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Étude expérimentale du comportement d’une géomembrane en PVC sous différents modes de chargement en traction
No full textInternational audienceGeomembrane are not meant to support mechanical actions, however, one of the main causes of the malfunctioning of their waterproofing properties is attributed to the unexpected tensile forces that may be generated during its service life, and that may potentially lead to failure. Driven by this meticulous problem, this study focuses on characterizing the tensile behaviour of Polyvinyl Chloride geomembranes by evaluating their failure criteria in terms of resistance and elongation. A wide range of tensile loading rates was applied to investigate the rate-dependent effects on the material’s ultimate properties. Additionally, complementary long-term (creep) tests were conducted to examine the impact of the loading weight on the failure thresholds. Based on these results, this study proves that creep behaviour can be predicted through tensile tests, provided the environmental conditions remain constant. The results highlight the important role of the loading rates on the GM performance, providing a solid base for engineering design
Double-structured zinc oxide nanowire architecture for robust superhydrophobicity and multifunctionality
No full textInternational audienceSuperhydrophobic surfaces have received tremendous interest for non-wetting applications such as self-cleaning, anti-icing, anti-bacterial, and anti-corrosion devices; however, the degradation of this superhydrophobicity, both over time and after exposure to various harsh environmental conditions, remains a major barrier to their widespread adoption. Here, we propose a scalable and low-cost method for developing robust superhydrophobic films with micro/nano open-porous structures. These films consist of double-structured zinc oxide nanowire vertical networks (DS ZnO NW) achieved through a wet chemical route and non-fluorinated grafting with hexadecyl trimethoxysilane. The surface exhibits remarkable superhydrophobicity, as evidenced by non-adhesive water droplets even on flat substrates. Additionally, the long-term stability of superhydrophobicity is proven as a water contact angle greater than 150° was retained even after a period of 28 days both at ambient conditions as well as after exposure to various harsh conditions including water immersion, high pressure, high humidity, strong base, and low temperature. The DS ZnO NWs developed here offer long-lasting superhydrophobicity without fluorination, positioning them as promising candidates for integration into a wide range of next-generation devices
Massive Mg-rich fluid release across the brucite + serpentine reaction in subduction zones
No full textInternational audienceIn subduction zones, serpentinized oceanic mantle is expected to dehydrate above 600 °C due to antigorite breakdown (Atg-out reaction). Analysis of compilatory bulk composition of serpentinites shows that brucite (Brc) should also be an important hydrous component, capable of carrying water to depth. The Atg + Brc = Ol + H2O reaction (R1) which occurs at lower temperature than Atg-out, is thus highly relevant for fluid release in subduction zones. Depending on the initial composition of the serpentinized mantle, R1 can produce more water than the Atg-out reaction. The consideration of most recent thermochemical data for brucite and serpentine solid-solutions shows that the R1 reaction proceeds in a narrow temperature range (< 10 °C), implying relatively high dehydration rates. Thermochemical modeling also shows that the fluid released during R1 is highly magnesian ([Mg]/[Si] > 100), i.e., likely to promote Mg metasomatism. In parallel, metamorphic olivine veins formed according to R1 in the Zermatt-Saas meta-ophiolite were examined. They are interpreted as magnesium-rich segregations resulting from the interaction between an Mg-rich fluid and the host serpentinite for around a hundred years. Furthermore, they are crosscut by brucite veinlets formed at R1 conditions or higher, which confirms, in agreement with thermodynamical modeling, that R1 is not a brucite-out reaction. Finally, P-T conditions of R1 were found to coincide with the location of Low Frequency Earthquakes recorded in the Mexican, Nankai and Cascadian subductions; this indirectly supports the role played by R1 as a significant source of fluid in subduction zones
Wild and domesticated animal abundance is associated with greater late-Holocene alpine plant diversity
