Satellite-derived shoreline data assimilation for sandy coast evolution
Understanding and predicting the evolution of sandy shorelines remains a central challenge in coastal science and a critical requirement for sustainable management. Reliable predictions require consistent observations and models capable of representing complex, non-stationary morphodynamic behaviour. This thesis advances shoreline change modelling by integrating publicly available datasets—primarily satellite-derived shoreline (SDS) observations—within calibration and data assimilation frameworks, assessing their added value. By relying exclusively on freely accessible data, the work establishes a transparent, transferable modelling foundation applicable even in data-limited coastal environments. The initial focus is on 1D equilibrium shoreline models, addressing calibration using uncorrected, noisy SDS data without tidal adjustments or a priori site knowledge. Using a simulated annealing algorithm, robust model calibrations were achieved at Truc Vert beach, a fully exposed, wave-dominated site with high-energy waves, large tides, complex intertidal bathymetry, and mild nearshore slopes that introduce substantial observational uncertainty. The strong model performance under these challenging and conservative conditions demonstrates that valuable information can be extracted from low-quality SDS, supporting broader applicability where simple equilibrium models are suitable. Applying uncorrected SDS in sequential data assimilation proved more challenging due to observation noise limiting the algorithm’s ability to track system non-stationarity. To explore the potential of time-varying model free parameters, in situ observations were used to assess links to wave climate and influence on predictive skill. Across multiple sites along the European Atlantic coast, the connection between parameter variability and climate was weak or absent, suggesting non-stationarity primarily reflects local morphodynamic adjustments. Non-stationary models showed slightly improved performance at some sites and reduced skill at others, with data quality influencing outcomes—sites with higher-quality observations benefited more. Notably, nonstationary models captured extremes of erosion, demonstrating their potential for representing rare but significant events, though stronger gains would require regions with multimodal wave climates. Building on these insights, calibration and data assimilation were combined in an international benchmark experiment at a site in Australia documented with SDS data and historical aerial photographs. Two distinct equilibrium-based models were explicitly coupled within a hybrid framework, illustrating how calibration and assimilation can complement each other. This approach highlights the potential of ad hoc hybrid modelling strategies that merge separate empirical formulations to capture multi-scale shoreline dynamics within reduced-complexity frameworks. Finally, the framework was extended to a quasi-2D configuration using grid-based data assimilation with spatial nudging. Applied to the highly dynamic Sacalin spit in the southern Danube delta, where dominant processes are not explicitly represented in the model, the approach successfully constrained shoreline evolution across the grid and improved agreement with long-term satellite observations. Although neighbouring grid dependencies were not yet considered, this implementation represents a critical step toward fully 2D assimilation capable of resolving spatial feedbacks in shoreline evolution. Overall, this work demonstrates that combining long-term satellite observations with hybrid modelling and data assimilation provides a powerful pathway for advancing understanding, prediction, and eventually operational forecasting of shoreline change in complex coastal systems.
(08/12/2025)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Marine parasite diversity : study of cockle-trematode systems and their phenology using an environmental DNA-type approach
Digenean trematodes are among the most important groups of macroparasites in marine environments and play an important role in ecosystem functioning. Understanding their ecology requires accurate species identification and detection. However, conventional methods based on morphology have limitations, particularly for differentiating morphologically similar or cryptic species, identifying undescribed parasite stages and detecting early-stage or low intensity infections of hosts. As a result, life cycles and infection phenology often remain unresolved. Molecular approaches have the potential to overcome these barriers and help fill these ecological knowledge gaps. This thesis investigated how molecular tools can complement or surpass morphological identification in the diverse trematode community infecting the edible cockle (Cerastoderma edule), a key bivalve species of ecological and economic importance in European intertidal ecosystems, such as Arcachon Bay (France). Field surveys, laboratory experiments as well as morphological and molecular analyses were undertaken to (1) determine the reliability of morphological identification through comparison with molecular phylogenetic analyses of trematodes infecting cockles across Europe; (2) apply a targeted environmental DNA (eDNA) approach to elucidate the life cycle of the himasthlid Curtuteria arguinae by identifying its unknown hosts and assess the environmental drivers of its transmission to cockles; (3) improve detection of Bucephalus minimus sporocyst infections, a highly pathogenic bucephalid trematode, using species-specific molecular assays in order to describe its infection phenology. The European survey revealed 13 trematode species in cockles by morphology, but phylogenetic analyses uncovered 17 distinct genetic lineages. While some species were correctly identified morphologically, many were prone