MAGEST: Rapport scientifique sur les données 2024
Le rapport scientifique sur les données acquises en 2024 par le réseau MAGEST présente l’ensemble de ces données, avec la production de nombreuses figures permettant d’illustrer la variabilité spatio-temporelle des paramètres suivis (température, salinité, turbidité/charges en matières en suspension, oxygène dissous). Le bilan de la disposition oxygène du SAGE Estuaire de la Gironde est également détaillé et comparé à ceux des années précédentes. L’année 2024 se classe au 4ème rang des années les plus chaudes depuis le début du XXème siècle et au 7ème rang des années les plus pluvieuses depuis 1959. Le mois de septembre 2024, marqué par d’importantes précipitation et frais a mis fin à un étiage peu sévère. Ces conditions climatiques ont permis d'améliorer nettement la qualité physico-chimique des eaux des estuaires nord-aquitains par rapport aux deux années précédentes (très chaudes et marquées par de forts déficits hydrologiques). Les faits marquants du réseau MAGEST de l’année 2024 sont : - des températures moyennes journalières comprises entre 6,4 et 28,3 °C, avec un été plus tempéré d’au moins 1 °C qu’en 2023 ; - une intrusion saline, définie par une salinité (moyenne journalière) supérieure à 0.5, d’intensité et de durée très réduites (29 jours à Tonnay-Charente, 11 jours à Bordeaux) ; - une arrivée tardive (juillet) et un départ précoce (fin octobre) du bouchon vaseux à l’aval de la Charente, de la Dordogne et de la Garonne ; - des désoxygénations estivales modérées à Tonnay-Charente et à Bordeaux ; aucun site n’a enregistré des moyennes journalières < 4 mg L-1 en 2024. Les objectifs de la disposition oxygène du SAGE Estuaire de la Gironde (seuil de moyenne journalière) n’ont pas été atteints à Bordeaux, avec un total de 20 jours sous le seuil de 5 mg L-1, dont 15 jours successifs du 23 août au 6 septembre. À Libourne, les objectifs ont été atteints de justesse avec 4 jours sous le seuil objectif de 5 mg L-1. À Tonnay-Charente, il y a eu 11 jours compris entre 4 et 5 mg L-1, un bilan bien meilleur qu’en 2023 où 39 jours avaient été enregistrés des concentrations inférieures à 3 mg L-1. Enfin, deux articles d'intérêt général parus récemment sont présentés.
(19/04/2025)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Temporal Distribution of Microplastics and other Anthropogenic Particles in Abiotic Compartments of a Coastal Lagoon from the Atlantic Coast
This study characterizes anthropogenic particles (AP) and microplastics (MP) in treated wastewater, sea surface, water column and intertidal sediments from the Arcachon Bay (France) at four seasons. Their morphometric characteristics, polymer types and concentrations were described. Concentrations showed some seasonal variations that may be related to anthropogenic factors like tourism or fishing. Overall, 2687.4 ± 1335.2 AP.m−3 (614.7 ± 481.4 MP.m−3) were found in wastewater and we estimated that 127.4 ± 41.6 million of AP (30.0 ± 25.2 million of MP) could enter the Atlantic Ocean each day via the wastewater system. Mean concentrations at sea surface, in water column and intertidal sediments were respectively 0.79 ± 1.64 AP.m−3 (0.62 ± 1.30 MP.m−3), 778.90 ± 370.95 AP.m−3 (319.2 ± 214.6 MP.m−3) and 86.93 ± 67.77 AP.kg−1 (16.1 ± 19.1 MP.kg−1 dry weight). Finally, we proposed insights about sources of AP and MP based on their characteristics (e.g. textiles, tyres, fishing).
(Water, Air, and Soil Pollution. vol. 236, n° 0049-6979, pp. 342, 16/04/2025)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, OFB, UB, CBMN, UB, ENITAB, INC-CNRS, CNRS
Physiological responses to light regime of a Mediterranean lagoon strain of Chaetoceros tenuissimus and a collection strain of Chaetoceros calcitrans
Abstract Diatoms play a fundamental ecological role as primary producers in aquatic food webs. Among these, a little number of solitary species of the genus Chaetoceros are of great interest as live food for aquaculture, including major taxa like Chaetoceros calcitrans which have been well studied in terms of growth and essential lipid content. In contrast, the globally distributed species Chaetoceros tenuissimus has not been investigated as a potential live prey for aquaculture. For a preliminary analysis of the effect of culture conditions on growth and biomass content of a new strain of C. tenuissimus (CT16ED, hereafter CTEN) isolated from a Mediterranean lagoon, we first considered the light regime, comparing cultivation under a light–dark (L:D) cycle (12:12 h L:D photoperiod) and under continuous light, which conditions were also applied to a C. calcitrans strain, CCAP1085/3 (CCAL). Both strains had a similar growth rate under continuous light, but growth rate was lower in CTEN than in CCAL under the L:D cycle. Photosynthetic pigments content was higher under the L:D cycle than under continuous light in both strains, and higher pigment content was found in CCAL than in CTEN, indicating different photoacclimation. The lipid content of CTEN did not change markedly with photoperiod or growth phase, unlike CCAL. Both strains had high proportions of essential lipids, particularly n-3 polyunsaturated fatty acids, including EPA and DHA, but these varied less in CTEN than in CCAL. CTEN was richer in DHA (22:6n-3) with a more balanced DHA:EPA ratio. From these results, a potential interest of CTEN for use in aquaculture is discussed, with regard to its nutritional quality (essential lipid content), its growth, and its high-light niche offering possibilities for cultivation in outdoor systems in the Mediterranean area.
(Journal of Applied Phycology, n° 0921-8971, 15/04/2025)
SPE, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, UMR MARBEC, IRD, IFREMER, CNRS, UM, LEMAR, IRD, IFREMER, UBO EPE, CNRS, CRO
Modélisation de l’effet des phénomènes de bypass sédimentaire sur l’évolution moyen à long terme du trait de côte
Sous l’effet des courants induits par les vagues, le sable peut contourner les obstacles rocheux naturels ou artificiels présents sur la plage via un phénomène nommé bypass sédimentaire. Le bypass joue un rôle clé dans l’évolution des plages, notamment les plages en baie délimitées par deux obstacles rocheux qui représentent environ la moitié des plages dans le monde. Pourtant, ce phénomène est souvent mal pris en compte dans les modèles d’évolution du trait de côte, voire absent. L’objectif de cette thèse est ainsi d’étendre le champ d’application du modèle à complexité réduite LX-Shore en y implémentant une paramétrisation du bypass sédimentaire. La nouvelle version du modèle, intégrant l’impact du bypass subaquatique, est testée sur une plage en baie idéalisée soumise à diverses conditions de vagues d’incidence variable. Les résultats montrent que la prise en compte du bypass impacte significativement la forme moyenne de la plage et la variabilité spatiale du trait de côte, notamment en termes de rotation, courbure et maximum d’érosion. Des applications sur des plages réelles présentant des épis rocheux (au Danemark et à Fréjus) ou un ouvrage de défense longitudinal (Lacanau) ont permis d’explorer l’influence du bypass à différentes échelles de temps : à l’échelle évènementielle, à l’échelle annuelle et à l’échelle pluri-décennale, sous l’effet de l’élévation du niveau marin. En intégrant pour la première fois une paramétrisation générique du bypass sédimentaire dans un modèle à complexité réduite, ces travaux contribuent à améliorer la compréhension et la modélisation de l’évolution du trait de côte en présence d’obstacles rocheux, offrant ainsi de nouvelles perspectives en termes de gestion des zones côtières.
(15/04/2025)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Water quality of spawning grounds constrains the population dynamics of an emblematic diadromous species (Alosa alosa)
In this study, the role of water quality has been studied to assess its suitability for the allis shad (Alosa alosa), a diadromous fish for which abundance has drastically declined at the beginning of 2000 and is remaining critically low in the Garonne basin (France). The water quality regarding contamination at spawning grounds and its toxicity for embryos and larvae is one possible explanatory factor for this decline, which has not been investigated. Early life stages of fish are particularly sensitive to environmental conditions, including water contamination, making them useful for environmental monitoring. The ex situ biomonitoring method allows continuous exposure of organisms to river water while controlling for confounding factors such as temperature, oxygen, and photoperiod. Three ex situ exposures of allis shad embryos to the Garonne water were conducted during its spawning season, in spring 2022 and 2023, under optimal temperature and oxygen saturation rate. Survival in the control groups demonstrates the value of the ex situ approach, allowing for the exposure of early life stages in their natural environment. Results indicated a high mortality rate in embryos exposed to the Garonne water compared to control, with mortality occurring during organogenesis, which is a particularly critical period of development. These findings raise concerns about the suitability of the Garonne water for the early development of allis shad and consequently for the population dynamics of this species in the Garonne basin. Moreover, these results confirm previous approaches of risk assessment and experimentations, suggesting that water quality and contamination could have an impact on other fish species.
