Geomorphological control of sandy beaches by a mixed-energy tidal inlet
Coastal areas adjacent to tidal inlets are highly valuable areas for marine ecosystems where a wide range of social and economic activities can be found. These areas can be differentiated from open coast due to their specific morphological behaviour caused by a complex nearshore bathymetry and interactions between wave and tidal forcing. The understanding of these interactions is usually limited by the lack of a systemic approach and the scarce availability of comprehensive datasets covering subtidal, intertidal and supratidal areas at large spatial and temporal scales. Here, the complementary use of different bathymetric and topographic datasets and the development of innovative methods using satellite imagery, offers the opportunity to develop a comprehensive understanding of the timescales and the key processes involved in the dynamics of tidal inlets and its control on the downdrift coast. The use of satellite-derived bathymetric maps, computed over the last two decades, showed two sequences of 8 and 9 years where large sandy shoals migrated along the tidal inlet and welded onto the downdrift coast. Although the study period covers one of the most energetic winter over the last decades, the most significant sediment volume changes (±300 m3/m) observed along the three kilometres of beach located south to the inlet were mostly attributed to the migration and welding of these sandy shoals, whereas the offshore wave forcing was of secondary importance. It was also demonstrated that these migrating and welding events had an impact on the pattern of the nearshore bathymetry and sandbars down to 10 km south to the inlet. Primary welding events near to the inlet are associated to the formation of kilometre-long and alongshore uniform nearshore sandbars that subsequently migrate further down the coast causing secondary welding events. The ability to understand and define the spatial and temporal boundaries at which beach behaviour is controlled by a local tidal inlet gives the opportunity to develop sediment compartment approach in order to make accurate predictions of future beach behaviour.
(Marine Geology. vol. 450, n° 0025-3227, 01/08/2022)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, BRGM
Effects of Stochastic Wave Forcing on Equilibrium Shoreline Modelling Across the 21 st Century Including Sea-Level Rise
Coastal communities are currently facing the challenge of climate change and coastal retreat. While scientists are moving towards ensemble-modelling approaches to address uncertainties on shoreline evolution predictions, they rarely account for the stochastic nature of wave conditions across a variety of temporal scales (e.g., daily, weekly, seasonal, and interannual). In this contribution, we investigate the effects of the inherent variability of wave conditions on past and future multi-decadal shoreline evolution at the, cross-shore transport dominated, beach of Truc Vert (France). Using a climate-based wave emulator and variance decomposition method, we address the relative impacts of uncertain wave chronology, sea-level rise and model free parameters on modelled shoreline change, while accounting for possible correlations and interactions among the input variables. This work is done for two different wave-driven equilibrium models. The results show that the equilibrium shoreline models respond differently to the ensemble wave forcing, with strong implications on the long-term variability of modelled shoreline. We find that the modelled shoreline variance is primarily driven by the uncertain wave chronology until mid-21 st century, while the uncertainties on future sea-level rise become dominant after 2060 in all the simulated scenarios. We also found that interactions and correlations among the uncertain variables can affect the estimation of shoreline predictions uncertainties. Finally, we provide a perspective on the application of non-stationary wave-related model parameters as future research avenue for understanding uncertainties in modelled shoreline.
(Coastal Engineering. vol. 175, n° 0378-3839, pp. 104149, 01/08/2022)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, BRGM, UC / UniCan
Crossing the Boundaries: How Key Advancements in Understanding of Headland Sediment Bypassing Improves Definition of Littoral Cells
Headland sediment bypassing connects short-term physical forcing and long-term morphological response. The contributions from King et al., 2021 are a substantial step in understanding the complexities by combining field observations, process-based numerical modeling, and empirical generalization with the development of an improved parametrization of headland sediment bypassing. This study adds to the growing body of knowledge about littoral cell boundaries, or as proposed in this commentary, littoral cells that respond to varying wave energy and water levels that may influence the results from shoreline position models. Evolution of the shoreline in the context of climate change can be better understood by considering variability in littoral cell boundaries.
