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
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
Modelling Microplastic Dynamics in Estuaries: A Comprehensive Review, Challenges and Recommendations
Abstract. 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
MODELLING SHORELINE DYNAMICS IN COMPLEX MACROTIDAL ENVIRONMENTS USING NEURAL NETWORKS
The aim of this work is to test an artificial intelligence approach with basic hydrodynamic and morphological variables, in order to assess the effectiveness of such methods in modelling complex beach dynamics. A simple feedforward neural network is used to evaluate the impact of selected variables on the prediction of the dynamics of specific shoreline isocontour proxies extracted from beach profiles, and to build a predictive model that could simulate the position of the proxies. The model was trained on datasets from two sites from the French coastal monitoring program DYNALIT, Porsmilin and Vougot beaches, and their profile measurements, water levels and wave measurements over 20 years. These two sites were selected due to differences in their morphology and hydrodynamics, as a means to assess the performance of neural networks over a larger variety of situations. A range of temporalities encompassing 3 days, 7 days, 14 days, and 30 days of selected hydrodynamic and morphological variables were used to study the impact time scales can have on modelled shoreline positions. The shoreline proxies used for Porsmilin and Vougot beaches correspond respectively to the berm and the contact between the dune toe and the upper beach, which can be assessed and followed along each beach profile. The shallow feedforward network included 1 hidden layer and 5 nodes, and was ran 50 times in order to assess the models' performance. The models were generally successful, with a blind shoreline prediction R of 0.88 in Porsmilin and 0.72 in Vougot. This artificial neural network (ANN) approach showed all-around better performance than previous beach equilibrium models, which is very encouraging regarding the prediction of future beach morphodynamics and the use of Machine Learning algorithms therein.
(07/04/2025)
UB, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, GEO-OCEAN, UBS, IFREMER, INSU - CNRS, UBO EPE, CNRS, LGO, UBS, IFREMER, UBO EPE, CNRS, LETG - Brest, UBO EPE, UR2, CNRS, LETG, UBO EPE, UR2, CNRS, Nantes Univ - IGARUN, LHSV, EDF R&D, EDF [E.D.F.], ENPC, IP Paris
Global impoverishment of natural vegetation revealed by dark diversity
Anthropogenic biodiversity decline threatens the functioning of ecosystems and the multiple benefits they provide to humanity1. Besides causing species losses in directly affected locations, human influence might also reduce biodiversity in relatively unmodified vegetation if far-reaching anthropogenic effects trigger local extinctions and hinder recolonisation. Here, we show that local plant diversity is globally negatively related to the level of anthropogenic activity in the surrounding region. Impoverishment of natural vegetation was only evident when we considered community completeness: the proportion of all suitable species in the region that are present at a site. To estimate community completeness, we compared the number of recorded species with the dark diversity — ecologically-suitable species that are absent from a site but present in the surrounding region2. In the sampled regions with minimal Human Footprint Index, an average of 35% of suitable plant species were present locally, compared with less than 20% in highly-impacted regions. Besides the potential to uncover overlooked threats to biodiversity, dark diversity also provides guidance for nature conservation. Species in the dark diversity remain regionally present, and their local populations might be restored through measures that improve connectivity between natural vegetation fragments and reduce threats to population persistence.
(Nature. vol. 641, n° 0028-0836, pp. 917-924, 02/04/2025)
U of S, UNIBO, MU / MUNI, CSIC, UV, UC Davis, UC, NINA, UNSW, FUM, NRCan, UAM, JCU, UHasselt, UiB, UPV / EHU, UB, UNCG, UNC, NUM, ESALQ, USP, MMU, UdeS, IPE - CSIC, CSIC, UNIVAQ, UNIPR, EPHE, PSL, LEHNA P3E, LEHNA, UCBL, ENTPE, CNRS, Uninsubria, UR EFNO, INRAE, CEN, UC, CAS, UNESP, HUN-REN, SGGW, ZHAW, CREAF, CSIC, UAB, IMBIV, CONICET, FCEFyN, iDiv, IB-CAS, CAS, UNIBE, TRU, UFRGS, UMR Eco&Sols, Cirad, IRD, INRAE, Institut Agro, UMR ECOFOG, Cirad, UG, CNRS, UA, INRAE, CRBE, IRD, CNRS, Toulouse INP, Comue de Toulouse, EPE UT, Comue de Toulouse, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Opportunities for Earth observation to inform risk management for ocean tipping points
As climate change continues, the likelihood of passing critical thresholds or tipping points increases. Hence, there is a need to advance the science for detecting such thresholds. In this paper, we assess the needs and opportunities for Earth Observation (EO, here understood to refer to satellite observations) to inform society in responding to the risks associated with ten potential large-scale ocean tipping elements: Atlantic Meridional Overturning Circulation; Atlantic Subpolar Gyre; Beaufort Gyre; Arctic halocline; Kuroshio Large Meander; deoxygenation; phytoplankton; zooplankton; higher level ecosystems (including fisheries); and marine biodiversity. We review current scientific understanding and identify specific EO and related modelling needs for each of these tipping elements. We draw out some generic points that apply across several of the elements. These common points include the importance of maintaining long-term, consistent time series; the need to combine EO data consistently with in situ data types (including subsurface), for example through data assimilation; and the need to reduce or work with current mismatches in resolution (in both directions) between climate models and EO datasets. Our analysis shows that developing EO, modelling and prediction systems together, with understanding of the strengths and limitations of each, provides many promising paths towards monitoring and early warning systems for tipping, and towards the development of the next generation of climate models.
(Surveys in Geophysics. vol. 46, n° 0169-3298, pp. 443–502, 01/04/2025)
MOHC, LOG, INSU - CNRS, ULCO, CNRS, IRD [Ile-de-France], LOCEAN-PROTEO, LOCEAN, MNHN, IRD, INSU - CNRS, SU, CNRS, IPSL (FR_636), ENS-PSL, UVSQ, CEA, INSU - CNRS, X, CNES, SU, CNRS, UPCité, ISMAR, CNR, PIK, GEOMAR, BOREA, UNICAEN, NU, MNHN, IRD, SU, CNRS, UA, JAMSTEC, NPS, GISS, GSFC, OCCR, UNIBE, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Chaetoceros Resting Spores Do Not Significantly Bias Sedimentary Diatom‐Bound Nitrogen Isotope Records Despite Distinctly Low Values
Abstract The nitrogen isotopic composition of diatom frustule‐bound organic matter (δ 15 N DB ) is often used to study changes in high latitude biological pump efficiency across glacial‐interglacial cycles, but the proxy may be biased by species‐specific effects. The genus Chaetoceros is of particular interest because of its abundance throughout ocean basins, its shifting biogeography during glacial periods, and the ability of many species to form heavily silicified resting spores. Here we investigate how Chaetoceros resting spores (CRS) record surface nitrate conditions in their nitrogen isotopic composition, and thus impact δ 15 N DB records, using assemblage‐specific sedimentary δ 15 N DB measurements and laboratory culture experiments. We find that fossil CRS from ODP Site 1098 record δ 15 N DB values 1.1–7.8‰ lower than non‐CRS diatoms in sediment. CRS grown in culture yield consistent results, recording δ 15 N DB values 2.6–8.2‰ lower than vegetative Chaetoceros in the same cultures. Low values are attributed to assimilation of isotopically light ammonium, heavy silicification, and/or internal nitrogen allocation processes during sporulation. Applying these findings to published δ 15 N DB records, variable CRS relative abundance in open ocean glacial sediments does not significantly bias δ 15 N DB records across glacial‐interglacial cycles, despite the large δ 15 N DB difference observed in CRS versus non‐CRS diatoms, due to the spores' small size.
(Paleoceanography and Paleoclimatology. vol. 40, n° 2572-4525, 01/04/2025)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS