Fossil pigments and environmental conditions in the oligotrophic Laja Lake in the Chilean Andes
Interactions among climate change, ozone depletion, and ultraviolet radiation affect aquatic ecosystems. Meteorological and biological monitoring is often too brief, however, to record the magnitudes of past changes in ultraviolet fluxes and their effects. This study presents an analysis of fossil pigments and environmental conditions in the oligotrophic Laja Lake in the Chilean Andes over a 60-year period. The age of the sediment core was determined using high-efficiency gamma spectrometry and dated with lead-210 (210Pb). Analysis of the total and specific fossil pigments from a sediment core utilized a combination of analytical methods, spectrophotometry, and high-performance liquid chromatography. Environmental variables, such as stratospheric ozone concentration, temperature, precipitation, and ultraviolet radiation explained changes in the fossil pigment scytonemin.. Results showed that low cloud cover over the high mountain lake predominated, with high ultraviolet radiation and temperature values during summer months. The most abundant group was Bacillariophyceae (diatoms). The highest concentrations of the pigments (canthaxanthin echinenone, myxoxanthophyll, aphanizophyll zeaxanthin and scytonemin) that represent the cyanobacteria groups were found in the upper part of the core (cm 0–15). The trend analysis further suggested that the influence of environmental features enabled generation of ultraviolet radiation-shielding pigment in the algae communities in the high mountain lake.This study advances understanding of the interactive effects of climate change, ozone depletion, and ultraviolet radiation on aquatic ecosystems. Fossil pigments proved to be good indicators of lake-ecosystem response to climate/environmental changes, which are necessary for predicting possible effects of future climate change.
(Anthropocene. vol. 37, n° 2213-3054, pp. 100321, 01/03/2022)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Hydro-sedimentary dynamics of the Rance estuary : processes, evolution and management
The Rance estuary is a relatively small low-discharge steep-sided ria, located along the Brittany coast in northern France, with a maximum spring tidal range of 13.5 m. Taking advantage of this hyper-tidal regime, the first operational tidal power station (TPS) in the world (and currently the second largest) was built at the estuary’s mouth and has been in operation since the 1960s. In addition to the TPS, the Rance estuary is characterized by its complex morphology and the configuration of its uppermost limit (Chatelier lock).Net siltation and sediment accumulation were reported in the basin since the 1980s by various studies based on field measurements. However, the impact of the TPS on hydrodynamics, sediment transport and morphodynamic is still unquantified. In addition, the relevance of each physical processes driving hydrodynamics and sediment dynamics in this complex system is still unclear.This PhD thesis aims to better understand hydro-sedimentary dynamics in this highly engineered system by the presence of a tidal power plant on its mouth and a lock on its uppermost limit.To this goal, a complementary approach accounting for both field measurements and numerical modelling was deployed. On the one hand, field surveys of hydro-sedimentary variables were carried out to calibrate and validate the numerical models. On the other hand, 2D and 3D hydro-sedimentary numerical models were developed in the TELEMAC-MASCARET modelling system.Numerical results reveal that the TPS induces (i) a major decrease in tidal range and tidal prime along with the increase of submerged intertidal zones; (ii) a limitation of high-water level inside the estuary protecting it against marine flooding; and (iii) an overall decrease in currents except in the region close to the TPS. Moreover, the morphology of the estuary amplifies ebb currents in the narrowing at Saint-Hubert-Port. Furthermore, the TPS pushes the freshwater-saltwater interface roughly 5km upstream in the estuary. Its position is also sensitive to seasonal river discharge variation.The 3D hydro-sedimentary model shows that at the scale of a tidal cycle (i) peak suspended sediment concentrations (SSC) are noticed during the estuary's infilling phase; and (ii) sediment could be resuspended locally during the turbining phase (electricity production stage), but would not be transported further than 3km from the uppermost limit. At the scale of a fortnight, residual sediment flux is continuously oriented towards the upper estuary. Consequently, significant sedimentation rates were observed in the main upstream channel. This morphodynamic behavior was also captured by the model under natural tidal forcing (without TPS), but with lower sedimentation rates. At the time-scale of one year, 2D hydro-sedimentary numerical results assess the need to provide an accurate river discharge considering hydraulic flushes to correctly simulate long term morphodynamic processes.Furthermore, hydraulic flushes at the Chatelier lock and the opening of sluice gates during ebb prove their efficiency in decreasing sediment accumulation in the upper estuary. Finally, the complementary 2D and 3D numerical models showed to be invaluable tools to define a sustainable management plan of the Rance estuary.
