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.
(01/09/2026)
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, 01/09/2026)
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, 01/09/2026)
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
(01/09/2026)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, IC2MP [Poitiers], UP, INC-CNRS, CNRS, URVVC, URCA, URCA, CNRS
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, 01/09/2026)
UR EABX, IRSTEA, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Do benthic foraminifera and their geochemical signature from the Celtic margin differentiate the effects of European and Laurentide Ice Sheets meltwaters on the AMOC across Termination 1?
(01/09/2026)
LPG-ANGERS, LPG, UA, UN UFR ST, UN, INSU - CNRS, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, PALEOCEAN, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA
Transient Surf Zone Circulation Induced by Rhythmic Swash Zone at a Reflective Beach
The influence of cuspate swash dynamics on transient surf zone circulation is investigated using both field observation at the low-tide terraced Grand Popo beach and wave-phase resolving numerical simulations. The ability of the model to describing low-tide terrace beach hydrodynamic is tested, and the model is further applied to investigate the role of wave reflection over a rhythmic swash zone pattern on surf zone wave and current. In the numerical simulations, these mechanisms drive higher surf zone irregularities with beach cusps than for an alongshore-uniform swash zone morphology. Rhythmic swash-based reflection generates a standing wave pattern visible in current and wave fields. The positive feedback of reflection on incoming waves drives occasional strong flash rips occurring with different frequencies than individual waves or groups. The so called breakpoint-swash system is thought to pulse with its own temporal characteristics, which depends on wave forcing but also on surf zone terrace and cuspate morphology.
(01/09/2026)
LEGOS, IRD, UT3, Comue de Toulouse, INSU - CNRS, CNES, CNRS, BRGM, FLUMINANCE, IRMAR, UR, INSA Rennes, INSA, ENS Rennes, UR2, CNRS, Institut Agro, IRSTEA, Inria, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, CNRS, UB
Main Ecological Features of Benthic Macrofauna in Mediterranean and Atlantic Intertidal Eelgrass Beds: A Comparative Study
The present study compares the intertidal eelgrass macrofauna in two geographically and ecologically disparate localities (central Mediterranean and eastern Atlantic). Both coastal ecosystems are developed on extensive large mudflats with eelgrass beds, hosting a great diversity of water birds and providing important socioeconomic assets. These two distinct and distant geographical ecosystems are affected by numerous anthropogenic pressures. By reflecting the response of the structure and functioning of benthic communities to climate change, the two eelgrass ecosystems provide a natural laboratory to investigate global warming. The macrobenthic fauna community of Zostera (Zosterella) noltei eelgrass beds was studied by sampling 34 stations in the Kneiss Islands and 48 stations in Arcachon Bay. A total of 148 species are identified in the Kneiss islands and 117 species in Arcachon Bay, but only 23 species are common to both ecosystems. Diversity, abundance and community structure are significantly different between the two study areas, which could be explained by differences between Mediterranean and Atlantic climatic conditions and by anthropic factors (e.g. fishing pressure, pollution, nutrient inputs) affecting each ecosystem. Multidimensional scaling (n-MDS) analysis identifies two distinct geographical station groups on the basis of species and family-level abundance. On the contrary, three assemblages are identified on the basis of trophic groups distributed between the separate ecosystems. In terms of ecological quality status, the Kneiss site appears to have a good ecological condition and hosts a variety of sensitive species. On the other hand, biotic indices indicate that the Arcachon site is moderately perturbed and that the benthic communities are unbalanced. It is expected that the present-day functioning of the Kneiss Islands ecosystem will become typical of the situation in Arcachon Bay in several decades time, with the development of warmer and drier conditions.
(Journal of Marine Biology & Oceanography. vol. 6, pp. 100174, 01/09/2026)
FSS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, M2C, UNICAEN, NU, INSU - CNRS, UNIROUEN, NU, CNRS
On the robustness of near term climate predictability regarding initial state uncertainties
(Climate Dynamics. vol. 48, n° 0930-7575, pp. 353 - 366, 01/09/2026)
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
Holocene sea ice variability driven by wind and polynya efficiency in the Ross Sea
The causes of the recent increase in Antarctic sea ice extent, characterised by large regional contrasts and decadal variations, remain unclear. In the Ross Sea, where such a sea ice increase is reported, 50% of the sea ice is produced within wind-sustained latent-heat polynyas. Combining information from marine diatom records and sea salt sodium and water isotope ice core records, we here document contrasting patterns in sea ice variations between coastal and open sea areas in Western Ross Sea over the current interglacial period. Since about 3600 years before present, an increase in the efficiency of regional latent-heat polynyas resulted in more coastal sea ice, while sea ice extent decreased overall. These past changes coincide with remarkable optima or minima in the abundances of penguins, silverfish and seal remains, confirming the high sensitivity of marine ecosystems to environmental and especially coastal sea ice conditions.
(Nature Communications. vol. 8, n° 2041-1723, pp. 1334, 01/09/2026)
UNISI, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, GLACCIOS, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, UniPi, UniPi, ENEA, UniFI, ENEA