(Journal of Geophysical Research. Oceans. vol. 127, n° 2169-9275, 01/08/2022)
NOAA, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Impacts of chemical stress, season, and climate change on the flounder population of the highly anthropised Seine estuary (France)
The main objective of this study was to improve our knowledge on the responses of fish populations to multistress (diffuse pollution and warming waters) in estuaries. Adult flounders were caught in two estuaries in the Eastern English Channel: the heavily polluted Seine estuary vs the moderately contaminated Canche estuary. Fish samplings were conducted in January just before the reproduction period, and in July when gonads were at rest. The overall rise in coastal winter water temperatures detected over the Channel impairs the flounder's phenology of reproduction in the two estuaries, inducing a delay of maturation process and probably also spawning. The higher liver histopathology index in Seine vs Canche could be the consequence of the fish exposition to a complex cocktail of contaminants in a strongly industrialized estuary. Higher levels of neurotoxicity, gill lipid peroxidation, and liver EROD activity were observed in Seine vs Canche. Furthermore, a possible impairment in mitochondrial metabolism was suggested in the Seine flounder population. We confirmed in this study the potential role of two membrane lipids (sphingomyelin and phosphatidylserine) in the resistance towards oxidative stress in Seine and Canche. Finally, we suggest that the Seine flounder population (and possibly the connected Eastern English Channel flounder populations over the French Coast) could be seriously impacted in the future by multistress: higher winter temperatures and chemical contamination.
(Environmental Science and Pollution Research. vol. 29, n° 0944-1344, pp. 59751-59769, 01/08/2022)
LEMAR, IRD, IFREMER, UBO EPE, CNRS, Cedre, LASIRE, INC-CNRS, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, LIEC, INSU - CNRS, UL, CNRS, GIP-Seine-Aval, LEHNA IAPHY, LEHNA, UCBL, ENTPE, CNRS, LOG, INSU - CNRS, ULCO, CNRS, IRD [Ile-de-France], ULCO
Early molecular responses of mangrove oysters to nanoplastics using a microfluidic device to mimic environmental exposure
This study assessed the effects of nanoplastics (NPs) using for the very first time microfluidic devices (chip) mimicking transition waters. Three kinds of NPs were tested: crushed NPs from polystyrene pellets (NP-PS), or from Guadeloupe beaches (NP-G); and latex PS (PSL-COOH). The eluted fractions from the microfluidic device showed a low aggregation of NPs. They remained stable over time in the exposure media, with a stabilization of NPs of small sizes (< 500 nm). These chips were thus used for the toxicological assessment of NPs on swamp oysters, Isognomon alatus. Oysters were exposed for 7 days to the chip elution fraction of either NP-G, NP-PS or PSL-COOH (0.34 to 333 µg.L-1). Gene transcription analyses showed that the tested NPs triggered responses on genes involved in endocytosis, mitochondrial metabolism disruption, oxidative stress, DNA repair, and detoxification. Highest responses were observed after NP-G exposure at low concentrations (1 µg.L-1), as they are originated from the natural environment and accumulated contaminants, enhancing toxicological effects. As salinity influences aggregation and then the bioavailability of NPs, our results demonstrated the importance of using microfluidic devices for ecotoxicological studies on swamp or estuarine species.
(Journal of Hazardous Materials. vol. 436, n° 0304-3894, pp. 129283, 01/08/2022)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, GR, UR, INSU - CNRS, CNRS, IPR, UR, CNRS, ULaval
The Impacts of Precipitation on Fluorescent Dissolved Organic Matter (FDOM) in an Urban River System
Precipitation is considered a key factor influencing the fluorescent dissolved organic matter (FDOM) of urban rivers. However, the multiple effects of precipitation on FDOM in urban rivers and the long-term impacts of precipitation on the spatial patterns of FDOM are seldom known. Spatiotemporal variations of FDOM at 36 sites from the urban rivers of Jinan City during dry and wet seasons were investigated in this study. Four components were identified using an excitation–emission matrix and parallel factor analysis. Overall, the total fluorescence intensities in dry and wet seasons ranged from 6.59 to 35.7 quinine sulfate units (QSU) and 3.42 to 69.3 QSU, respectively. Significant variations were found for different components that C2 and C3 declined but C4 increased in the wet season (p < 0.05). The temporal variations for different components could be explained by the different combined effects of precipitation dilution and flushing. Three different reference FDOM sources, including background water, spring water, and wastewater treatment plant (WWTP) outlets, were illustrated using principal coordinate analysis (PCoA). The places of FDOM in most sites were more closed to the PCoA location of WWTP outlets in the dry season while central shifted in the wet season. The changes of FDOM sources in the wet season could be explained by the mixed effect of precipitation. In conclusion, this study provided new insights into the multiple impacts of precipitation on FDOM in urban river systems, and also data support for precise pollution discharge and water resource management.