(23/02/2022)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Modelling past and future sandy shoreline change and the respective uncertainties : toward a holistic approach
Shoreline change along sandy coasts responds to a myriad of processes interacting at different spatial and temporal scales, making shoreline predictions challenging. Shoreline modelling inherits uncertainties from the primary driver boundary conditions (e.g. sea-level rise and wave forcing) as well as uncertainties related to model assumptions and/or misspecifications of the physics. Despite the recent progresses in addressing uncertainties related to sea-level rise (SLR), the uncertainties related to wave-driven shoreline response are still poorly understood. This thesis gathers wave-driven equilibrium shoreline models, SLRdriven recession models, and variance decomposition methods into a probabilistic framework to investigate the roles of several sources of uncertainty in modelled shoreline change. The framework is applied to analyse the uncertainties associated with past and future multi-decadal shoreline evolution at the cross-shore transport dominated sandy beach of Truc Vert (France). As the physics of the combined action of waves and sea-level rise has not yet been described in detail, the thesis also presents a novel physical interpretation of the beach response to sea-level rise to support the integration of SLR-driven recession into equilibrium shoreline models. Shoreline response under the coupled effects of waves and SLR reveals complex patterns and interplays of the several contributions of uncertainties to shoreline predictions. Overall, uncertainties on Truc Vert shoreline predictions across the 21st century are driven by the uncertain model free parameters and wave conditions over the first half of the century. Then, the uncertainties on SLR become the dominant driver over the last decades. When uncertainties on SLR are negligible, the uncertainties of wave conditions variability are responsible for up to 83% of the uncertainties in modelled shoreline. It is also observed that the uncertainties in modelled shoreline trajectories depend on the underlying physical assumptions of different equilibrium shoreline models and future climate scenario.
(10/02/2022)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Predicting drowning from sea and weather forecasts: development and validation of a model on surf beaches of southwestern France
Objective To predict the coast-wide risk of drowning along the surf beaches of Gironde, southwestern France. Methods Data on rescues and drownings were collected from the Medical Emergency Center of Gironde (SAMU 33). Seasonality, holidays, weekends, weather and metocean conditions were considered potentially predictive. Logistic regression models were fitted with data from 2011 to 2013 and used to predict 2015-2017 events employing weather and ocean forecasts. Results Air temperature, wave parameters, seasonality and holidays were associated with drownings. Prospective validation was performed on 617 days, covering 232 events (rescues and drownings) reported on 104 different days. The area under the curve (AUC) of the daily risk prediction model (combined with 3-day forecasts) was 0.82 (95% CI 0.79 to 0.86). The AUC of the 3-hour step model was 0.85 (95% CI 0.81 to 0.88). Conclusions Drowning events along the Gironde surf coast can be anticipated up to 3 days in advance. Preventative messages and rescue preparations could be increased as the forecast risk increased, especially during the off-peak season, when the number of available rescuers is low.
