The role of natural hazards and human activities on change of sedimentation patterns: The case of Lake Yamanaka (Fuji Five Lakes, Japan)
The last eruption of Mt Fuji (Japan) occurred in A.D. 1707. The eruption lasted 16 days from 16 December 1707 to 1 January 1708 (Tsuya, 1955) and 1.8 km3 of volcanic materials were ejected in total (Miyaji et al., 2011). Lake Yamanaka, a very shallow lake (max. 14. 3 m depth) located at the foot of the east-north-eastern flank of Mt Fuji, was heavily impacted by the eruption. A thick scoria layer entirely covered the catchment of Lake Yamanaka. The thickness of the deposit varies from 5 to 37 cm around Lake Yamanaka and reaches up to 149 cm at the south-west extremity of the catchment (Miyaji et al., 2011). In order to study the influence of Hoei eruption on Lake Yamanaka, 5 gravity cores were taken during the 2014 QuakeRecNankai campaign. The Hoei scoria was present at the bottom of the one core and in the core catcher of the four other cores. High resolution magnetic susceptibility, XRD, XRF, LOI, C/N and 210Pb/137Cs analyses were performed on the gravity cores. The results shows three distinct periods of sedimentation: (1) From Hoei eruption to A.D. 1900; (2) From A.D. 1900 to A.D. 1990; (3) From A.D. 1990 to A.D. 2014. The first period is characterized by a very low sedimentation rate (~0.07 cm/yr). During this period, the sediments of the catchment were trapped below the thick Hoei scoria layer. However, peaks of terrigenous input are recorded. We link such detrical signals with violent typhoons that hit the Fuji Five Lakes region. The water from the heavy rains percolated through the porous thick scoria layer and saturated it. As a result, surface runoffs carried the sediments from the catchment into Lake Yamanaka. The second period (from A.D. 1900 to A.D. 1990) is defined by an increase of the sedimentation rate (~0.16 cm/yr). The development of soil and the agriculture (e.g. pastureland, rice field, mulberry plantations) reduced the impact of Hoei scoria. The terrigenous inputs are higher than previously but remained more or less constant during this period of time. As the thickness of the scoria layer is partially reduced or covered by new soil, rains triggered by smaller typhoons could drain the sediments from watershed and transport them into the lake. The most recent period representing the last 27 years is characterized by a very high sedimentation rate (~1.036 cm/yr). The transition between period 2 and period 3 corresponds to the development of mass tourism and the urbanization around Lake Yamanaka. It is marked by an increasing of atmospheric pollution (Pb, Zn). In the upper part of the cores, a peak of 137Cs is observed. Such peak is related to cesium fall-out after Fukushima incident in 2011. In addition to the fingerprint of human impact, the lake also record a terrigenous signal related to the 2007 Fitow typhoon which provoked damage in the area. This study highlights the influence of eruptions and typhoons on the sedimentation of Lake Yamanaka. In the present day, the sedimentation recovery after a major eruption is accelerated by human activity.
(21/06/2026)
ULiège, ULiège, AGEs, ULiège, UEC, EDYTEM, USMB [Université de Savoie] [Université de Chambéry], CNRS, Fédération OSUG, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, ULiège, AORI, UTokyo, UGent, UGent
Atmospheric Corrections and Multi-Conditional Algorithm for Multi-Sensor Remote Sensing of Suspended Particulate Matter in Low-to-High Turbidity Levels Coastal Waters
The accurate measurement of suspended particulate matter (SPM) concentrations in coastal waters is of crucial importance for ecosystem studies, sediment transport monitoring, and assessment of anthropogenic impacts in the coastal ocean. Ocean color remote sensing is an efficient tool to monitor SPM spatio-temporal variability in coastal waters. However, near-shore satellite images are complex to correct for atmospheric effects due to the proximity of land and to the high level of reflectance caused by high SPM concentrations in the visible and near-infrared spectral regions. The water reflectance signal ((w)) tends to saturate at short visible wavelengths when the SPM concentration increases. Using a comprehensive dataset of high-resolution satellite imagery and in situ SPM and water reflectance data, this study presents (i) an assessment of existing atmospheric correction (AC) algorithms developed for turbid coastal waters; and (ii) a switching method that automatically selects the most sensitive SPM vs. (w) relationship, to avoid saturation effects when computing the SPM concentration. The approach is applied to satellite data acquired by three medium-high spatial resolution sensors (Landsat-8/Operational Land Imager, National Polar-Orbiting Partnership/Visible Infrared Imaging Radiometer Suite and Aqua/Moderate Resolution Imaging Spectrometer) to map the SPM concentration in some of the most turbid areas of the European coastal ocean, namely the Gironde and Loire estuaries as well as Bourgneuf Bay on the French Atlantic coast. For all three sensors, AC methods based on the use of short-wave infrared (SWIR) spectral bands were tested, and the consistency of the retrieved water reflectance was examined along transects from low- to high-turbidity waters. For OLI data, we also compared a SWIR-based AC (ACOLITE) with a method based on multi-temporal analyses of atmospheric constituents (MACCS). For the selected scenes, the ACOLITE-MACCS difference was lower than 7%. Despite some inaccuracies in (w) retrieval, we demonstrate that the SPM concentration can be reliably estimated using OLI, MODIS and VIIRS, regardless of their differences in spatial and spectral resolutions. Match-ups between the OLI-derived SPM concentration and autonomous field measurements from the Loire and Gironde estuaries' monitoring networks provided satisfactory results. The multi-sensor approach together with the multi-conditional algorithm presented here can be applied to the latest generation of ocean color sensors (namely Sentinel2/MSI and Sentinel3/OLCI) to study SPM dynamics in the coastal ocean at higher spatial and temporal resolutions.
(Remote Sensing. vol. 9, n° 2072-4292, 21/06/2026)
LOV, OOVM, UPMC, INSU - CNRS, CNRS, UPMC, INSU - CNRS, CNRS, MIO, IRD, AMU, INSU - CNRS, UTLN, CNRS, IRSNB / RBINS, UB, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, MMS, UM, UN UFR ST, UN, UFR SPB, UN
Natural dissolved organic matter decreases toxic effects of herbicide mixtures towards freshwater microalgae
As primary producers, microalgae are the basis of aquatic food webs. Thus, they can be directly impacted by herbicides which are, in turn, affected by complex and changing conditions of freshwater environments. For instance, dissolved organic matter (DOM) may interact with pesticides and affect their fate and ecotoxicity. Therefore, the present study aimed to investigate whether the natural DOM influences the toxicity of herbicide mixtures towards two freshwater microalgae. To that aim, a diatom (Gomphonema gracile) and a chlorophyte (Sphaerellopsis sp.) isolated from a pristine river were exposed to a mixture of three herbicides, with or without natural DOM. Herbicide concentrations were selected to represent environmentally realistic conditions (0.05µg/L for irgarol and diuron, 0.5µg/L for metolachlor) and a 10-times higher exposure. The responses of the microalgae were assessed over a growth cycle, by monitoring daily their growth and photosynthetic efficiency. On the last day, the intracellular relative lipid content was quantified, as well as the proportion of bacteria in the microcosms to ensure no bloom had occurred. In the absence of DOM, photosynthetic activity decreased in Sphaerellopsis at both concentrations of herbicides, whereas Gomphonema was only impacted at the highest one. DOM alone had no influence on the parameters measured for Gomphonema, but significantly stimulated the growth of Sphaerellopsis. Surprisingly, combined exposure to DOM and herbicides removed the toxic impacts observed without DOM for both species. Our results demonstrate species-specific responses to DOM and herbicides, and highlight a mitigation of pesticides impacts towards microalgae in the presence of natural DOM.
(pp. 21, 21/06/2026)
UR EABX, IRSTEA, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, IFREMER
Enjeux environnementaux et sanitaires associés aux pesticides : de leur usage à leur dispersion dans l’environnement en lien avec leur impact
(21/06/2026)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, IC2MP [Poitiers], UP, INC-CNRS, CNRS, URVVC, URCA, URCA, CNRS
Fragilariopsis kerguelensis size variability from the Indian subtropical Southern Ocean over the last 42 000 years
In the open Southern Ocean (SO), both modern and past size changes of the diatom Fragilariopsis kerguelensis appear to be strongly controlled by iron availability. Conversely, sea surface temperatures (SST) and sea ice seasonal dynamics take over in the seasonal sea-ice zone where iron is not limiting. No information exists on F. kerguelensis biometry from the subtropical SO, on the other extreme of the thermal and nutrient gradients. We present here new data on mean valve area of F. kerguelensis (FkergArea) from a sediment core covering the last ~ 42 cal kyrs from the southern Subtropical Front (SSTF) of the Indian sector of the SO, where iron and silica stocks are thought to have been consistently low over this period. Our results suggest that larger F. kerguelensis valves occurred during the Last Glacial period, and declined during the Holocene period. These findings indicate that more favourable SST, within the F. kerguelensis ecological range, during the Last Glacial period may have enabled F. kerguelensis to make better use of the low silica stocks prevailing in the subtropical zone leading to larger valves. Conversely, declining FkergArea during the deglacial and the Holocene periods may have been a result of higher SST which hampered the utilization of silica.
(Antarctic Science. vol. 29, n° 0954-1020, pp. 139-146, 21/06/2026)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
On the robustness of near term climate predictability regarding initial state uncertainties
(Climate Dynamics. vol. 48, n° 0930-7575, pp. 353 - 366, 21/06/2026)
LOCEAN, IPSL, ENS-PSL, PSL, UVSQ, UPMC, CEA, INSU - CNRS, X, IP Paris, CNES, CNRS, MNHN, IRD, UPMC, INSU - CNRS, CNRS, NOC, CEP, UNIBE, OCCR, UNIBE, PARVATI, 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
Proposition de concentrations de références en mercure dans l'ichtyofaune de Guyane
La pollution des écosystèmes aquatiques par le mercure est un problème majeur de la Guyane française, soumis à l'orpaillage illégal intensif depuis de nombreuses années. Au niveau européen, une norme de qualité environnementale pour le biote (NQEbiote : 0,02 mg Hg.kg-1 poids frais) a été définie dans le cadre de la directive cadre sur l'eau (DCE). Ce rapport a pour but d'aider à la mise en place de la NQEbiote en Guyane française par : 1/ si possible, l'identification de sites non pollués par le mercure d'origine anthropique ; 2/ la détermination de concentrations de références en mercure pour l'ichtyofaune associées à ces sites ; 3/ l'identification d'espèces de poissons sentinelles potentielles de cette pollution. Une base de données d'environ 9000 poissons (3000 pour les criques et 6000 pour les fleuves) a été constituée à partir des résultats des programmes de recherche et de surveillance depuis 1993. Les concentrations en mercure mesurées dans le muscle de ces poissons se révèlent presque toujours supérieures à la NQEbiote (100% pour les criques et 89 % pour les fleuves). Peu de zones de références potentielles ont été identifiées sur plus de 200 stations échantillonnées. Ainsi pour les criques, 7 stations réparties sur 6 bassins versants différents présentent des concentrations significativement plus faibles que les autres stations. Sur les fleuves, seulement 2 zones (groupe de stations) ont été identifiées comme références potentielles sur le bassin versant de l'Oyapock. L'analyse de ces données a permis de proposer plusieurs espèces sentinelles, c'est à dire intégratives d'une contamination mercurielle. Pour les criques, il s'agit de Copella carsevennensis, Pyrrhulina filamentosa, Jupiaba (abramoides et keithi), Moenkhausia oligolepis, Pimelodella (cristata, geryi et macturki), Gymnotus carapo et Sternopygus macrurus. Pour les fleuves, 3 genres et espèces ont été retenus : Ageneiosus inermis, Acestrorhynchus (falcatus et microlepis) et Hoplias aïmara. Des recommandations opérationnelles sont proposées pour le suivi de la DCE telles que : i/ échantillonner moins de stations (en privilégiant celles suivies par l'OMS), ii/ espacer la fréquence des suivis (tous les 2 ans), iii/ mais, en contrepartie, augmenter l'effort de pêche sur les espèces sentinelles proposées.
(pp. 78, 21/06/2026)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, UR MALY, IRSTEA
How does climate change make fish late for dinner?
Imagine you are a young and hungry fish looking for food in an estuary (the part of a river where it meets the ocean). You need to grow big and strong before you migrate to the ocean, and depend on tiny floating creatures (plankton) for food. However, the occurrence of these tiny creatures in the estuary varies seasonally. Lucky for you, nature has synchronized both your time in the estuary and that of your prey, and you survive. This synchronization depends on many different factors, among them the temperature of the water. Now imagine someone turning up the heat (like we humans are doing by changing the climate). Could the rising water temperatures mess up the timing for you, the predator, and your prey? To answer this question we looked at climate related changes in the synchronization of predator and prey in the biggest estuary in Western Europe. And indeed, we found signs of temporal mismatches in its aquatic food web. We fear that the observed changes can put this important ecosystem and its role as a big fish nursery at risk.
(Environmental Science Journal for Teens, pp. 5, 21/06/2026)
UR EABX, IRSTEA, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Utilisation des échantillonneurs passifs pour évaluer la contamination des écosystèmes aquatiques par les produits phytosanitaires - Application à un bassin versant viticole
L'échantillonnage passif représente une alternative aux prélèvements ponctuels pour la détermination de la contamination en pesticides. Les échantillonneurs présentent l'avantage d'intégrer la contamination du milieu pendant la période d'exposition de l'outil et permettent un abaissement des limites de détection grâce à l'accumulation des substances. Parmi les outils existants, les échantillonneurs passifs intégratifs pour les contaminants organiques polaires (POCIS : Polar Organic Chemical Integrative Samplers) ont été utilisés avec succès pour évaluer la contamination des hydrosystèmes en contexte agricole [1]. Ces POCIS peuvent être adaptés pour permettre la surveillance de milieux exigus ou de milieux à écoulements épisodiques tels que les fossés agricoles. Ces adaptations consistent à modifier les dimensions de l'outil, la surface membranaire, la quantité de phase ou encore la porosité des membranes pour influencer la quantité de substances accumulées [2]. Le projet de recherche multidisciplinaire PhytoCOTE étudie l'usage des pesticides dans les agrosystèmes, leurs transferts dans les écosystèmes connexes, leur bioaccumulation, et leur toxicité potentielle chez les organismes aquatiques. Le site d'étude est localisé dans une zone d'exploitation viticole sur la rive droite de l'estuaire de la Gironde. Dans ce cadre, un suivi annuel de la variabilité spatio-temporelle des concentrations en pesticides a été mis en place. Le suivi des cours d'eau permanents (ordre 1, 2 et 3) repose sur le déploiement de POCIS classiques à une fréquence mensuelle. Le suivi des fossés repose sur le déploiement de POCIS adaptés (miniPOCIS et POCIS-T) pendant la période d'application des pesticides. Parallèlement, des prélèvements d'eau sont réalisés à une fréquence mensuelle ou bimensuelle. Le suivi de la contamination est basé sur une liste de plus de 200 substances parmi lesquels les pesticides utilisés sur le bassin versant (54 substances). Différentes techniques d'extraction et d'analyse par LC-MS/MS et GC-MS/MS ont été développées pour permettre la quantification de ces composés.
(pp. 2, 21/06/2026)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, UR ETBX, IRSTEA
Shoreline resilience to individual storms and storm clusters on a meso-macrotidal barred beach
This study investigates the impact of individual storms and storm clusters on shoreline recovery for the meso-to macrotidal, barred Biscarrosse beach in SW France, using 6 years of daily video observations. While the study area experienced 60 storms during the 6-year study period, only 36 storms were analysed due to gaps in the video data. Based on the 36 individual storms and 13 storm clusters analysed, our results show that clustering impact is cumulatively weak and shoreline retreat is governed by the first storms in clusters, while the impact of subsequent events is less pronounced. The average post-storm beach recovery period at this site is 9 days, consistent with observations at other beaches. Apart from the dominant effect of present storm conditions, shoreline dynamics are also significantly affected by previous storm influence, while recovery is strongly modulated by tidal range and the bar location. Our results reveal that not only is the storm energy important but also the frequency of recurrence (storms result in greater retreat when time intervals between them are longer), which suggests an interaction between short storm events and longer-term evolution.
(Geomorphology. vol. 290, n° 0169-555X, pp. 265-276, 21/06/2026)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, LEGOS, IRD, UT3, Comue de Toulouse, INSU - CNRS, CNES, CNRS