(Water. vol. 14, n° 2073-4441, pp. 2323, 27/07/2022)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Distribution spatiale et temporelle des microplastiques et particules anthropiques au sein d'une lagune côtière mésotidale, le Bassin d'Arcachon. Approche multi-compartiments.
Le plastique est un matériel peu cher, léger et résistant, ce qui l’a rendu rapidement indispensable dans tous types de secteurs tel que celui de l’emballage alimentaire, du médicale ou encore de l’automobile et du bâtiment. Néanmoins, ces extraordinaires propriétés ont aussi contribué à son actuelle omniprésence dans l’environnement marin, de manière parfois insidieuse. En effet, une fraction souvent invisible à l’œil nu, nommée microplastique (MP) est aujourd’hui étudiée avec intérêt. Les MP sont principalement définis par une taille inférieure à 5 mm, bien que la limite inférieure soit encore discutée au sein de la communauté. Dans le même temps, d’autres types de particules manufacturées par l’homme sont de plus en plus fréquemment décrites, tel que des fragments caoutchouteux noirs ou des fibres. Ces particules anthropiques (AP), MP inclus, ont été détectées dans l’ensemble des compartiments aquatiques (e.g. eau de surface et colonne d’eau) et le compartiment sédimentaire (e.g. plages, sédiments subtidaux et intertidaux) et dans un grand nombre d’espèces dans toutes les régions océaniques. Cependant, leur présence n’est pas anodine car les MP peuvent modifier certains cycles géochimiques, mais aussi biologiques. Par exemple, du fait de leur petite taille, ils peuvent interagir avec une très large gamme d’espèces aquatiques allant du zooplancton aux cétacés. Hors, dans le Bassin d’Arcachon, une pression anthropique importante découle de l’attractivité et de la richesse de cette lagune (e.g. pêche, conchyliculture et tourisme). Par ailleurs, ce système lagunaire est complexe de par sa morphologie (e.g. chenaux et zones intertidales) et son fonctionnement hydrodynamique est marqué principalement par les marées. Ainsi, ce projet de recherche doctoral a permis d’établir un état des lieux de la contamination par les MP et autres particules anthropiques au sein du Bassin d’Arcachon (notamment des fibres). Plus particulièrement, nous avons 1) quantifié et caractérisé les AP et MP présents dans différents compartiments de cette lagune (eau de surface, colonne d’eau, sédiment intertidaux, laisse de mer, organismes aquatiques), 2) déterminé leur distribution spatiale (depuis la zone océanique jusqu’aux limites continentales du bassin) et exploré la dynamique de leur transport entre les compartiments, 3) caractérisé l’évolution temporelle de la contamination au sein de ces compartiments.
(19/07/2022)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, CBMN, UB, ENITAB, INC-CNRS, CNRS
Trajectories of legacy and emerging metal contaminants in French river sediments
Trace metals and metalloids (TMMs) are substancesdisseminated in the critical zone (CZ) as a result of i. mechanicalerosion processes or chemical alteration of bedrocks anduncontaminated soils, and ii. releases from multiple sourcesrelated to anthropogenic activities during several millennia. Inrivers, legacy and emerging TMMs, including Rare EarthElements (REEs), are predominantly or partially adsorbed onsuspended particulate matter. Therefore, riverine transport ofnatural and anthropogenic TMMs depends on hydraulicconditions, and storage occurs in depositional zones (e.g.reservoirs, floodplains, ponds). As rivers are the receptacle formany substances released into the CZ, analysing temporal trendsof TMMs in dated sediment cores can reflect the trajectory ofcontaminant pressure in watersheds, as sediments are consideredas testimonies of past and current anthropogenic activities, andmay provide information about the potential future impacts ofemerging pollutants.This study aims at establishing regional geochemicalbackgrounds (RGB) and the trajectories of legacy and emergingTMMs in dated sediment cores at the outlets of the main Frenchriver watersheds (Rhône, Loire, Eure-Seine, Lot-Garonne).These investigations are supported by temporal TMM and REEtrends in watersheds characterized by contrasting geologicalfeatures. Preliminary results showed that mean REEconcentrations are approximatively twice higher in sedimentdeposits collected in the Loire River than in the Seine and RhoneRivers for which mean REE contents are relatively similar.Moreover, European Shale (EUS)-normalized concentrations ofREEs highlighted positive anomalies of light- and medium-REEsas Cerium (Ce), Samarium (Sm), and Europium (Eu). Theseanomalies determined in the Rhône and Loire Rivers, and in theEure-Seine continuum have not been systematically measured inthe most recent deposits as expected. As REE anomalies are notexclusively due to anthropogenic signals, but may also derivefrom lithology (calcareous versus crystalline rocks) andbiogeochemical processes, it appears essential to discriminate thecontributions of anthropogenic signals and RGB to totalconcentrations. Based on these results, we discuss the potentialof increasingly used Technology-Critical Elements (TCEs),recorded in sediment archives, as markers of the beginning of the4th industrial revolution.
(10/07/2022)
M2C, UNICAEN, NU, INSU - CNRS, UNIROUEN, NU, CNRS, COBRA, IRCOF, UNIROUEN, NU, INSA Rouen Normandie, INSA, NU, CNRS, UNIROUEN, NU, INSA Rouen Normandie, INSA, NU, INC3M, UNICAEN, NU, ENSICAEN, NU, ULH, NU, UNIROUEN, NU, INSA Rouen Normandie, INSA, NU, INC-CNRS, CNRS, INC-CNRS, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, IRSN/PSE-ENV/SRTE/LRTA, IRSN/PSE-ENV/SRTE, IRSN, IRSN/PSE-ENV/SAME/LMRE, IRSN/PSE-ENV/SAME, IRSN, LEHNA, UCBL, ENTPE, CNRS, GéHCO, UT, IRSN/PSE-ENV/STAAR/LRTA, IRSN/PSE-ENV/STAAR, IRSN
Genetic improvement of shoreline evolution forecasting models
(pp. 1916-1923, 09/07/2022)
LEGOS, IRD, UT3, Comue de Toulouse, INSU - CNRS, CNES, CNRS, ISAE-SUPAERO, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, IRD, CNES
Machine-Learning Functional Zonation Approach for Characterizing Terrestrial–Aquatic Interfaces: Application to Lake Erie
Ecosystems at coastal terrestrial–aquatic interfaces play a significant role in global biogeochemical cycles. In this study, we aimed to characterize coastal wetlands with particular focus on the co-variability between plant dynamics, topography, soil, and other environmental factors. We proposed a functional zonation approach based on machine learning clustering to identify the spatial regions, i.e., zones that capture these co-varied properties. This approach was applied to publicly available datasets along Lake Erie, in the Great Lakes Region. We investigated the heterogeneity of coastal ecosystem structures as a function of along-shore distance and transverse distance, based on the spatial data layers, including topography, wetland vegetation cover, and the time series of Landsat’s enhanced vegetation index (EVI) between 1990 and 2020. Results showed that the topographic metrics (elevation and slope), soil texture, and plant productivity influence the spatial distribution of wetland land-covers (emergent and phragmites). These results highlight a natural organization along the transverse axis, where the elevation and the EVI increase further away from the coastline. In addition, the clustering analysis allowed us to identify regions with distinct environmental characteristics, as well as the ones that are more sensitive to interannual lake-level variations.
(Remote Sensing. vol. 14, n° 2072-4292, 08/07/2022)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS