstream to downstream of the hydroelectric dams. Three stations are located in the former reservoirs of the dams, while the other two, known as the reference stations, are outside the area of influence of the former dams (one downstream and the other upstream). At these stations, aquatic biocenoses (including benthic macroinvertebrates, biofilms, macrophytes, etc.) are monitored. 2 sampling campaigns (spring and autumn) for benthic macroinvertebrates (bmi) have been carried out since September 2014. During each campaign, 2 sampling protocols are implemented: - in accordance with standard NF T90-333, which enables the calculation of the IBG-DCE and I2M2 (‘SURBER’) - via artificial substrates immersed for 1 month (‘SUBART’), in order to focus on measuring the ‘effect of dams’. The protocol is described in: Piscart C., Moreteau, J.C., Beisel J.N. (2006). Monitoring changes in freshwater macroinvertebrate communities along a salinity gradient using artificial substrates. Environmental Monitoring and Assessment 116: 529-542. This layer details the benthic macroinvertebrate taxa and their abundance obtained after analysis (according to standard NF T90-388). These data are distributed by campaign and by sector. Taxa presenting all the morphological criteria clearly visible and characteristic allowing the exactitude of their determination and an irreproachable state of conservation are integrated into the reference collection of the Sélune Observatory. This collection can be consulted on request (see contact point). Taxon determination is based on version v17 of the TAXREF reference. The dataset is currently under embargo.

  • Categories  

    Microbial communities play a major role in the functioning of ecosystems: they are at the base of the food chain (primary production) and participate in the degradation of organic matter. These communities are also known to respond rapidly to environmental changes. Like macro-invertebrates, they can be used as ecological indicators. Benthic diatoms are the main photosynthetic organisms in this biological community. The relative abundance of the various species is used to calculate an environmental quality index (EQI). Major differences in communities between the upstream and downstream zones were observed when the dams were in place. These differences will change once the dams are removed. As part of the Sélune Observatory, the stations are sampled every month from April to October (7 annual surveys) using artificial substrates (glass slides placed in the water). In addition to the diatom survey (floristic list, IBD calculation), the chlorophyll a concentration is measured. This layer gives the IBD and EQR (normalised) index value for a station during a campaign.

  • Categories  

    Microbial communities play a major role in the functioning of ecosystems: they are at the base of the food chain (primary production) and participate in the degradation of organic matter. These communities are also known to respond rapidly to environmental changes. Like macro-invertebrates, they can be used as ecological indicators. Benthic diatoms are the main photosynthetic organisms in this biological community. The relative abundance of the various species is used to calculate an environmental quality index (EQI). Major differences in communities between the upstream and downstream zones were observed when the dams were in place. These differences will change once the dams are removed. As part of the Sélune observatory, pilot stations have been set up along the main course of the Sélune, distributed from upstream to downstream of the hydroelectric dams. Three stations are located in the former reservoirs of the dams, while the other two, known as the reference stations, are outside the area of influence of the former dams (one downstream and the other upstream). At these stations, aquatic biocenoses (including benthic macroinvertebrates, biofilms, macrophytes, etc.) are monitored. Since September 2014, the stations are ideally sampled every month from April to October (7 annual surveys) using artificial substrates (glass slides placed in the water). In addition to the diatom survey (floristic list, IBD calculation), the chlorophyll-a concentration is measured. This layer shows the location of the study sectors used to monitor photosynthetic biofilms and the campaigns carried out.