HAL-BRGM, les publications scientifiques en libre accès du BRGM
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One hydrothermal system may hide another: Insights from a geochemical exploration of Chaudes-Aigues and nearby springs (French Massif Central)
No full textInternational audienceGranitic-hosted hydrothermal systems offer valuable insight into deep fluid circulation mechanisms in amagmatic contexts. This study focuses on the Chaudes-Aigues hydrothermal system in the French Massif Central, which hosts one of the hottest natural springs in Europe (Par Spring, 80-82 • C). Our work aims to better constrain the functioning of the system, including reservoir temperature, recharge zone, and fluid pathways. A combined approach of water geochemistry (major elements, isotopes) and thermo-hydraulic numerical modelling was applied. Using 22 thermal springs distributed across the Margeride Granitic Complex (MGC) and the Cantal Volcanic Complex (CVC) the temperature of Chaudes-Aigues reservoir has been estimated and is thought to reach 190 ± 10 • C, validating and refining previous estimates. Isotopic and geochemical tracers point to a meteoric origin, with the recharge area most likely located along the southern edge of the MGC, connected to the emergence zone via a thick N150E fault zone. This study redefines the Chaudes-Aigues system as fully amagmatic and structurally controlled. Other geothermal reservoirs have also been identified within the Margeride Granitic Complex, with temperatures exceeding 100 • C, indicating a broader geothermal potential of the area. Furthermore, this study highlights the potential for identifying similar hidden geothermal systems in other fractured granites with limited surface manifestations, offering new perspectives for high-temperature geothermal exploration in Europe
Microbial Sulfate Reduction Fed with Phytostabilization Biomass Compost: An Integrated Bioremediation Strategy for Mine Tailings and Drainage
No full textInternational audienceThis study aimed to acquire proof of concept validity, at the laboratory and theoretical levels, of an integrated remediation strategy involving sulfate-reducing bacteria (SRB) and composted phytostabilization plant biomass. A model mine site presenting both historic mine waste dumps and acid mine drainage (AMD) was chosen to test the integrated bioremediation scheme. A microbial consortium from a SRB bioreactor treating AMD was adapted to grass compost as the sole carbon and energy source. It was then used to assess the feasibility of feeding SRB with the AMD of a former tin mine and compost prepared with phytostabilization plant biomass from the site, inducing SO4 reduction and the precipitation of metals (Fe, Co, Ni). A 7-week-old grass compost used at 1–5% (wet weight) efficiently supported SBR activity. Results showed a decrease of sulfate concentration whose maximum amplitude was reached (from 1500 to less than 100 mg/L SO4) with 10% compost (wt% in liquid medium). Sulfate reduction rate increased with compost concentration from 1 to 5%, and the highest efficiency, in terms of mg reduced SO4 by mg of provided compost was obtained with 1% compost. All inoculated cultures induced precipitation of Fe, Co, and Ni. The proportion of SRB genera in the final bacterial communities ranged from 13 to 20%. The proportion of Desulfoscipio and Desulfallas in the SRB community increased with increasing compost concentration. The results suggest that compost from phytostabilization plant biomass is suitable to feed SRB bioreactors for AMD treatment on-sit
Sb(III) and Sb(V) retention by aptian sands: Quantitative insights into adsorption and heterogeneous redox reactions controlled by iron-containing minerals
No full textInternational audienceThe retention of Sb(III) and Sb(V) by Aptian sands, which contain quartz and glauconite, was investigated as a function of Sb concentration and with 7 d and 30 d contact time. Two samples, collected along a vertical profile, were used for the experiments. They originated from the capillary fringe (S CFr ) and saturated (S Sat ) horizons and were respectively representative of oxidizing and reductive redox conditions. The Aptian sands had a lower retention capacity for Sb(V) than for Sb(III). Sb(V) distribution coefficients (R d ) ranged between 10 ± 3 L•kg -1 and 13 ± 4 L•kg -1 in S Sat and between 11 ± 3 L•kg -1 and 19 ± 4 L•kg -1 in S CFr , after 7 d interaction. These values almost doubled when the interaction time was increased to 30 d and, in all conditions, Sb(V) was the only species detected in the aqueous solution. The evolution of Sb(III) R d as a function of Sb equilibrium concentration and time was more complex. When contact time was 7 d, R d first increased from 68 ± 7 L•kg -1 ([Sb] eq = 2.2•10 -8 M) to 547 ± 33 L•kg -1 ([Sb] eq = 1.4•10 -7 M) and then decreased down to 323 ± 21 L•kg -1 ([Sb] eq = 1.1•10 -6 M) for S Sat after 7 d of interaction. Sb(III) retention by S CFr was slightly lower: R d increased from 15 ± 4 ([Sb] eq = 3.4•10 -8 M) to 174 ± 13 L•kg -1 ([Sb] eq = 7.7•10 -7 M) and then decreased down to 137 ± 10 L•kg -1 ([Sb] eq = 2.3•10 -6 M). While Sb(V) was the only species detected in the aqueous solution at lower concentrations, Sb(III) was increasingly present when added Sb(III) concentration increased, hence pointing out to heterogeneous redox interaction between Sb(III) and the solid phase that could be successfully modeled.Overall, this study demonstrated that Sb(III) and Sb(V) retention depended on the speciation of added Sb, on the redox reactivity of the sand samples, and on contact time. Such results are a step forward to our capacity to model, and hence quantitatively predict, Sb mobility in the natural environment
Hydrological responses to land use changes and precipitation variability in Southern Brazil
No full textInternational audienceThis study investigates the relative impacts of rainfall and LULC changes on streamflow variations over the Meridional plateau in the region comprising the Uruguay River basin in Southern Brazil. We used MapBiomas annual LULC data set and the CAMELS-BR data set by aggregating daily observations from gauging stations (rainfall and streamflow) to annual indices from 1985 to 2018. We employed time series and trend analysis across three identified clusters with 78 gauging stations through an unsupervised machine learning algorithm. New hydrological insights for the regions: We found an extensive and statistically significant agricultural expansion for soybean croplands following a transition from other temporary crops (i.e., maize, wheat, oats, etc.), which was accompanied by statistically significant runoff coefficient decrease (i.e., 34 %), while the results for rainfall and flow were statistically insignificant. Furthermore, we observed a 27 % rise in water demand linked to the expansion of soybean croplands, a phenomenon corroborated by existing research. The growth in the number and capacity of dams further may reinforce these findings across the analyzed periods. The identified remarkable decrease in runoff coefficient may, therefore, be primarily attributed to LULC changes. Our findings might provide insights for improved water resource management for future land use planning to develop more resilient catchments against changing environmental and climatic conditions
Beyond Environmental Impact: Coupling Criticality and LCA in Electric Motor Manufacturing
No full textInternational audienceThe necessity of including resource criticality into evaluations of environmental sustainability is highlighted by the rising demand for essential raw materials in developing technologies, especially in clean energy transitions. We investigate how including Supply Risk Potential (SRP) indicators into LCA by taking into account both the resilience of material supply chains and the environmental effect, using the example of a traction motor for an electric vehicle. The study intends to demonstrate the application of the GeoPolRisk method and hence minimizes the complexity of the model by using system processes by use of geopolrisk library. The European Union (EU), the United States of America (US), and Japan are considered locations for a company evaluating supply risk. The five aggregated production processes—magnet manufacture, electrical steel production, copper components, other mechanical parts, and final assembly—are the emphasis of the gate-to-gate system boundary definition.A life cycle inventory model for a 100kW permanent magnet synchronous electric machine is used in the study. OpenLCA with Ecoinvent v3.10 are used to estimate the environmental impact, while the GeoPolRisk method, which is operationalized through a Python library, is utilized to quantify supply risk based on "resource, in ground" flows. The main sources of supply risk and environmental effects in the production of traction motors were found to be aluminum die casting, electrical steel manufacturing, and magnet manufacturing. Magnesium, aluminum, and rare earth elements were shown to be important components causing supply risk, especially because of import dependence and geopolitical considerations in the US, Japan, and the EU. In contrast to SRP indicators, traditional impact categories like global warming potential and Abiotic Depletion Potential Element (ADPE). Due to supply chain linkages and geopolitical governance, SRP prioritizes Rare Earth Elements (REEs), aluminium, and magnesium, whereas ADPE prioritizes commodities like copper and chromium because of global depletion patterns. With commodities like magnesite and REEs exhibiting strong sensitivity to geopolitical events in China and Russia, comparative results across the US, Japan, and the EU demonstrate that country-specific import mixtures greatly influence supply risk outcomes. The study highlights trade-offs and synergies in material selections that conventional LCA could miss by combining supply risk and environmental effect. During the shift to low-carbon technologies, this integrated approach can help drive more informed policy development, sourcing strategies, and material selection, resulting in more resilient and sustainable product systems
L'irrigation et l'agroécologie peuvent-elles faire bon ménage ? Vers une irrigation multiservice
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Relations de travail des ouvrières agricoles en Tunisie : un environnement intégré socialement mais peu propice à une évolution des rapports de pouvoir
No full textSource Agritrop Cirad (https://agritrop.cirad.fr/616493/)International audienceFemale agricultural workers have become indispensable to the functioning of the agricultural economy in Tunisia. However, public policies designed to improve their working and living conditions have, in practice, limited impact. This study examines the relationships that agricultural work compels women workers to establish with various actors, as well as within their households: how these relationships highlight specific power dynamics, and the ways in which they affect the women's daily lives. The research is based on in-depth interviews with 35 female agricultural workers from the governorate of Beja. Findings reveal that women workers operate in an environment that places them in a position of subordination in their interactions with farmers and transporters. At the household level, their work is accepted, yet rarely results in genuine autonomy in decision-making, particularly with regard to the use of resources or life choices. The working environment of female agricultural workers remains socially connected to their communities of origin: workers often interact outside the workplace, while transporters themselves maintain social ties with these communities. Nonetheless, despite this social embeddedness, the environment remains ill-suited to a reconfiguration of power relations initiated by women themselves towards more equitable relations. To be effective, public policies aiming to improve the conditions of female agricultural workers must therefore design intervention mechanisms that focus on transforming the relationships between the workers on the one hand, and the transporters and farmers on the other.Les ouvrières agricoles sont devenues indispensables au fonctionnement de l'économie agricole en Tunisie. Cependant, les politiques publiques élaborées pour améliorer leurs conditions de travail et de vie n'ont en pratique que peu d'impacts. L'étude porte sur les relations que le travail des ouvrières agricoles les amène à avoir avec différents acteurs tout comme au sein de leur foyer : comment ces relations mettent en évidence certains rapports de pouvoir, et les impacts de ces relations sur le quotidien des ouvrières. Des entretiens ont été menés auprès de 35 ouvrières agricoles du gouvernorat de Béja. Les ouvrières évoluent dans un environnement où elles se trouvent dans une position de subordination dans leurs interactions avec les agriculteurs et les transporteurs. Au niveau familial, leur travail est accepté mais souvent ne se traduit pas pour autant par une autonomisation dans les prises de décision notamment quant à l'usage de leurs ressources ou aux choix de vie. L'environnement de travail des ouvrières agricoles est socialement connecté à leurs communautés d'origine : souvent les ouvrières travaillant ensemble se voient hors du travail et les transporteurs ont eux aussi des liens sociaux avec ces communautés. Cependant, malgré cette connexion, cet environnement est peu propice à une reconfiguration des relations de pouvoir, qui serait initiée par les femmes elles-mêmes, vers des relations plus équitables. Pour être effectives, les politiques publiques visant à améliorer les conditions de travail des ouvrières agricoles devront concevoir des dispositifs d'intervention centrés sur la transformation des relations entre les ouvrières d'une part, et les transporteurs et les agriculteurs d'autre part
Data-Driven Models for Alert Management in Infrastructure Monitoring Within Their Environment
No full textInternational audienceThis study investigates the implementation of alert systems for critical infrastructures within their operational environment. The challenge arises from the extensive scale of these infrastructures, the heterogeneity and complexity of the data sources, and the imperative for real-time responsiveness. To address these challenges, we propose data-driven methodologies that demonstrate the feasibility of such systems. Specifically, we examine two complementary case studies: 1) the detection of sinkholes in railway networks and 2) the development of a metamodel for seismic risk assessment in dam infrastructure. These case studies illustrate the pivotal role of artificial intelligence and predictive analytics in enhancing alert systems and facilitating proactive risk management. The proposed approach contributes to the field of critical infrastructure monitoring by integrating advanced data-driven strategies, thereby reinforcing its scientific relevance and novelt
A Bibliographic Analysis of Multi-Risk Assessment Methodologies for Natural Disaster Prevention
No full textInternational audienceIn light of the increasing frequency and intensity of natural phenomena, whether climatic or telluric, the relevance of multi-risk assessment approaches has become an important issue for understanding and estimating the impacts of disasters on complex socioeconomic systems. Two aspects contribute to the worsening of this situation. First, climate change has heightened the incidence and, in conjunction, the seriousness of geohazards that often occur with each other. Second, the complexity of these impacts on societies is drastically exacerbated by the interconnections between urban areas, industrial sites, power or water networks, and vulnerable ecosystems. In front of the recent research on this problem, and the necessity to figure out the best scientific positioning to address it, we propose, through this review analysis, to revisit existing literature on multi-risk assessment methodologies. By this means, we emphasize the new recent research frameworks able to produce determinant advances. Our selection corpus identifies pertinent scientific publications from various sources, including personal bibliographic databases, but also OpenAlex outputs and Web of Science contents. We evaluated these works from different criteria and key findings, using indicators inspired by the PRISMA bibliometric method. Through this comprehensive analysis of recent advances in multi-risk assessment approaches, we highlight main issues that the scientific community should address in the coming years, we identify the different kinds of geohazards concerned, the way to integrate them in a multi-risk approach, and the characteristics of the presented case studies. The results underscore the urgency of developing robust, adaptable methodologies, effectively able to capture the complexities of multi-risk scenarios. This challenge should be at the basis of the keys and solutions contributing to more resilient socioeconomic system
1D modelling of pegmatite migration
No full textInternational audiencePegmatites and rare metal granites are granitic igneous rocks distinguished by their texture, which is dominated by crystal growth. These rocks are frequently enriched in rare elements (e.g., Li, Cs, Be, Nb, Ta) and represent economically significant deposits, classified among the critical raw materials identified by the European Commission. Our objective is to better constrain the tectonic parameters that govern the emplacement of pegmatites within the continental crust, including their migration rates and durations, with a particular emphasis on the role of temperature in these crustal migration processes. To model those fluid migrations, two-phase flow in Julia, based on porosity waves with compressible fluid is used. The porosity is interpreted as melt [1]. To improve the yet existing codes [2], we implement temperature in our two phase flow formulation from energy conservation. Temperature allow a thermomechanical coupling with rock viscosity. A first equation with a simple exponential coupling is used to understand thermal implication on viscosities. The model represents a continental crust with partial melting occurring within the lowermost 5 km, where temperature is maintained at 750°C due to underplating. A constant geothermal gradient is applied from this depth to the surface. A 10% porosity anomaly is introduced in the partially molten zone, while a baseline porosity of 1% is applied throughout the model to ensure numerical stability. The fluid viscosity is set at 10^4 Pa.s, while at 750°C, the rock viscosity is 10^16 Pa.s. A constant permeability of 10^-11 m² is applied throughout the model. Thermomechanical couplings of varying strength are implemented to assess their impact on migration processes. Accordingly, the rock viscosity at 450°C is varied between 10^16Pa.s and 10^21 Pa.s.Models reveals two distinct mechanisms that halt migration. The first occurs when the thermomechanical coupling is low (soft and hot crust). Allowing rock viscosity to remain low, so melt migration can outpace thermal diffusivity. Enabling the melt to be in an undercooling state. This means that the magma can migrate beyond the point at which the surrounding rock reaches the crystallization temperature of the melt, a necessary condition for pegmatite formation. The second case arises when thermomechanical coupling is strong, causing the surrounding rock's viscosity to become too high for the magma to reach undercooling condition. In this scenario, the magma crystallizes as soon as it reaches the surrounding rock at its crystallization temperature, potentially becoming trapped by a viscous layer (of different or colder nature).The use of a geothermal gradient more representative of a metamorphic core complex, along with an improved thermomechanical coupling, should refine the estimates of migration time and distance. Similarly, the introduction of viscous heterogeneity would help highlight the geological structures that may or may not facilitate the migration of these magmas to shallower levels of the crust. References:[1] L. Räss, T. Duretz & Y.Y. Podladchikov (2020). https://doi.org/10.1093/gji/ggz239[2] A. Plunder & al. (2022). https://doi.org/10.1016/j.lithos.2022.10665