(Injury Prevention. vol. 28, n° 1353-8047, pp. 16-22, 01/02/2022)
BPH, UB, INSERM, CHU Bordeaux, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Status of Dieldrin in vegetable growing soils across a peri-urban agricultural area according to an adapted sampling strategy
Since the fifties, organochlorine pesticides (OCPs) had been used in agriculture to protect vegetables. Two decades after their ban by the Stockholm convention in 2001, OCPs are still present in agricultural soils inducing vegetable contamination with concentrations above Maximum Residue Level (MRL). This is a major concern for a 5 km2 peri-urban vegetable growing valley located in the south west of France. In the present work, the sampling method was developed to clarify the spatial distribution of one OCP, Dieldrin, and its relationship with soil properties at the scale of study area. A total of 99 soil samples was collected for physicochemical analyses and Dieldrin concentrations. Results show Dieldrin concentrations in soils up to 204 μg kg−1. The horizontal distribution of this pesticide is heterogeneous at the study area scale but homogeneous in each reference plot studied. About 85% of the contamination was located in the top soil layers (0–40 cm depth), but Dieldrin may still be quantified at a depth of 80 cm. Among all soil physicochemical parameters analysed, SOM was the most significantly related (P < 10−4) with Dieldrin concentrations, once different grain size fractions were considered. Moreover, results indicate a 33 times higher Dieldrin concentration and/or extractability for coarse sand than for other grain size fractions. These results show that the developed sampling method is adapted for the study area scale as it helps understanding the factors influencing the spatial distribution of Dieldrin. Historical amendments are the predominant factor for the horizontal contamination and deep ploughing for the vertical contamination. Also, the variations of coarse sand repartition in soils prevents identification of relationships between SOM and Dieldrin contamination in bulk soil. Further investigation is required to explain these relationships but these results highlight why no clear relationship between OCPs and SOM was previously identified.
(Environmental Pollution. vol. 295, n° 0269-7491, pp. 118666, 01/02/2022)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, Bordeaux INP, UBM
Foraminiferal Distribution in Two Estuarine Intertidal Mudflats of the French Atlantic Coast: Testing the Marine Influence Index
This study focuses on the foraminiferal distribution on intertidal mudflats of two contrasted estuaries (Auray and Vie) along the French Atlantic coast. In both estuaries, the foraminiferal communities are dominated by Haynesina germanica and the Ammonia tepida group. Stations located near the outlets show a high diversity and abundance of species of the genus Elphidium. Stations in the inner estuary show a higher proportion of agglutinated species (Ammotium salsum, Ammobaculites agglutinans). Multivariate statistical analysis suggests that the distance to the sea and the percentage of fine sediment (<63 µm) are the two main parameters explaining the foraminiferal distribution. Chemical analyses of the sediment show that the two studied estuaries are not affected by major anthropogenic pollution, so that the faunas should mainly reflect the natural controlling parameters. Three indices of environmental quality commonly used in coastal areas show counter-intuitive differences between stations, suggesting that these indices may be less reliable for use in intertidal estuarine mudflats. The newly developed Marine Influence Index (MII) integrates three major ecological factors: the position of the sampling point on the salinity gradient, the emergence time at low tide and the relative importance of fresh water discharge. In our dataset, MII shows significant correlations with the controlling environmental parameters (distance to the sea, percentage grains < 63 µm), as well as with the foraminiferal patterns (PCA axis 1, species richness, percentage of Elphidium spp. and Quinqueloculina spp.). These results suggest that the MII explains a substantial part of the faunal variability on estuarine intertidal mudflats, and can be used to detect deviations from the natural distribution patterns in response to anthropogenic pollution.
