Tracking the turbidity maximum zone in the Loire Estuary (France) based on a long-term, high-resolution and high-frequency monitoring network
A unique dataset of turbidity from 7 years of continuous monitoring at six stations, distributed evenly along a 62-km long transect, is presented to discuss, for the first time, the present-day dynamics of the turbidity maximum zone (TMZ) in the Loire Estuary. This system is considered one of the largest macrotidal, hyper-turbid estuaries of the European coast, mainly as the result of intense engineering works in the last two centuries. Besides accurate TMZ tracking, from tidal to multi-annual time scales, the high temporal and spatial resolution of measurements allows us to address TMZ aspects scarcely reported in the literature on estuarine sedimentary dynamics. In the Loire Estuary, TMZ moves upstream during periods of low discharge and its upstream boundary may reach up to 62 km from the mouth. The TMZ displacement is faster during its downstream flushing by river floods than during its upstream migration by tidal pumping (respectively 1.6 km day-1 and 0.9 km day-1 during 2011). However, the expulsion of the TMZ from the upper reaches requires higher discharge levels than its installation (respective discharge thresholds of 497-1034 m3 s-1 and 300-360 m3 s-1). This is due to the presence of mobile mud remaining after the TMZ presence, as confirmed by clockwise turbidity-discharge hysteresis patterns. While the installation threshold barely varies over years, the expulsion threshold is higher during years with a more concentrated and persistent TMZ. The interannual variability of the TMZ concentration and persistence is explained by the water volume transported during the previous high discharge period and the duration of the low discharge period, respectively, as recently shown for the Gironde Estuary, leading to a better understanding of TMZ features in macrotidal estuaries. The summer-averaged river flow is introduced as a hydrological indicator of the upstream boundary of the TMZ. In the context of global change, these three discharge-based indicators of TMZ behavior provide powerful tools to assess future scenarios.
(CONTINENTAL SHELF RESEARCH. vol. 117, pp. 1-11, 24/04/2026)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, EDF [E.D.F.]
Spatial and temporal patterns of occurrence of three alien hydromedusae, Blackfordia virginica (Mayer, 1910), Nemopsis bachei (Agassiz, 1849) and Maeotias marginata (Modeer, 1791), in the Gironde Estuary (France)
The species composition and seasonal abundance patterns of gelatinous zooplankton are poorly known for many European coastal-zone waters. The seasonal abundance and distribution of the dominant species of hydromedusae along a salinity gradient within the Gironde Estuary, Atlantic coast of France, were evaluated based on monthly surveys, June 2013 to April 2014. The results confirmed the presence of three species considered to be introduced in many coastal ecosystems around the world: Nemopsis bachei (Agassiz, 1849), Blackfordia virginica (Mayer, 1910), and Maeotias marginata (Modeer, 1791). These species were found at salinities ranging from 0 to 22.9 and temperatures ranging from 14.5 to 26.6 ºC, demonstrating their tolerance to a wide range of estuarine environmental conditions. There was a clear succession of the three species that was influenced by temperature and salinity. Blackfordia virginica was the dominant hydromedusae during the warmest months and occurred at very high abundance (up to 634 individuals.m-3 corresponding to 21.40 g.m-3 as wet weight). The seasonal evolution of the size distribution indicated an extended period of release of medusae by hydroid polyps, and rapid growth, covering the whole period of occurrence for B. virginica. Nemopsis bachei also was present during the warmer months but only locally common. In contrast, Maeotias marginata only occurred in low numbers during autumn and had not been previously detected in the Gironde Estuary. Non-native jellyfishes clearly represent a prominent component of the Gironde Estuary, and additional work is needed to understand the potential impacts on the structure and functioning of entire zooplankton community.
(Aquatic Invasions. vol. 11, n° 1798-6540, pp. 397-409, 24/04/2026)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, UR EABX, IRSTEA, EDF R&D LNHE, EDF R&D, EDF [E.D.F.]
Is herbicide toxicity on micro-algae influenced by the natural Dissolved Organic Matter (DOM)?