No full textInternational audienceIn the face of human land use and climate dynamics, it is essential to know the key drivers of plant species diversity in montane regions. However, the relative roles of climate and ungulates in alpine ecosystem change is an open question. Neither observational data nor traditional palaeoecological data have the power to resolve this issue over decadal to centennial timescales, but sedimentary ancient DNA ( sed aDNA) does. Here we record 603 plant taxa, as well as 5 wild, and 6 domesticated mammals from 14 lake sediment records over the last 14,000 years in the European Alps. Sheep were the first domesticated animals detected (at 5.8 ka), with cattle appearing at the early Bronze Age (4.2 ka) and goats arriving later (3.5 ka). While sheep had an impact similar to wild ungulates, cattle have been associated with increased plant diversity over the last 2 ka by promoting the diversity of forbs and graminoids. Modelling of the sed aDNA data revealed a significantly larger effect of cattle and wild ungulates than temperature on plant diversity. Our findings highlight the significant alteration of alpine vegetation and the entire ecosystem in the Alps by wild and domesticated herbivores. This study has immediate implications for the maintenance and management of high plant species diversity in the face of ongoing anthropogenic changes in the land use of montane regions
EPR Dating of Clay Minerals Formation Through Geological Times: Benchmarking From the Quaternary to the Neoproterozoic Era
No full textInternational audienceRevealing the environment and timing of clay formation in the geosphere is of major importance to understand and model the evolution of geological systems at the surface or near-surface of the continents, such as weathering covers, sedimentary basins or hydrothermal systems. Dating clay minerals by electron paramagnetic resonance spectroscopy (EPR) is a promising method that relies on the measurement of stable radiation-induced defects (RIDs) accumulating in their structure over time due to natural radioactivity. This approach has not yet been challenged by the inter-comparison with other geochronological methods, mostly because clay minerals accurately dated with methods independent from the EPR approach and also suitable for the EPR dating remain scarce in the geological record. Herein, an up-to-date protocol for the EPR dating and benchmarking are provided and developed by analyzing selected clay samples. The series includes a Mesoproterozoic illite (Thelon Basin, Canada), two paleosol kaolinites (Ukraine, Estonia) from at least late Ediacaran period, an Ypresian sedimentary kaolinite from the Aquitan Basin (France) and two Miocene and Pliocene kaolinites from lateritic duricrusts (Amazonia, Brazil). Despite some discussed uncertainties mainly related to the Th distribution in the samples, the time variation of dose rate and the thermal history of some clay samples, the EPR ages show a trend close to the 1/1 line with ages determined by other dating methods. These results bring promising support to the EPR dating methodology of clay minerals and extend its potential application field over a time-range spanning from Quaternary to Proterozoic
Experimental Evidence for the Desynchronization of Ecosystem Dynamics by Global Change
No full textInternational audienceAnticipating ecosystem responses to global change requires identifying the isolated and combined effects of environmental disturbance across both space and time. Examining the coordinated responses of ecosystems has recently emerged as a powerful approach to advance this understanding. We conducted two complementary experiments to identify whether, and if so how, warming temperatures, nutrient enrichment, predator overexploitation (i.e., reduced apex predator abundance) and their combination drive coordinated responses of freshwater ecosystems by evaluating the dynamics of synchrony between control and disturbed mesocosms using high‐frequency dissolved oxygen saturation measurements, an integrative parameter of the metabolic balance of ecosystems. Nutrient enrichment desynchronized the oxygen dynamics and their component cycles between treatments, likely arising from elevated primary production. Warming and overexploitation tended to desynchronize oxygen cycles from the control, particularly at short time scales. Nutrient enrichment combined with warming dampened desynchronization between control (ambient) and treatment mesocosms, whereas desynchronization was enhanced when simultaneously subject to predator overexploitation. As one of the first experimental demonstrations of global change impacts on ecosystem synchrony, this study highlights the need—and opens new avenues—to detect alterations in ecosystem functioning across previously unexplored spatial and temporal scales
Enhanced permafrost warming in European mountains in the early 21st century
No full textInternational audienceMountain permafrost, constituting 30% of the global permafrost area, is highly sensitive to climate change and strongly influences mountain ecosystems and communities. This study quantifies 21 st century mountain permafrost warming by compiling a quality-controlled permafrost temperature data set obtained in sixty boreholes at monitoring sites in European mountains. Each time series spans one to three decades, enabling a comprehensive assessment of mountain permafrost warming patterns in Europe, from the Alps, across Scandinavia to Svalbard in the high Arctic. We find consistent permafrost warming patterns across, all observed sites, depths and time periods. For the early 21st century, warming rates at 10 and 20 meters depth exceeded 1 °C per decade in cases, and are generally higher than previously reported as a result of both, accelerated warming and a more comprehensive data set. Substantial warming notably occurs at cold and ice-poor bedrock sites at both high latitudes and high elevations, with the permafrost warming rates being comparable to warming rates of air temperature.For ice-rich sites close to the melting point instead, latent heat effects reduce temperature changes, thus obscuring important changes ongoing in ice-rich permafrost substrates.</p