to misidentification or showed unexpected, potentially cryptic diversity, especially within the Himasthlidae family. This work clarified the strengths and limitations of current morphological methods of species identification and revealed that unknown infections might be more common than expected. The DNA dataset generated here also provided a solid foundation for the design of species-specific molecular tools. Building on this, a targeted qPCR-based eDNA approach allowed detection of C. arguinae DNA in water and fecal samples. The needle snail (Bittium reticulatum) and the oystercatcher (Haematopus ostralegus) were thereby identified respectively as the first intermediate host and as the definitive host, elucidating the life cycle for the first time. Experiments showed cercarial emergence was strongly temperature-dependent, driving seasonal transmission to cockles in the field. These results explain the parasite’s southern distribution and suggest potential northward expansion under climate change. Finally, molecular detection of B. minimus in cockles by species-specific qPCR and dPCR assays revealed substantially higher prevalence than microscopy, allowing the first description of infection phenology in Arcachon Bay. Infection dynamics were linked to cockle size and life history, as well as seasonal migration of the definitive host, the European seabass (Dicentrarchus labrax). Altogether, this thesis demonstrates the value of molecular methods for trematode identification and detection. These case studies show how molecular approaches, such as targeted eDNA approaches, can help resolve life cycles, detect inconspicuous infections and improve understanding of parasite phenology. Beyond the cockle-trematode systems studied here, this work highlights the broader value of molecular tools for assessing parasite prevalence, distribution and transmission and better integrating trematodes in our understanding of marine ecosystem functioning.
(05/12/2025)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
How does habitat use influence PFAS contamination in wildlife? Combining stable isotopes and GPS tracking in three gull species
Per-and polyfluoroalkyl substances (PFAS) are toxic and persistent compounds widely distributed in the environment and accumulate in top predators, including seabirds. Because of the biomagnification potentials of some PFAS, diet is thought to be a key exposure route for PFAS. However, other factors, such as habitat use, may mask interspecific differences in PFAS exposure expected from trophic structure. Among seabirds, gulls are generalist that forage in both terrestrial and marine habitats, making them relevant models to concurrently investigate the influence of foraging habitats and trophic position on PFAS exposure. We combined plasma PFAS concentrations with GPS tracking and stable isotopes to define foraging habitats (δ 13 C; δ 34 S; GPS) and trophic positions (δ 15 N) in three sympatric gull species breeding in France (Isle of Ré). In herring gulls (Larus argentatus), long-chain perfluoroalkyl carboxylic (PFCAs) were positively correlated with high trophic resources from marine habitats. We found compound-and sex-dependent relationships between PFAS concentrations and stable isotope values in lesser black-backed gulls (Larus fuscus), while no association was found with habitat use. No association was found between PFAS levels and stable isotopes in great blackbacked gulls (Larus marinus). Our study suggests that coastal habitat could be a source of PFCA contamination and highlights that the influence of habitat use on gull exposure to PFAS varied depending on species, sex, and compounds.
(Environmental Pollution, n° 0269-7491, 01/12/2025)
SU, CEBC, ULR, CNRS, INRAE, LIENSs, INSU - CNRS, ULR, CNRS, LPO, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, ULR
Endocrine effects of Imazalil on aromatase expression, vitellogenesis and ovarian histology using cyp19a1a-eGFP-casper transgenic zebrafish
Considering the hazards and risks posed by endocrine disrupting chemicals (EDC) to organisms, there is a need to study their effects. To that end, transgenic fish are powerful models that can provide mechanistic information regarding the endocrine activity of test chemicals. In this study, we used a newly developed transgenic zebrafish line (cyp19a1a-eGFP-casper) in the OECD 21-day fish assay (OECD TG 230) to provide additional mechanistic insight on Imazalil (IMZ; 1.9; 9.9 and 140.7 μg/L). After 21 days of exposure to IMZ, the circulating concentrations of 17-β-estradiol (E2) and vitellogenin decreased in females, reflecting the aromatase activities inhibition. Exposure to 140.7 μg/L of IMZ for 21 days also resulted in a change in the proportion of the different oocyte stages in the ovaries, with an accumulation of large oocytes in exposed females. In addition to the classical endpoints, in vivo GFP fluorescence was quantified in the ovaries during the time course of the exposure to follow gonadal aromatase expression. After seven days of exposure, ovarian aromatase expression increased in females exposed to medium and high concentrations of IMZ, persisting over the 21-day of exposure in fish from the highest concentration group and reflecting a compensatory response to the aromatase enzymatic activities inhibition. Results from the present study provided valuable information on the mode of action and the effects of IMZ in zebrafish. Transgenic zebrafish exposure to IMZ caused a cascade of responses consistent with effects reported for wild-type fish exposed to azole fungicides, both qualitatively and quantitatively. The cyp19a1a-eGFP (-casper) transgenic zebrafish lines, allowed in vivo monitoring of gonadal aromatase expression in a time- and concentration-dependent manner thereby demonstrating their relevance to provide complementary mechanistic information on aromatase in regulatory assays such as OECD TG 230.
