GDG Environnement

The accurate simulation of sea ice deformation and fracturing remains a significant challenge, driving the development of advanced continuum rheologies. In particular, brittle (elasto-brittle or EB, Maxwell elasto-brittle or MEB, brittle Bingham-Maxwell or BBM) rheologies are a promising advancement, introducing a damage parameter that accounts for sub-grid scale fractures and material degradation under high stresses without requiring large deformations. They simulate realistic large scale fields with adequate heterogeneity and intermittency even at coarser resolution.However, the conventional MEB implementation, which relies on correcting super-critical stresses to bind the simulated stress to the yield criterion, inadvertently introduces a growth of numerical errors in the stress field. These errors can be reduced by introducing the Plante and Tremblay (2021) generalized stress correction scheme.Here, the generalized stress correction scheme is added to the implemenation of the MEB rheology in the sea ice component of the Massachussetts Institute of Technology general circulation model (MITgcm), a community model that also includes a viscous-plastic (VP) rheology.The results of pan-Arctic simulations with different levels of numerical errors in the stress field are compared against simulations using the VP rheology to identify the effect of numerical errors on the deformation behaviour. Our findings reveal three critical insights. First, we find that the generalized correction scheme successfully reduces numerical errors in the stress field in the complex Arctic simulations. Second, we show that reducing the numerical errors effectively reduce the number of simulated Linear Kinematic Features (LKFs). This confirms that numerical errors are partly responsible for the generated spatial heterogeneity in the MEB rheology. Third, we introduce artificial numerical errors to the yield curve of both MEB and VP to find that the MEB rheology is a lot more sensitive to it than the VP rheology. Additionally, we use idealized scenarios to isolate the problem from the complexitiy of an Arctic simulation. In the idealized experiments we can reproduce our results and find that the fracture angle seems to be dependent on the generalized correction scheme, as well.Our work leads to more understanding of the MEB rheology with the goal of finding the source of heterogeneity and the seeding of LKFs in sea ice models.

Abstract The rapid decline of wild populations has resulted in complete extinction of many species. In some cases, this outcome has been avoided through the establishment of ex situ conservation breeding populations. These have the aim of safeguarding the survival of the species and ultimately their reintroduction to the wild. In the case of Partula tree snails, conservation work spanning 4 decades has included ex situ breeding and reintroduction attempts. Most Partula tree snails of French Polynesia are categorized as Extinct on the IUCN Red List as a result of the introduction of invasive predators. Ten species survive only in ex situ conservation breeding centres and reintroduction attempts have been underway since 2015. In 2024, a wild population of Partula tohiveana was located, formed as a result of reintroductions to Moorea Island over the previous decade. This is the first Extinct in the Wild invertebrate species to have been re-established through coordinated, interdisciplinary ex situ and in situ conservation actions.

ABSTRACT Reliable ground-motion measurements are essential for seismic hazard assessment and require seismological stations to be installed in free-field conditions, away from structural interferences. However, global network analyses show diverse installation configurations that can affect measurements. Although topographic effects are natural, their influence can extend over several meters, making them closely related to operators’ installation choices. Although summit effects are well studied and known to cause strong amplifications, the impact of cliffs or escarpments remains less explored. In this study, 16 SmartSolo IGU-16HR 3C nodes were placed on either side of a 30-m cliff located in Cephalonia (western Greece), for 4–10 months, recording 307 low-to-moderate-magnitude seismic events. The main results reveal that de-amplifications recorded at the cliff base are greater than amplifications determined at the cliff top, particularly between 5 and 15 Hz. This study shows that amplification and de-amplification are primarily driven by topography, whereas their directional dependence is likely shaped by both topographic and lithologic factors. Furthermore, the anisotropy related to cliff fracturing interacts with the effects of source back azimuth. Amplification and de-amplification can be correctly predicted using the frequency-scaled curvature (FSC) and illuminated FSC proxies, provided that an exponential functional form is used for determining de-amplifications at the base of near-vertical cliffs. Furthermore, the azimuthal dependence observed, inducing strong de-amplifications depending on the direction observed, seems related more to the anisotropy of geologic formations than to the cliff topography itself. These effects should be considered when using data from stations in similar topographic settings. Neglecting them can bias ground-motion models and underestimate earthquake magnitudes, particularly for stations at the base of cliffs. From these considerations, we strongly recommend installing future seismological stations a few tens of meters away from the bases and ridges of even small cliffs or escarpments.

autorisations d'usage spcifiques.

The water-film that coats cave walls and speleothems is a key player for the regulation of cave microclimate and the control of speleothem growth. In this paper, we demonstrate the capability of a confocal optical sensor to quantitatively measure on-site the rapid variations of water-film thickness when dripping, active condensation, or dryness occur on walls of various caves. Results obtained from a sample of four prehistoric caves and one stalagmite cave from Southwest France, indicate that the measurable thickness of water-films is generally in the 25-70 µm range for cave walls and reaches 200-300 µm on the horizontal plane of active speleothems. The high measurement frequency enables the monitoring of water-film dynamics for a few minutes, especially the tracking of thickness changes triggered by drop dripping and water flow. The optical sensor appears to be a promising tool for the conservation of prehistoric caves facing subsurface warming.