(Water. vol. 14, n° 2073-4441, pp. 645, 01/02/2022)
LPG, UM, UA, INSU - CNRS, CNRS, Nantes univ - UFR ST, Nantes Univ, UNINE, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, IRHS, UA, INRAE, Institut Agro, IRHS-SMS, IRHS, UA, INRAE, Institut Agro
Ocean Productivity in the Gulf of Cadiz Over the Last 50 kyr
Reconstructions of ocean primary productivity (PP) help to explain past and present biogeochemical cycles and climate changes in the oceans. We document PP variations over the last 50 kyr in a currently oligotrophic subtropical region, the Gulf of Cadiz. Data combine refined results from previous investigations on dinocyst assemblages, alkenones, and stable isotopes (18O, 13C) in planktonic (Globigerina bulloides) and endobenthic (Uvigerina mediterranea) foraminifera from cores MD04-2805 CQ and MD99-2339, with new isotopic measurements on epibenthic (Cibicides pachyderma-Cibicidoides wuellerstorfi) foraminifera and dinocyst-based estimates of PP using the new n = 1,968 modern database. We constrain PP variations and export production by integrating qualitative information from bioindicators with dinocyst-based quantitative reconstructions such as PP and seasonal sea surface temperature and information about remineralization from the benthic Δδ13C (difference between epibenthic and endobenthic foraminiferal δ13C signatures). This study also includes new information on alkenone-based SST and total organic carbon which provides insights into the relationship between past regional hydrological activity and PP regime change. We show that PP, carbon export, and remineralization were generally high in the NE subtropical Atlantic Ocean during the last glacial period and that the Last Glacial Maximum (LGM) had lower Δδ13C than the Heinrich Stadials with sustained high PP, likely allowing enhanced carbon sequestration. We link these PP periods to the dynamics of upwelling, active almost year-round during sadials, but restricted to spring-summer during interstadials and LGM, like today. During interstadials, nutrient advection through freshwater inputs during autumn-winter needs also to be considered to fully understand PP regimes.
(Paleoceanography and Paleoclimatology. vol. 37, n° 2572-4525, 01/02/2022)
GEO-OCEAN, UBS, IFREMER, INSU - CNRS, UBO EPE, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, GEOTOP, EPM, UdeM, UQAT, UQAR, UQAM, KOPRI, CCMAR, UAlg, LOCEAN-PROTEO, LOCEAN, MNHN, IRD, INSU - CNRS, SU, CNRS, IPSL (FR_636), ENS-PSL, UVSQ, CEA, INSU - CNRS, X, CNES, SU, CNRS, UPCité
Intergenerational effects of environmentally-aged microplastics on the Crassostrea gigas
(Environmental Pollution. vol. 294, n° 0269-7491, pp. 118600, 01/02/2022)
LIENSs, INSU - CNRS, ULR, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Decadal beach-dune profile monitoring along a 230-km high-energy sandy coast: Aquitaine, southwest France
Large-scale coastal monitoring programs are challenging to maintain over time but are necessary to understand and further predict complex coastal evolution and resilience. The 230 km-long Aquitaine coast is a high-energy meso-macrotidal coast composed of beach-dune systems showing dramatic morphological changes at seasonal and interannual scales. This study investigates the alongshore variability in beach-dune response based on a unique 11-year dataset of 41 spaced transects surveyed yearly in spring. The dataset is completed by interspersed autumn LiDAR surveys for seasonal analysis. Several beach-dune morphological descriptors are developed, such as beach-dune volume, beach width and different shoreline proxies delimiting the intertidal zone, the beach face and the dune face. The Aquitaine beach-dune system is characterised by a north-south gradient, from chronically eroding dunes backing low-elevation dissipative beaches in the north, to slowly accreting dunes backing wide beaches in the south, through a range of intermediate beach-dune states. Time- and spatially-averaged shoreline (dune foot position) trend is −0.5 m/year (erosion), with local variations ranging from −5.9 m/year to +2.1 m/year. During the 2013–2014 winter widespread erosion was observed, with the shoreline eroding by 13 m and 8 m on average along the Gironde and Landes coasts, respectively. This dataset provides insight into the timing, magnitude and spatial variability of beach-dune recovery from the outstandingly erosive 2013–2014 winter. We also show that local beach-dune volume is a good proxy for long-term shoreline trend. It is advocated that such large-scale coastal monitoring by means of single beach profiles spaced and distributed along 10–100 km of coast is a cheap and efficient approach to address coastal changes at regional scale, which can bring complementary information to aerial photographs interpretation to determine long-term shoreline evolution trend and thus contribute to support sustainable coastal management and planning.