(Aquatic Toxicology. vol. 289, n° 0166-445X, pp. 107580, 01/12/2025)
INERIS, SEBIO, INERIS, URCA, ULH, NU, URCA, CNRS, LPGP, Biosit : Biologie - Santé - Innovation Technologique, INRAE, LPTC, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, UMR MARBEC, IRD, IFREMER, CNRS, UM
Relating estuarine turbidity maxima to tide and river conditions
Tidal rivers and estuaries may experience high levels of suspended particulate matter (SPM), which impacts water quality and ecosystem functioning. The processes controlling the development of estuarine turbidity maxima (ETM) are fairly well understood. However, predicting the maximum SPM concentration in an estuary based on aggregated parameters (estuarine dimensions, river discharge, tidal range) remains, up to now, impossible without extensive in-situ measurements and/or numerical models. This study introduces an approach that links the strength of the ETM to the tidal, river, and morphological characteristics of a system. Using in-situ data from contrasting meso- to macro-tidal estuaries, we found a consistent pattern of maximum SPM concentrations within a two-dimensional parameter space. The resulting turbidity diagram reveals a high SPM hotspot in estuaries with specific forcing conditions, corresponding to intermediate relative tidal amplitudes and freshwater Froude numbers. This multi-site research advances our predictions of ETM intensity in tide-dominated estuaries, offering a straightforward method to explore potential turbidity trajectories under various human pressures.
(Scientific Reports. vol. 16, n° 2045-2322, pp. 3096 (11p.), 01/12/2025)
DYNECO, IFREMER, IOW, BAW, M2C, UNICAEN, NU, INSU - CNRS, UNIROUEN, NU, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, IRSTEA, TU Delft
Toward a typology of river functioning: a comprehensive study of the particulate organic matter composition at the multi-river scale
In river systems, particulate organic matter (POM) originates from various sources with distinct dynamics related to production, decomposition, transport, and burial, leading to spatiotemporal heterogeneity in the POM pool. This study uses C and N isotope and element ratios, Bayesian models and multivariate analyses to (1) quantify relationships between POM composition and environmental forcings, and (2) propose a typology of river functioning based on POM composition and their seasonal dynamics. Twenty-three temperate rivers, representing a large diversity of temperate conditions, were sampled fortnightly to monthly over one to seven years at their River-Estuary Interface (REI). Phytoplankton and labile terrestrial material were found in all rivers, while sewage and refractory terrestrial material appeared in a few. Across all rivers, phytoplankton dominance correlated with agricultural surfaces, labile terrestrial material with organic-rich leached soil, and refractory terrestrial matter with steep, soil-poor catchments. Seasonal dynamics mainly depended to phytoplankton growth, river discharge, and sediment resuspension. Statistical regionalisation identified four river-dynamics types: (1) POM is dominated by labile terrestrial material year-round; (2) POM is composed of labile and refractory terrestrial material plus phytoplankton with variable seasonality; (3) POM is composed of phytoplankton and labile terrestrial material without pronounced seasonality; and (4) POM is composed of phytoplankton and labile terrestrial material with pronounced seasonality. This research offers a comprehensive understanding of POM composition, dynamics, and drivers at the REI in temperate climates, complementing similar study in coastal systems. Future similar research on estuaries is called to refine knowledge along the Land-Ocean Aquatic Continuum.
(Biogeosciences. vol. 22, n° 1726-4170, pp. 7363-7401, 27/11/2025)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, LERPC, COAST, IFREMER, IPREM, UPPA, INC-CNRS, CNRS, CRESCO, MNHN, IFREMER, CEFREM, UPVD, INSU - CNRS, CNRS
ClimLoco1.0: CLimate variable confidence Interval of Multivariate Linear Observational COnstraint
Projections of future climate are key to society's adaptation and mitigation plans in response to climate change. Numerical climate models provide projections, but the large dispersion between them makes future climate very uncertain. To refine them, approaches called observational constraints (OCs) have been developed. They constrain an ensemble of climate projections using some real-world observations. However, there are many difficulties in dealing with the large literature on OC: the methods are diverse, the mathematical formulation and underlying assumptions are not always clear, and the methods are often limited to the use of the observations of only one variable. To address these challenges, this article proposes a new statistical model called ClimLoco1.0, which stands for “CLimate variable confidence Interval of Multivariate Linear Observational COnstraint”. It describes, in a rigorous way, the confidence interval of a projected variable (its best guess associated with an uncertainty at a confidence level) obtained using a multivariate linear OC. The article is built up in increasing complexity by expressing three different cases – the last one being ClimLoco1.0, the confidence interval of a projected variable: unconstrained, constrained by multiple real-world observations assumed to be noiseless, and constrained by multiple real-world observations assumed to be noisy. ClimLoco1.0 thus accounts for observational noise (instrumental error and climate-internal variability), which is sometimes neglected in the literature but is important as it reduces the impact of the OC. Furthermore, ClimLoco1.0 accounts for uncertainty rigorously by taking into account the quality of the estimators, which depends, for example, on the number of climate models considered. In addition to providing an interpretation of the mathematical results, this article proposes graphical interpretations based on synthetic data. ClimLoco1.0 is compared to some methods from the literature at the end of the article and is used in a real case study in the appendix.
(Geoscientific Model Development. vol. 18, n° 1991-9603, pp. 9015-9038, 25/11/2025)
ASTRAL, IMB, UB, Bordeaux INP, CNRS, Inria, UB, Bordeaux INP, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Response of phytoplankton communities to the onset of the 2020 summer marine heatwave in the Drake Passage and Antarctic Peninsula
Abstract. Extreme warming events are increasingly more intense and frequent in the global ocean. These events are predicted to drive profound and widespread effects on marine ecosystems, yet their impact on phytoplankton, the base of the marine food web, is still largely unknown. Our understanding of the impact of these phenomena in marine ecosystems is particularly poor in the remote and logistically challenging Southern Ocean. During summer 2020, the research vessel Hespérides sampled the water column of the Drake Passage and northern Antarctic Peninsula before (early January) and during the early phase (late January-early February) of a Marine Heat Wave (MHW), that resulted in sea surface temperature anomalies of up to +3 °C. Here, we take advantage of this exceptional opportunity to document the effects of an extreme warming event on the nutrient and phytoplankton (diatom and coccolithophores) distributions across the main zonal systems of the Southern Ocean. Overall, our results indicate that biogeographical variability of diatom and coccolithophore assemblages, the two dominant phytoplankton groups in the Southern Ocean, mirrored the physical and chemical properties of the water masses delineated by the Southern Ocean fronts before and during the onset of the marine heat wave. Analysis of a suite of satellite-derived oceanographic parameters revealed that development and persistence of the 2020 marine heat wave were closely tied to mesoscale anticyclonic eddy dynamics. The increase in sea surface temperatures during the onset of the marine heat wave was associated with a remarkable increase in diatom abundance reaching bloom concentrations and a shift in the diatom assemblage towards an increase in the relative abundance of the small diatom Fragilariopsis cylindrus/nana in the southern Drake Passage. Notably, the diatom bloom was not coupled with a statistically significant change in chlorophyll a, as derived from in-situ fluorescence, or modelled Net Primary Production. It is likely that the differing contribution of other phytoplankton groups and/or a shift in the average phytoplankton size before and during the MHW might be responsible for these results. Average coccolithophore abundance was lower than previous studies in the Drake Passage and decreased during the MHW. We speculate that the remarkable nitrate decrease by approximately one order of magnitude lower than average summer concentrations might have been responsible for the reduction in coccolithophore numbers. Low nitrate levels are attributed to either the advection of nitrate poor waters from lower latitudes by an anticyclonic eddy and/or nutrient consumption by substantial development of soft-tissue phytoplankton biomass. Overall, our results reinforce the notion that a warmer Southern Ocean will favour an increase of small phytoplankton cells in the southern Drake Passage and northern Antarctic Peninsula with unpredictable consequences in the marine-food web and biogeochemical cycles that need to be urgently quantified and parametrized.
(Biogeosciences. vol. 22, n° 1726-4170, pp. 7205 - 7232, 25/11/2025)
ICMAN, CSIC, EPHE, PSL, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, UB, IACT, CSIC, UGR, IGME, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, GEOTRAC, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, JAMSTEC
What environmental and human factors influence the decision of a beachgoer to enter the water at a high-energy beach? Application to South Western France
Background Coastal areas are among the most attractive destinations worldwide, but engaging in water-based recreational activities is not without risk. The overall bathing risk ultimately results from the combination of natural physical hazards (e.g. rip currents, shore break waves) and the individuals who expose themselves to them. Among the growing body of beach safety studies, many have identified the lack of exposure data as a severe limitation (1). A first attempt to address this was made by considering the beachgoer population rather than the total population to assess incident rates (2). We believe our research takes a step further by estimating the proportion of beachgoers who enter the water on a given day. Methods We built a unique multidisciplinary database combining data collected by an on-site beachgoers survey, weather stations, marine buoys and tidal reconstruction. We employed a logistic regression analysis to predict beachgoer’s decision to enter the water on any given day at a high-energy recreational beach. Results We demonstrated that both environmental and human factors influence a beachgoer’s decision to enter the water. Daily mean wave height and daily mean insolation duration were significant predictors at the p<0.001 level, while age, place of residence and self-confidence in swimming out of a rip current were significant at the p<0.05 level or higher. Our model has an accuracy, F-Score, precision and recall of 71%, 73%, 86%, 79% respectively. Conclusion Beachgoer exposure on any given day can ultimately be predicted by coupling our model with beach attendance models (3). This would allow for the design of rescue and preventive operations on days with high expected exposure. While models based solely on environmental factors can be used to forecast beach risks, incorporating human factors into the model provides valuable insight for crafting prevention messages. To this end, forecasting tools must be based on behavioural analytical framework as much as possible
(20/11/2025)
UR ETTIS, INRAE, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
From Fields to Homes: How Agricultural Pesticides Contaminate Residential Environments? Findings from the PESTIPREV Study, France
Pesticide sprayings on crops can contaminate nearby homes, yet factors driving pesticide penetration indoors remain poorly understood. Our objective was to study the influence of factors related to air exchange and occupants track-in on agricultural pesticide surface loadings (SLs) measured in homes near vineyards. Indoor surface wipes were collected in 31 homes near vineyards during the peak pesticide application season in 2020 and 2021 and analyzed via LC/MS/MS or GC/MS/MS. Questionnaire data provided information on air exchange and track-in factors. Linear mixed models assessed their effects on SLs of seven fungicides across all surfaces (n = 667) and stratified by recently cleaned surfaces (n = 217), floors (n = 105), and high dusty surfaces (n = 130). Daytime airing reduced floor SLs by 14–28%, depending on the pesticide, but increased SLs by up to 38% on high surfaces. Nighttime airing was associated with a 20–65% increase in recently cleaned surface SLs. Double-flow ventilation increased high surface SLs by 21–126%, while ventilation grids reduced contamination, especially on floors (up to 51%). Home insulation tended to raise SLs. Pets and gardening were the main sources of pesticide track-in, contributing to an 11–87% increase in floor SLs. However, pets substantially reduced SLs on high surfaces. Direct yard access increased SLs in rooms by 5–10%. Room occupancy and outdoor activities showed mixed effects depending on the surface, whereas shoe removal and doormat use showed no significant impact. While ventilation effects remain complex to interpret for prevention, track-in findings suggest hygiene measures could help reduce indoor pesticide SLs.
(Water, Air, and Soil Pollution. vol. 237, n° 0049-6979, pp. article no 150, 19/11/2025)
BPH, UB, INSERM, CHU Bordeaux, ARS NA, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, ECOSYS, INRAE