(Environmental Biology of Fishes. vol. 108, n° 0378-1909, pp. 821 - 834, 12/04/2025)
UR EABX, INRAE, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, UMR ISPA, Bordeaux Sciences Agro, INRAE, RiverLy, INRAE
Beach morphodynamic response to tropical storms using a spatio-temporal surrogate model. Case study in Martinique
Tropical cyclones (TCs), especially intense hurricanes, pose a significant threat to coastal areas due to the destructive forces of storm surges and wind-generated waves. These forces can cause severe coastal erosion and flooding within a few hours. The present study aims to address the limitations of computational cost of morphodynamic models and data scarcity by developing a surrogate model to better address the morphodynamic beach response to storms event. Few studies have focused on developing surrogate models specifically dedicated to temporal coastal beach erosion forecast. A great subset of TC is selected from a synthetic database, considering time-dependent evolution of the oceanographic variables. Secondly, a 2d XBeach model is used to compute the morphological responses to selected storms. Thirdly, we adapt and test an Artificial Neural Network-based surrogate model to mimic XBeach at low computational cost. Results are presented at the study site of Le Carbet Beach, Martinique, Lesser Antilles
(07/04/2025)
BRGM, UniFE, UM, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Regional assessment using public webcams of the role of post-storm recovery in the seasonal variability of beach width
Understanding the mechanisms and times required for beaches to recover after extreme storms, as well as the effect of these episodic setbacks on long-term coastal erosion trends, is crucial for anticipating changes and implementing effective management strategies. A storm can have significant impacts on the coastline, resulting in retreats of several meters within hours. The natural recovery of the beach in the hours/days following a storm varies greatly between sites, ranging from a few days to several months. In this study, we examine the regional variability in coastal response during winter storms and post-storm recovery, using a beach width indicator obtained through the analysis of public webcam images on event, seasonal, and multi-year time scales. Video-derived shoreline positions were used to calculate weekly average beach widths at 11 sites along the coastline of Occitanie. The analysis demonstrated that storm responses and seasonal trends exhibit significant variability despite similarities in morphologies, and exposure to storm waves. Although post-storm recovery following the major events of 2021 and 2022 was nearly complete and very rapid for most sites, some beaches experienced prolonged recovery periods, requiring several months to return to their initial position. While the results indicated that storm events were sufficiently spaced to allow these beaches to recover, a series of events in autumn 2023 raises questions about this recovery capacity and underscores the potential impact of singular events on medium- and long-term coastal evolution trends.
(. vol. 2, 07/04/2025)
BRGM, UniFE, UM, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
From fixed to transgressive coastal dunes, the conditions and timing of the transition along the Aquitaine coast, France
Today most of the coastal dunes in temperate latitudes, especially in the northern hemisphere, are relatively stable. However, over the last decade, the Gironde coast has experienced substantial dune remobilization following a major marine erosion event. The qualities of the dataset used (continuity in time and space) based on annual airborne LiDAR and Satellite imagery (Sen-tinel-2) allow a detailed description of the morphological change and establish relations with forcing and controlling factors (vegetation cover, geomorphological descriptors). Between 2014 and 2023, about 10 km of the Gi-ronde dunes have switched from fixed dunes to transgressive dunes. The analysis showed that in the vast majority of the cases the dominant process involved was dune front cannibalism. However, there is considerable spatial and temporal variability in the transition to a transgressive dune along the coast, depending on the amount of sediment remobilized and the morphological parameters of the dunes (steepness of the front slope, width).
(07/04/2025)
BRGM, UB, UPVD, ONF, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Modelling Microplastic Dynamics in Estuaries: A Comprehensive Review, Challenges and Recommendations
The study of microplastic transport and fate in estuaries poses significant challenges due to the complex, dynamic nature of these ecosystems and the diverse characteristics of microplastics. Process-based numerical models have become indispensable for studying microplastics, complementing observational data by offering insights into transport processes and dispersion trends that are difficult to capture through in-situ measurements alone. Effective model implementations require an accurate representation of the hydrodynamic conditions, relevant transport processes, particle properties, and their dynamic behaviour and interactions with other environmental components. In this paper, we provide a comprehensive review of the different process-based modelling approaches used to study the transport of microplastics in estuaries, including Eulerian Idealized 2DV models, Eulerian Realistic Models, Lagrangian Particle Tracking Models, and Population Balance Equation Models. We detail each approach and analyze previous applications, examining key aspects such as parameterizations, input data, model setups, and validation methods. We assess the strengths and limitations of each approach and provide recommendations, good practices, and future directions to address challenges, improve the accuracy of predictions, and advance modelling strategies, ultimately benefiting the research field.
(Geoscientific Model Development. vol. 18, n° 1991-9603, pp. 7227-7255, 07/04/2025)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, SIAME, UPPA, MIO, IRD, AMU, INSU - CNRS, UTLN, CNRS
Observations and modelling of coastal dune dynamics along the Gironde Coast, France
Considered as reservoirs of biodiversity, coastal dunes also represent natural barrier against coastal flooding and large source of sediment to mitigate coastal erosion. Dynamics of coastal dunes are forced and controlled by marine, aeolian and biological processes. A better understanding of the interactions between all these processes based on field observations or numerical modelling is crucial to define management strategies that aim to develop the resilience of coastal dune against sea level rise. The analysis of multi-annual topographic data collected along the Gironde coast in SW France show a strong landward migration of the coastal dunes caused by strong wind events and a decrease in vegetation cover. The same data were also used to calibrate and validate a numerical model, AeoLiS, that simulated Aeolian sediment transport. This model showed good performance to reproduce the landward migration of non-vegetated dune.
(07/04/2025)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS