HAL-BRGM, les publications scientifiques en libre accès du BRGM
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Contrasting impacts of irrigation and deforestation on Lancang-Mekong River Basin hydrology
No full textInternational audienceIrrigation expansion and subsequent deforestation substantially affect large basin variability. However, given the complex interactions between hydrological variables, a more comprehensive understanding of the hydrological impacts within the coexisting land use changes is needed. Here, we applied surface-groundwater-coupled simulations with historical river gauges and satellite observations to evaluate long-term and seasonal changes in Lancang-Mekong River Basin hydrology. Increasing irrigation elevated soil moisture but depleted groundwater storage. Conversely, deforestation reduced soil moisture, and increased lateral flow in areas with steep terrain compensated for groundwater depletion. Irrigation affected runoff by augmenting evapotranspiration and baseflow, which had opposite implications for runoff changes, causing a mixed spatial pattern of decreases and increases. Meanwhile, decreases in soil moisture due to deforestation offset increases in evapotranspiration due to irrigation, resulting in wider areas of runoff increases than decreases. These illustrate the distinct hydrological impacts of different land use changes and a pathway to complex system assessment
Using cathodoluminescence as a traceability tool for lithium ores and concentrates
No full textInternational audienceNowadays, the ubiquitous use of electronic devices and the generalization of electric powered vehicles results in an unprecedented need for batteries. Lithium, one of batteries main components, is found in brine and rock deposits. Rock deposits represent ca. 60% of the world production. The first step of the extraction of Li from these rocks is the extraction of the Li-bearer minerals through crushing, sieving, and magnetic, density and flotation separation steps to obtain a mineral concentrate. Most common Li-bearer minerals are spodumene and lepidolite.This study is part of the EU-funded MaDiTraCe (Material and Digital Traceability for the Certification of critical raw materials) project working at setting up traceability methods for critical raw materials used in the manufacture of electric vehicle batteries (lithium, cobalt, REEs and graphite). This comes as a response to the growing demand from manufacturers and consumers to promote materials from environmentally and ethically responsible sources, and to the rapid evolution of regulatory frameworks aiming to ensure the respect of local legislations and to protect states sovereignty. One of the objectives of the MaDiTraCe project is the development of cost efficient and easy to implement analytical protocols to be applied at key steps of the value chain and that can be used routinely to monitor the origin of materials and transformed products. Optical cathodoluminescence is a relatively cheap analytical method that has shown its potential for source tracing (e.g. [1], [2]). Mineral concentrate pellets from various origins are exposed to the cathodoluminescence electron beam and data are recovered under the form of RGB images. The complete imaging of a pellet takes at most 15 minutes. Images are treated to extract each sample luminescence characteristics such as colors, intensities, and proportions of color/intensity groups. Data obtained define sample specific signatures that can be used to differentiate concentrates of different origins. Results rely mainly on the general luminescence of the sample (controlled by the main Li-bearer) and on the luminescence of accessory minerals present as traces
DEVELOPPEMENT DE LA DENDROCHIMIE APPLIQUEE AUX SITES POLLUES: Approche multi techniques pour l’analyse des traceurs et co-traceurs des polluants cerne par cerne
No full textInternational audienceLes sols contaminés par des polluants organiques et métalliques dus aux activités minières et industrielles nécessitent une gestion efficace pour des raisons environnementales, sanitaires et économiques. La dendrochimie, qui utilise les arbres comme bioindicateurs pour enregistrer la pollution, est une méthode prometteuse pour diagnostiquer ces sols. Le projet GESIPOL ARGOS, coordonné par le BRGM et en partenariat avec TAUW, Chrono-Environnement et l'INRAE, vise à développer une méthode dendrochimique pour mesurer les traceurs de ces pollutions dans les arbres cerne par cerne. Cette méthode peu coûteuse et rapide est adaptée aux zones difficiles d'accès, et permet de comprendre la diffusion d'une pollution à l'échelle d'un site. Durant la première année du projet, des carottes d'arbres prélevées sur le site de Vieux-Charmont ont été analysées, révélant les avantages et limites des techniques utilisées (microdensitométrie, µEDXRF et LA-ICP-MS). Le programme ARGOS a été développé sur Spyder utilisant le langage python pour traiter les données issues des analyses élémentaires. Les prochaines étapes du projet incluent l'amélioration et le développement des différentes techniques d'analyses bénéfiques au projet, ainsi que le programme ARGOS. Enfin la méthode développée sera testée sur des sites contaminés par des métaux et des composés organiques
Leaching of pollutant metals (Pb, Zn) from abandoned mine tailings: A multicomponent reactive transport model of a pilot-scale experiment
No full textInternational audienceMine tailing deposits pose a global problem, as they may contain metal contaminants in various geochemical forms and are likely to be leached from the surface into the underlying groundwater, which can result in health and/or environmental risks. Unfortunately, little is currently known regarding the water flow and mass balance related to leaching in the vadose zone as these factors are still difficult to measure at the field scale. A pilot-scale experiment was run in a 1 m3 instrumented column for 6 months to address this issue. This 70 cm high column was filled with highly Pb-contaminated tailings and then watered regularly. The top half remained unsaturated while the bottom half was kept saturated. Continuous water flow and water saturation measurements were recorded and the physico-chemical properties of the soil solutions were monitored weekly at different levels in the column. A 1D multicomponent reactive transport model was built to simulate the fate and transport of Pb as well as other elements. The variably saturated water flow was simulated using the Richards equation, while the van Genuchten analytic form was used to describe the unsaturated soil hydraulic properties. The main processes considered to simulate the reactive transport were advection-dispersion, thermodynamic equilibrium, and kinetically-controlled dissolution-precipitation reactions. The most reactive Pb-bearing phases accounted for in the simulation were anglesite (PbSO4) and plumbojarosite Pb0.5Fe3(SO4)2(OH)6. The simulations accurately reproduced the water flow and mass balance as well as the drop of 2 pH units experimentally measured in the pore solution. This trend resulted from plumbojarosite dissolution followed by ferrihydrite precipitation. The increased Pb concentration in the soil solution induced by the dissolution of Pb-bearing phases was partially offset by Pb-sorption onto newly formed iron oxides and the precipitation of secondary mineral phases, e.g. anglesite. The modeling results could be used to assess potential risks of groundwater contamination by mine tailings
Phases of Magmatism and Tectonics Along the Madagascar‐Comoros Volcanic Chain, and Synchronous Changes in the Kinematics of the Lwandle and Somalia Plates
No full textInternational audienceThis paper aims to solve the longstanding debate on the origin of the Comoros volcanic archipelago (Mozambique Channel, Indian Ocean) concerning whether it represents a hotspot trail or a boundary between the Lwandle and Somalia plates in possible connection with the East African Rift System (EARS). To achieve this goal, we analyzed rock samples from recently discovered and previously uninvestigated volcanoes and edifices by means of geochemistry and geochronology. Major-trace element analyses and radiometric dating ( 40 Ar/ 39 Ar, K-Ar, and (U-Th)/He) allow us to identify a widespread phase of Comorian volcanism initiated at 9-8 Ma, involving the Zélée, Geyser, and Leven banks, three atolls east of the Comoros. Another tectono-magmatic phase initiated at 2.5 Ma led to a N-S widening of seamount volcanism, and to the progressive development of en-échelon NW-SE structures. With this new addition of atolls and seamounts, the Comoros Archipelago becomes a ∼700 km-long, ∼200 km-wide E-W chain extending from the Cenozoic volcanoes of Madagascar to the EARS. The reactivation of this chain at 9-8 and 2.5 Ma coincides with abrupt changes in the motion of the Somalia plate relative to the Lwandle plate, and with plate boundary modifications. The en-échelon reorganization of structures also matches the kinematic evolution of Somalia relative to Lwandle, from transtension (>3 Ma) to pure dextral slip (≤3 Ma) in the northern Mozambique Channel. We conclude that the Madagascar-Comoros volcanic chain is a branch of the EARS and a plate boundary, further strengthening the link between magmatism and the Rovuma-Lwandle-Somalia plate kinematic