Hydrogeochemical processes, reaction rates and effect of spatial scales in carbonate critical zone observatories: insights from the reactive-transport modeling of C-Q relations in four mountain watersheds
No full textInternational audienceThis study investigates hydrogeochemical processes, reaction rates and the effect of spatial scales in mountain carbonate watersheds. A reactive-transport model was deployed to capture the concentration-discharge relations (C-Q relations) of major solute species measured in the river waters of two critical zone observatories located in the south of France (southern Alps and Ardèche). The specific control of evaporite, carbonate and clay minerals on river water geochemistry is identified by the reactive-transport modeling. The dissolution of carbonate and evaporitic minerals strongly controls C-Q relations in Na+, Ca2+, Mg2+, SO42- and Cl- solute species. The key role of evaporite dissolution cannot be neglected in the studied Alpine watersheds. The dissolution/precipitation of clay minerals and the surface remobilization is more important for shaping C-Q relations in H4SiO4 and K+. Concerning the coupling between hydrological and geochemical processes, the chemostatic behavior of rivers and the observation of overland flow events during high discharge periods can be reconciled by considering the evolved overland flow observed on hillslopes and characterized by high solute concentrations. Overland flow may lead to an overestimation of water transit time at high flow if elevated solute concentrations from overland flow sources are attributed to time-dependent weathering reactions. The C-Q relations in Ca2+ and Mg2+ are overestimated by our reactive-transport model, and the reactive surface area of calcite and dolomite must be reduced by 4–5 orders of magnitude in the input of the model to capture the measured data. We interpret this discrepancy as a result of probable subsurface heterogeneity in carbonate watersheds, since macroporosities and fractures can strongly decrease the apparent mineral reactive surfaces in the field. For the effect of spatial scales, shifting from elementary (<5 km2) to mesoscale watersheds (20–50 km2) has little impact on the geochemical composition of river waters while differences in hydrological functioning are observed. This absence of geochemical contrast cannot be only explained by equilibrium concentrations, but must also imply a geomorphological control on water transit times. Finally, our work highlights the importance of multi-observatory investigations. It also demonstrates that a thorough knowledge of the regional geology is key to understand the critical zone architecture, its mineralogical composition and the main hydrogeochemical processes
Effect of pH and temperature on olivine dissolution anisotropy
No full textInternational audienceOlivine is a ubiquitous mineral in mafic and ultramafic environments, whose reactivity has recently received a renewed interest for the study of extraterrestrial environments and the development of carbon capture and storage technologies. While olivine dissolution has long been qualitatively described as occurring preferentially following specific crystallographic orientations, determination of kinetic parameters capturing the anisotropy of olivine dissolution and the underlying mechanistic controls is still lacking. In the present study, the dissolution rate of four major faces (r (hkl) ) of olivine was monitored as a function of pH and temperature using nanoscale measurements of surface microtopography before and after dissolution. At temperatures ranging between 30 • C and 90 • C, the reactivity of olivine faces was found to observe the following trend: r (010) > r (130) > r (111) > r (110) . At 90 • C and pH range between 1 and 6, the reaction order with respect to a H + was found to be face-specific and vary between n = 0.65 for the (010) face and n = 1.07 for the (110) face. Furthermore, n for (010) was the same within uncertainty at 30 • C (n = 0.66). The results are also consistent with an activation energy that neither depends on surface orientation, nor on pH for the (010) face, and which is on the order of 60-70 kJ⋅mol -1 . Finally, the relative reactivity of the investigated faces was found to be dictated by their surface energy determined by ab initio calculations, as predicted by the stepwave model. Overall, this study paves the way to the development of physically more robust models of crystal reactivity, of prime importance to predict the reactivity of olivine in a broad range of contexts