Les microalgues, en tant que producteurs primaires, sont à la base des réseaux trophiques aquatiques : elles peuvent donc être directement impactées par les herbicides. Dans l’environnement aquatique, la matière organique dissoute (MOD) peut également influencer les microalgues. La présente étude avait pour but d’étudier l’impact de la MOD naturelle (provenant du Bassin d’Arcachon) sur la toxicité de trois herbicides (irgarol (I), diuron (D) et S-métolachlore (S)), seuls et en mélange, pour deux micro-algues marines: Chaetoceros calcitrans (Cc) et Tetraselmis suecica (Ts), en cultures monospécifiques en laboratoire. Après une exposition de six jours à chaque herbicide (I0,05 et I0,5 µg.L-1; D0,05 et D0,5 µg.L-1; S0,5 et S5 µg.L-1) et à deux mélanges (M1: I0,05+D0,05+S0,5 et M2: I0,5+D0,5+S5), en présence ou non de MOD, les effets ont été évalués sur la croissance, l’efficacité photosynthétique, la quantité relative d’espèces réactives de l’oxygène et le contenu lipidique relatif. En l’absence de MOD, les conditions I0,5 et M2 ont significativement affecté les deux espèces : inhibition de la croissance et de l’efficacité photosynthétique et diminution du contenu lipidique relatif. Les impacts de M2 sur Cc ont été similaires aux effets induits par I0,5 ; en revanche pour Ts, la toxicité de M2 a été supérieure, suggérant une probable synergie entre les molécules. En présence de MOD, des effets significatifs de I0,5 et M2 ont également été observés sur les deux espèces : alors que les effets ont été amoindris en présence de MOD chez Cc, ils ont été amplifiés chez Ts. La présence de MOD naturelle a donc influencé la toxicité des herbicides de façon opposée chez les deux espèces. Ces résultats peuvent être expliqués partiellement par la complexation entre la MOD et les herbicides. En effet, des études ont montré que la MOD pouvait moduler la biodisponibilité des pesticides et des métaux selon la capacité des microalgues à pouvoir réaliser ou non de l’hétérotrophie (mécanisme favorisant la pénétration des molécules dans les cellules). Les variations de toxicité observées dans cette étude pourront être interprétées plus précisément avec les résultats des analyses chimiques en cours d’acquisition (MOD, herbicides et carbone organique dissous).
(pp. 26, 24/04/2026)
UR EABX, IRSTEA, IFREMER, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Integration of contamination peaks with variable intensity and duration by the Polar Organic Chemical Integrative Sampler
Nowadays, pesticides, considering their efficiency on animal and plant parasites, represent considerable progress in food resources management and public health improvement. However, due to intensive use, the three environment compartments (water, air, soil) are contaminated with worrying consequences for human being and ecosystem. In order to conserve and restore the condition of aquatic environments, the European Water Framework Directive (WFD) was adopted in 2000 by the European Union. Indeed, monitoring networks - such as Water Agencies - proceed to regular monitoring, performing spot water sampling up to 12 times a year. But, there are still questions about the spatial and temporal representativeness of this type of sampling. Actually, contamination level in rivers can vary abruptly, depending on season and hydrology at the sampling moment. Thus, contamination peaks could be undetected by monitoring networks, generating a partial snapshot and then estimation of water quality. Passive sampling techniques are proposed and developed to obtain better representativeness of the contamination level, providing average concentration over time with integration of peculiar events like contamination peaks. In this study, the Polar Organic Chemical Integrative Sampler (POCIS) with different king of membranes was considered. This tool, widely used for polar pesticides sampling (0 < log Kow < 4) (Alvarez et al. 2004), allows pre-concentration in situ of analytes and presents an integrative capacity over several week. Its scope and its technical limitations are actually well documented (Lissalde et al. 2011). Furthermore, it was proved that this device may integrate contamination peaks relatively prolonged (about 3 days) for moderately polar compounds (log Kow = 2-3) (Mazzella et al. 2008). Concerning shorter contamination peaks (few hours-few days) generated by punctual pollutions, interrogations about its reactivity (e.g. lag time) is still remaining. This study aimed to show the POCIS reactivity for three different contamination peak patterns, with variable intensity and duration, over a total exposure period of 14 days. For this experimentation under laboratory controlled conditions, fifteen pesticides covering different polarities (log Kow=0-5) and groups (herbicides, fungicides, insecticides) were selected. The data showed different accumulation kinetic profiles, depending on physico-chemical characteristics of the substances and the exposition duration. Some compounds presented a lag effect, or on the contrary a burst effect. For seven compounds, POCIS sampled correctly contamination peaks, which show the ability of this device to sample fleeting events.
(pp. 39, 24/04/2026)
UR EABX, IRSTEA, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Un projet intégratif en vue de protéger la qualité des eaux face aux usages de pesticides dans le vignoble Bordelais
Présentation du projet intégratif "PhytoCOTE" du LabEx COTE de l'Université de Bordeaux (coordination générale : Francis Macary) à la délégation mexicaine de scientifiques spécialisés sur la question de la protection de l'eau dans la zone métropolitaine de Léon.
(pp. 20, 24/04/2026)
UR ETBX, IRSTEA, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Spatio-temporal dynamics of per and polyfluoroalkyl substances (PFASs) and transfer to periphytic biofilm in an urban river: case-study on the River Seine
Abstract This study addresses the spatio-temporal dynamics of per and polyfluoroalkyl substances (PFASs) in a highly urbanized freshwater hydrosystem, the Seine River (NW France). The distribution of PFASs between water, sediment, and periphytic biofilm was investigated at three sampling sites along a longitudinal gradient upstream and downstream from the Paris urban area. Seasonal variability was assessed through four sampling campaigns performed under contrasting hydrological conditions. In the dissolved phase, ∑PFASs fluctuated between 2 and 9 ng L−1 upstream and 6–105 ng L−1 downstream from Paris. Negative correlations between dissolved PFAS levels and river flow rate were generally observed, corroborating the predominance of point-source PFAS inputs at these sites. 18/19 target PFASs were detected, with a predominance of PFHxS and PFOS (20% of ∑PFASs each), except for the farthest downstream site where 6:2 FTSA was prevalent (35 ± 8% of ∑PFASs), likely reflecting industrial and urban inputs. In biofilms, ∑PFASs fell in the 4–32 ng g−1 dw range, and substantial bioconcentration factors (BCFs) were reported for PFNA, PFDA, and PFOS (log BCF 2.1–4.3), higher than those of PFHxS or PFOA. BCFs varied inversely with dissolved PFAS levels, potentially pointing to concentration-dependent bioaccumulation. Biofilm community characteristics (C/N ratio) may also be an influential determinant of PFAS bioaccumulation.
(Environmental Science and Pollution Research. vol. 25, n° 0944-1344, pp. 1-9, 24/04/2026)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, UR HBAN, IRSTEA
Ideas and perspectives : Southwestern tropical Atlantic coral growth response to atmospheric circulation changes induced by ozone depletion in Antarctica
Recent Southern Hemisphere (SH) atmospheric circulation, predominantly driven by stratospheric ozone depletion over Antarctica, has caused changes in climate across the extratropics. Here, we present evidence that the Brazilian coast (southwestern Atlantic) may have been impacted from both wind and sea-surface temperature changes derived from this process. Skeleton analysis of massive coral species living in shallow waters off Brazil are very sensitive to air–sea interactions, and seem to record this impact. Growth rates of Brazilian corals show a trend reversal that fits the ozone depletion evolution, confirming that ozone impacts are far reaching and potentially affect coastal ecosystems in tropical environments.
(Biogeosciences Discussions. vol. 12, n° 1810-6277, pp. 13193-13213, 24/04/2026)
LARAMG, UERJ, USP, BTP, LOCEAN, IPSL, ENS-PSL, UVSQ, UPMC, CEA, INSU - CNRS, X, CNES, CNRS, MNHN, IRD, UPMC, INSU - CNRS, CNRS, Departamento de Geoquímica, UFF, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, NTU, IRD [Ile-de-France]
Study of benthic foraminiferal faunas along the French Mediterranean coasts: a new biotic index in the EU Water Framework Directive
(24/04/2026)
LPG-ANGERS, LPG, UA, UN UFR ST, UN, INSU - CNRS, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Spatial distribution of living (Rose Bengal stained) benthic foraminifera in the Loire estuary (western France)
Ninety-seven surface sediment samples were collected in September 2012 from intertidal and subtidal areas along the Loire estuary (western France). The main objective of this work is to study the spatial distributional patterns of living benthic foraminifera and their link to the environmental parameters (distance to sea, elevation, grain size, total organic carbon, trace metals, sedimentary carbonates, and polycyclic aromatic hydrocarbons) in the Loire estuary. Foraminiferal analysis was also extended to the dead assemblages in thirty-three surface samples from the lower inner estuary. The highest absolute densities of living benthic foraminifera are found in the lower inner estuary within the polyhaline domain. This is attributed to the presence of mudflats with abundant food source, i.e. microphytobenthos. The low densities found in the outer estuary (euhaline domain) are attributed partly to the sandy nature of the sediments and the food source inhabiting this substrate. The near absence of foraminifera in the inner estuary (mesohaline and polyhaline domains) is inferred to the physical disturbance resulting from the regular dredging of the navigation channel. The living assemblages are dominated by three typical estuarine species: Ammonia tepida and Haynesina germanica in the intertidal mudflats of the lower inner estuary and Cribroelphidium excavatum in the sandy subtidal sediments of the lower inner and outer estuary. In the Loire estuary, H. germanica has an unusual intermediate geographical distribution along the estuary between A. tepida and C. excavatum while in most temperate estuaries this species is present upstream in the mesohaline domain. This is most likely the result of the regular dredging of the navigation channel damaging its natural habitat. This might be also the explanation for the total absence of agglutinated species usually dominating the oligohaline domain. The canonical correspondence analysis shows that elevation (and its link to time of emersion), distance to sea (and its correspondence with salinity), and organic carbon content appear to be the primary drivers of foraminiferal distribution. The present study provides for the first time ecological and distribution patterns of living benthic foraminiferal communities in the Loire estuary. This baseline knowledge is necessary for the future studies focusing on the use of benthic foraminifera as bio-indicators in the Loire estuary and in transitional environments in general.
(Journal of Sea Research (JSR). vol. 118, n° 1385-1101, pp. 1-16, 24/04/2026)
BIAF, UA, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, LETG-Angers, LETG, UNICAEN, NU, UA, EPHE, PSL, UBO EPE, UR2, CNRS, IGARUN, UN
Ideas and perspectives: Southwestern tropical Atlantic coral growth response to atmospheric circulation changes induced by ozone depletion in Antarctica
Recent Southern Hemisphere (SH) atmospheric circulation, predominantly driven by stratospheric ozone depletion over Antarctica, has caused changes in climate across the extratropics. Here, we present evidence that the Brazilian coast (southwestern Atlantic) may have been impacted from both wind and sea-surface temperature changes derived from this process. Skeleton analysis of massive coral species living in shallow waters off Brazil are very sensitive to air–sea interactions, and seem to record this impact. Growth rates of Brazilian corals show a trend reversal that fits the ozone depletion evolution, confirming that ozone impacts are far reaching and potentially affect coastal ecosystems in tropical environments.
(Biogeosciences. vol. 13, n° 1726-4170, pp. 2379-2386, 24/04/2026)
LARAMG, UERJ, USP, BTP, LOCEAN, IPSL, ENS-PSL, UVSQ, UPMC, CEA, INSU - CNRS, X, CNES, CNRS, MNHN, IRD, UPMC, INSU - CNRS, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, NTU