De dunes fixes à transgressives, conditions et temporalités de la transition le long de la côte Aquitaine, France
No full textInternational audienceToday most of the coastal dunes in temperate latitudes, especially in the northern hemisphere, are relatively stable. However, over the last decade, the Gironde coast has experienced substantial dune remobilization following a major marine erosion event. The qualities of the dataset used (continuity in time and space) based on annual airborne LiDAR and Satellite imagery (Sen-tinel-2) allow a detailed description of the morphological change and establish relations with forcing and controlling factors (vegetation cover, geomorphological descriptors). Between 2014 and 2023, about 10 km of the Gi-ronde dunes have switched from fixed dunes to transgressive dunes. The analysis showed that in the vast majority of the cases the dominant process involved was dune front cannibalism. However, there is considerable spatial and temporal variability in the transition to a transgressive dune along the coast, depending on the amount of sediment remobilized and the morphological parameters of the dunes (steepness of the front slope, width)
Devenir de substances émergentes depuis une ancienne décharge: Transfert de substances émergentes par les eaux souterraines depuis une ancienne décharge municipale (Nantes, France)
No full textInternational audienceSites contaminated by point source pollution such as landfills frequently impact the quality of groundwater. Due to the diversity of waste deposited, landfills are sources of a wide variety of contaminants, including emerging substances. The former municipal landfill of Prairie de Mauves, located in Nantes (France) on alluvium of the Loire estuary, illustrates this. This pilot site is part of the SAFIR network and of the national observation system on cities (SNO Observil). Daily recording of piezometric levels, groundwater electrical conductivity and temperature at different points has been in place since 2014. 9 emerging substances were searched for among more than 80 quality parameters between 2013 and 2019 in leachate as well as in the groundwater upstream and hydraulically downstream of the site. Six (6) emerging substances were quantified in the leachates, including endocrine disruptors (such as Bisphenol A up to 23 µg/l and tolyltriazole up to 0.87 µg/l). Most of the substances detected in the leachate were found in groundwater immediately downstream of the site, much less a few hundred meters further. Bisphenol A is found far downstream.Former landfills are likely to generate diffuse pollution of continental (ground and surface), estuarine and marine waters. Impacts on (aquatic) fauna are also possible. A better characterization of the molecules generated by these sites therefore appears necessary, as does a better understanding of their fate.Les sites contaminés par des pollutions ponctuelles comme les décharges impactent fréquemment la qualité des eaux souterraines. Du fait de la diversité des déchets déposés, les décharges sont sources d'une grande variété de contaminants, incluant des substances émergentes. L'ancienne décharge municipale de la Prairie de Mauves, située à Nantes (France) sur des alluvions de l'estuaire de la Loire, permet de l'illustrer. Ce site atelier fait partie du réseau SAFIR et du SNO Observil. Un enregistrement quotidien des niveaux piézométriques, de la conductivité électrique et de la température de l'eau souterraine en différents points est en place depuis 2014. 9 substances émergentes ont été recherchées parmi plus de 80 paramètres de qualité entre 2013 et 2019 dans les lixiviats ainsi que dans les eaux souterraines en amont et en aval hydraulique du site. Six (6) substances émergentes ont été quantifiées dans les lixiviats, incluant des perturbateurs endocriniens (comme du Bisphenol A jusqu'à 23 µg/l et du tolyltriazole jusqu'à 0.87 µg/l). La plupart des substances détectées dans les lixiviats ont été trouvées dans les eaux souterraines en aval immédiat du site, beaucoup moins quelques centaines de mètres plus loin. Le Bisphenol A est trouvé en aval éloigné. Les anciennes décharges sont susceptibles de générer des pollutions diffuses des eaux continentales (souterraines et superficielles), estuariennes et marines. Des impacts sur la faune (aquatique) sont également possibles. Une meilleure caractérisation des molécules générées par ces sites apparait ainsi nécessaire, de même qu'une meilleure compréhension de leur devenir
Importance of hydraulic process in induced seismicity modeling
No full textInternational audienceInduced seismicity is often modeled as the reactivation process of a fault due to pore pressure change. The known inputs are mostly the injected fluid flux and well-head pressure. The output is the spatio-temporal distribution of the seismicity, detected by the seismograms. The medium should be hydraulically and mechanically heterogeneous and complex and its characteristics are often calibrated with the on-going process. From the point of view of earthquake generation process, we often take into account the non-linearity or randomness of the faulting in friction, while the diffusion process of the fluid is often over simplified. In the infinite, isotropic and homogeneous porous medium, the pore pressure change can be analytically written, noting that there remains a singular point at the injection point. On the other hand, it is also possible to consider that the porosity (e.g
Delayed environmental pollution caused by transient landscape storage — An example from the Lesser Antilles
No full textInternational audienceThe strong pest pressure on intensive banana cultivation in the French West Indies led to the intensive use of chlordecone (an organochlorine insecticide) between 1972 and 1993. Due to its high toxicity for the population and the environment, many studies were conducted on the transfer of chlordecone over the last 20 years. However, most studies focused on the dissolved fraction of chlordecone, while the particle-bound fraction was understudied. Therefore, this study reconstructs pluri-decadal erosion rates ( 1980–2023) and associated chlordecone particle-bound transfers from soil and sediment cores sampled in a cultivated headwater catchment (Saint-Esprit, Martinique). Based on sediment accumulation analyses in an agricultural reservoir, high erosion rates ( 10 t ha−1 yr−1) were found in the investigated catchment during the study period, with values exceeding the estimated tolerable soil loss rate in tropical contexts ( 2.2 t ha−1 yr−1). Based on the analysis of soil cores sampled along a banana plantation hillslope, this study highlights the formation of colluvial deposits with high levels of chlordecone contamination. When these areas are affected by erosion processes, this leads to massive remobilization of particle-bound chlordecone to water bodies. Indeed, in sediment sampled in the downstream reservoir, we observed a drastic increase in these transfers since 2006, synchronous with changes in agricultural practices. This study therefore highlighted the occurrence of legacy contamination at toeslope positions, which was estimated to potentially persist for 4000 to 11,000 years. Such a residence time highlights the need to implement changes in land management to effectively reduce erosion of agricultural soils, particularly in areas identified as ”temporary deposition zones” for chlordecone contamination, in order to protect downstream water bodies from chlordecone transfer. To achieve this, agricultural practices that may increase soil erosion, such as herbicide application or intensive ploughing, should be minimized. Overall, this study improved our understanding of erosion and associated chlordecone transfers in tropical environments
Manure contribution to rural livelihoods at farm and landscape levels: a systemic approach in semi-arid Central Tunisia
No full textInternational audienceManure valorization through on-farm use or market transactions is an ancient and widespread practice in the mixed crop-livestock systems of the semi-arid areas of North Africa. While research has long focused on the manure contribution to soil fertility at the plot level, little has been done concerning livelihood conditions. The present paper aims to assess the contribution of manure use and exchange on the livelihoods of rural communities using an original dataset collected in 2021 among 150 farmers in Central Tunisia. This analysis is carried out within the analytical agroecology framework combined with factor analysis methods. Results showed that manure use and valorization differ along the watershed, from a socioeconomic perspective in small farms operating under rainfed tree-pastoral systems, to an environmental and agronomic perspective in the mixed rainfed-irrigated systems downstream. Manure flow analysis confirmed that on-farm manure balance is positively correlated to economic wealth. However, the manure fluxes questioned the environmental sustainability of the vulnerable zones. Its use and management could significantly impact livelihood discrepancies in the future, with the increasing of demand and use of manure in more favorable zones such as irrigated lands at the detriment of the rainfed zones