Introduction L’insécurité alimentaire des ménages constitue une préoccupation importante sur le plan de la santé publique et des politiques au Canada et elle touche un nombre toujours croissant de personnes dans cette période d’incertitude économique et d’inflation. L’objectif de cette revue systématique était de faire la synthèse des données probantes sur les interventions axées sur l’alimentation susceptibles de réduire l’insécurité alimentaire des ménages au Canada. Méthodologie Nous avons inclus les études ayant évalué une intervention axée sur l’alimentation susceptible de réduire l’insécurité alimentaire et celles ayant mesuré l’insécurité alimentaire des ménages, qu’il s’agisse de l’objectif principal de l’étude ou non. Quatre bases de données ont été consultées jusqu’en date du 19 février 2025. La sélection à partir du résumé et du texte intégral, l’extraction de données ainsi que l’évaluation des risques de biais et de la qualité des données probantes ont été effectuées de façon indépendante par deux évaluateurs. (PROSPERO n° CRD42021254450). Résultats L’exposition aux programmes de bons alimentaires est susceptible de réduire l’insécurité alimentaire des ménages, mais l’exposition aux programmes de paniers alimentaires, de jardinage communautaire, d’alimentation scolaire, de chasse et pêche et d’aide alimentaire semble avoir un effet mineur ou nul sur cette insécurité. Le taux d’utilisation des banques alimentaires par les ménages en situation d’insécurité alimentaire est parfois faible et il est fonction du degré d’insécurité alimentaire et du groupe de population. Conclusion L’aide alimentaire peut représenter un dernier recours pour les personnes qui ont un besoin urgent d’avoir accès à de la nourriture à court terme (c.‑à‑d. les populations en situation d’itinérance). Cependant, étant donné l’omniprésence de l’insécurité alimentaire des ménages comme marqueur de défavorisation, il est peu probable que les interventions axées sur l’alimentation aient une incidence majeure sur l’insécurité alimentaire de ces ménages dans son ensemble, cette dernière relevant avant tout d’un problème d’ordre économique. Une approche de politique publique globale d’atténuation de l’insécurité alimentaire des ménage est probablement nécessaire.

ABSTRACTIn recent decades, rising industrial demand for palladium (Pd), driven by its unique properties and affordability compared to other noble metals, has increased its environmental release into aquatic systems. This highlights the need to assess its effects on organisms, given the lack of standardized toxicity studies and regulations for this element. This study examines the acute and chronic impacts of Pd exposure on D. magna. Acute lethality was assessed over 48 h at measured Pd concentrations ranging from 2 to 110 μg/L, yielding an LC50 of 52 ± 2 μg/L and an LC10 of 33 ± 3 μg/L. The impact of natural organic matter from the Suwannee River on Pd lethality and bioaccumulation was also examined. No mortality occurred at DOC concentrations of 1, 2, 5, and 8 mg C/L, in contrast with the results obtained at 0.8 mg C/L, which resulted in an LC50 of 74 ± 1 μg/L. Pd bioaccumulation decreased significantly with increasing DOC concentrations compared to controls. After 15 days of chronic exposure, offspring viability significantly declined, with an EC50 of 1 ± 0.1 μg/L, alongside reductions in total broods per D. magna (EC50: 7 ± 2 μg/L). Parental dry weight also decreased significantly, though the timing of the first brood and weight‐normalized oxygen consumption rates remained unaffected across treatments. Parental survival was notably affected, with an LC50 value of 14 ± 2 μg/L. These results emphasize Pd's potential for both lethal and sublethal effects, highlighting the need for environmental standards to protect aquatic life.

Organic fertilizing residuals (OFRs) enhance soil fertility and support sustainable agriculture due to their rich nutrient and organic matter content. However, these materials are increasingly recognized as a significant source of microplastics (MPs) in agricultural soils, raising concerns about the safety of agroecosystems. Therefore, there is an urgent need to develop a reliable workflow for MP analysis in diverse OFRs, given the challenges of extracting small MPs from such organic matter-rich matrices. This study presents an oxidative-alkaline tandem digestion method that achieves an average organic matter (OM) removal efficiency of 93% across various OFRs. In addition, density centrifugation with NaCl and ZnCl2 brines was utilized to recover six microplastic polymers (PP, PVC, PET, PS, PE, and HDPE), achieving a recovery rate of over 95% for large MPs (600μm-4.75mm) and over 83% for small MP-PE beads (38-45μm). Micro-Fourier transform infrared spectroscopy (μ-FTIR) analysis confirmed that digestion and separation steps did not affect MPs' spectral integrity and chemical identification. To validate the workflow, we applied it to analyze MPs in various OFRs from Québec, allowing for the successful detection of 19MP polymers with sizes down to 10-50μm. This workflow can be applied to multiple OFRs to extract, quantify, and characterize MPs. Ultimately, this workflow will facilitate efficient MPs analysis across diverse OFRs, providing essential data for robust risk assessment and better environmental management to mitigate MP pollution from OFR applications in agricultural soils.