(Applied Geography. vol. 139, n° 0143-6228, pp. 102645, 01/02/2022)
BRGM, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, OCNA
Biodiversité et fonctionnement de l’écosystème benthique dans la Vasière Ouest Gironde
Les grands fleuves influencent fortement certaines régions côtières (i.e., les Riverdominated Ocean Margins, ou RiOMar), qui présentent de forts taux de sédimentation et auxquelles sont associés des communautés benthiques et des processus biogéochimiques dont le fonctionnement varie en fonction de la dynamique temporelle des flux particulaires et de leur interaction avec l'hydrodynamisme. La Vasière Ouest-Gironde (VOG) constitue un modèle pertinent pour ce type de systèmes puisqu’elle constitue la principale zone de dépôt primaire des particules issues de l'estuaire de la Gironde, et qu’elle est située dans un environnement hautement énergétique. Bien que sa dynamique sédimentaire ait fait l’objet de nombreux travaux, l’étude des caractéristiques (dont la matière organique associée) des sédiments superficiels, et de la macrofaune benthique y a été jusqu'à présent négligée. L’objectif de cette thèse consiste à mieux décrire la structuration spatio-temporelle de l’écosystème benthique de la VOG, via l’étude de la matière organique particulaire (MOP) sédimentée ainsi que de la composition de la macrofaune benthique et de son activité. Une comparaison a par ailleurs été effectuée avec le prodelta du Rhône qui a déjà beaucoup été étudié. Bien qu’également situé en zone tempérée, celui-ci diffère en effet de la VOG à la fois par la saisonnalité plus marquée des apports fluviaux ainsi que par la plus faible intensité de l'hydrodynamisme dans la zone réceptrice. Une campagne synoptique (juin 2018, 32 stations) et 4 campagnes saisonnières (5 stations le long d’un gradient côte-large, octobre 2016-avril 2018) ont été réalisées sur la VOG dans des conditions de débits et d’hydrodynamisme contrastées. Une large gamme de paramètres a été mesurée : (1) caractéristiques des sédiments superficiels (granulométrie, surfaces spécifiques, descripteurs quantitatifs et qualitatifs de la MOP), (2) composition de la macrofaune, et (3) traces d’activité biologique (imagerie de profils sédimentaires). Sur la base de l’analyse de la distribution spatiale de ces paramètres, les résultats obtenus confirment la subdivision de la VOG en une zone proximale et une zone distale qui avait déjà été mise en évidence par des études sédimentologiques. Ils montrent l’existence de gradients de profondeur (i.e., entre zones proximale et distale et à l’intérieur de la zone distale) marqués pour la plupart de ces paramètres. L’analyse des corrélations entre ces variations spatiales et celles de plusieurs facteurs de contrôle potentiels suggère le rôle prédominant de l’hydrodynamisme comparé à celui du débit de la Gironde et du chalutage de fond. Mes résultats montrent également l’existence de variations temporelles dont la composante saisonnière est liée à l’efflorescence printanière, et à laquelle se superpose une tendance interannuelle entre 2016 et 2018 pour la composition de la macrofaune benthique. Dans le cas de cette dernière, et pour les 3 stations déjà échantillonnées en 2010, mes résultats montrent enfin l’existence d’importants changements temporels entre 2010 et 2016-2018. Ces changements sont attribués à la succession de tempêtes exceptionnelles intervenues durant l’hiver 2013/2014, qui aurait profondément perturbé l’écosystème benthique de la VOG et initié une séquence de cicatrisation. De manière générale, une différence importante avec le prodelta du Rhône réside dans le rôle majeur joué par l’hydrodynamisme (i.e., par rapport aux apports fluviaux) dans le contrôle de la structuration spatio-temporelle des paramètres étudiés. Cette différence tend à valider la transposition aux zones tempérées de la typologie des RiOMar jusqu’ici établie sur des bases biogéochimiques et principalement à partir d’exemples tropicaux et subtropicaux.
(28/01/2022)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS