HAL-BRGM, les publications scientifiques en libre accès du BRGM
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Géostatistique et cartographie du fond pédo-géochimique: Test d'application du filtrage géostatistique sur le jeu de données METOTRASS
No full textInternational audienceThe national method for managing polluted sites and soils, as well as the management guides for excavated soils, refer to pedo-geochemical backgrounds as reference values for soil quality. However, due to the absence of specific sampling for determining these values at local or regional scale, a method of geostatistical mapping by filtering by krigeant analysis, aimeing at separating anomalies from the background, was developed (Sauvaget et al, 2022). First tested at the scale of an urban center district, it is here tested at the scale of a department via the METOTRASS dataset. The results obtained show that the method is applicable directly for zinc (taking into account the relationship with altitude) or more indirectly for arsenic, lead and copper by partitioning the territory. Finally, ungrouping applied to data appears to be essential in the statistical processing of data with heterogeneous spatial distribution, as is often the case for data in urban areas.La méthode nationale de gestion des sites et sols pollués, de même que les guides de gestion des terres excavées se réfèrent aux fonds pédo-géochimiques comme valeurs de référence pour la qualité des sols. Or, du fait de l'absence d'échantillonnage spécifique pour la détermination de ces valeurs à échelle local ou régionale, une méthode de cartographie géostatistique par filtrage par analyse krigeante, visant à séparer les anomalies du fond, a été développée (Sauvaget et al, 2022). D'abord testée à l'échelle d'un quartier de centre urbain, elle est ici expérimentée à l'échelle d'un département via le jeu de données METOTRASS. Les résultats obtenus montrent que la méthode est applicable directement pour le zinc (en tenant compte de la relation avec l'altitude) ou plus indirectement pour l'arsenic, le plomb et le cuivre en partitionnant le territoire. Enfin le dégroupement appliqué aux données apparait comme primordial dans le traitement statistique de données à la répartition spatiale hétérogène comme c'est souvent le cas pour les données en milieu urbain
Implicit EXP-RBF techniques for modeling unsaturated flow through soils with water uptake by plant roots
No full textInternational audienceRoot water uptake Soil-water-plant interactions Meshfree methods Localized radial basis function EXP-RBF BDF2Modeling unsaturated flow through soils with water uptake by plant root has many applications in agriculture and water resources management. In this study, our aim is to develop efficient numerical techniques for solving the Richards equation with a sink term due to plant root water uptake. The Feddes model is used for water absorption by plant roots, and the van-Genuchten model is employed for capillary pressure. We introduce a numerical approach that combines the localized exponential radial basis function (EXP-RBF) method for space and the second-order backward differentiation formula (BDF2) for temporal discretization. The localized RBF methods eliminate the need for mesh generation and avoid ill-conditioning problems. This approach yields a sparse matrix for the global system, optimizing memory usage and computational time. The proposed implicit EXP-RBF techniques have advantages in terms of accuracy and computational efficiency thanks to the use of BDF2 and the localized RBF method. Modified Picards iteration method for the mixed form of the Richards equation is employed to linearize the system. Various numerical experiments are conducted to validate the proposed numerical model of infiltration with plant root water absorption. The obtained results conclusively demonstrate the effectiveness of the proposed numerical model in accurately predicting soil moisture dynamics under water uptake by plant roots. The proposed numerical techniques can be incorporated in the numerical models where unsaturated flows and water uptake by plant roots are involved such as in hydrology, agriculture, and water management.</div
Publisher Correction to: Sedimentary and metamorphic processes priming black shale for magmatic assimilation of sulfur: an example from the Virginia Formation, Minnesota, United States
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Social insects behind the microgranular structure of Ferralsols: Consequences for their physical fertility when cultivated
No full textInternational audienceIt was long accepted that the microgranular structure which is characteristic of many Ferralsols was mainly related to physico-chemical processes and to their mineralogical composition. It now appears, however, that this microgranular structure originates from the burrowing activity of termites and ants. Given its importance for the physical properties of Ferralsols, it will be necessary to study the different termite and ant species responsible for this microgranular structure and the characteristics of the burrowing activity associated with species. This is a major point to better understand the possible long-term consequences of agriculture on Ferralsol properties because it strongly affects soil faunal biodiversity Most yellow or red soils found in the South American, African and Asian tropics are classified as Ferralsols in the World Reference Base (IUSS Working Group WRB, 2015). They correspond to Latosols in the Brazilian taxonomy (Embrapa, 2006), mainly to Ferrallisols in the Genetic Soil Classification of China and to Ferrosols in the Chinese Soil Taxonomy (Shi et al., 2004 and 2006), and to Oxisols or Ultisols in the Soil Taxonomy (Soil Survey Staff, 2006). They represent a large land surface area with 750 million hectares worldwide (IUSS Working Group WRB, 2015), which corresponds in the tropics to about 14 % of the land surface area. They result from a long sequence of deep weathering under conditions that in most cases have prevailed for at least several tens of thousands of years (van Wambeke, 1992; Scholten et al., 1997; Schaefer, 2001). In such soils, easily weatherable primary minerals such as feldspar and micas have disappeared, resulting in a fine material essentially made up of kaolinite and of iron and aluminium sesquioxides (Pédro, 1968; Melfi and Pédro, 1977, 1978). As a result, Ferralsols are characterized by extremely low native chemical fertility, resulting from very low nutrient reserves, low pH, high phosphorus retention by oxide minerals, and low cation exchange capacity (Yu, 1997; Kögel-Knabner and Amelung, 2014). On the other hand, most Ferralsols are characterized by a well-developed microgranular structure and consequently exhibit high physical fertility resulting from high porosity, low resistance to root penetration, high infiltration rate and high available water retention (Stoop
A path towards precision border irrigation combining hydrodynamic modelling and in-field sensor-based support
No full textInternational audienceSurface irrigation is often described as low performing insofar as its practice is labour intensive and involves the use of large water flows that are difficult to quantify and manage. However, this method remains predominant worldwide, and modernisation towards localised irrigation systems is not always feasible nor advisable. To support border irrigation management, we previously developed a low-cost sensor for surface irrigation management, which remotely informs the farmer of water arrival downstream of his field and therefore of the moment to stop irrigation. The objectives of this article were: (i) to determine the optimal position of this sensor lengthwise in the field throughout the season, and (ii) to compare the influence of management scenarios (current farmer’s practices, sensor-based and time-based cutoff) on irrigation performance. To this end, an integrated agro-hydraulic model was developed to simulate surface water flow dynamics throughout the season including variations in infiltration and roughness. The model was run using monitoring data from the border irrigation of a hay field during a whole season in Southern France. The results showed that the optimal sensor position can change significantly over the course of the season, depending on inflow rates, initial soil moisture and Manning’s roughness. Sensor-based irrigation control was found to be more efficient than current farming practices, with an estimated water-saving potential of 33%, and more effective than an optimised fixed cutoff time in limiting water losses induced by variability or uncertainty in the initial conditions. For some irrigation events, water savings could reach 50%. The methods and findings should serve as a basis for larger-scale studies integrating the adoption of sensors and real-time data for surface irrigation management
L'urbanisation et l'intensité de gestion des sols urbains modifient le cycle de l'azote et les fonctions microbiennes
No full textInternational audienceL’urbanisation modifie en profondeur les cycles biogéochimiques du sol, notamment celui de l’azote (N), à travers l’usage des sols, l’intensité de leur gestion et les apports exogènes. Ces transformations affectent les communautés microbiennes et le fonctionnement du sol, ce qui peut réduire la fertilité, entraîner des pertes de nutriments et accroître les risques environnementaux (pollution des eaux, émissions de gaz à effet de serre). Cette étude explore comment différents types d’usages des sols urbains – jardins vitrine, parcs, zones arborées, bords de routes, zones résidentielles, terrains de sport et réserves foncières – influencent les processus du cycle de l’azote et la structure fonctionnelle des communautés microbiennes. L’étude a combiné des approches biogéochimiques (concentrations de NH₄ ⁺, NO₃ ⁻, azote total), fonctionnelles (taux de minéralisation, nitrification et dénitrification potentielle) et moléculaires (abondance des gènes fonctionnels liés au cycle de l’azote, tels que amoA, nirK, nirS, nosZI, nosZII) couplées à des analyses de diversité (séquençage Illumina MiSeq) pour caractériser les fonctions microbiennes impliquées dans la transformation de l’azote. Les résultats montrent une forte variabilité de la dynamique du cycle de l’azote selon l’usage du sol. Les jardins vitrine urbains présentent des concentrations en nitrate significativement plus élevées, attribuées à une fertilisation minérale intense, à une nitrification accrue et à une abondance plus élevée de gènes amoA. À l’inverse, le potentiel de dénitrification est plus marqué dans les parcs, zones résidentielles et bords de route, où les sols sont plus humides et moins aérés ; conditions favorables aux bactéries dénitrifiantes. La modélisation par équations structurelles (SEM) a permis d’identifier les facteurs clés du fonctionnement du cycle de l’azote en milieu urbain. Le carbone organique du sol (SOC) apparaît comme un déterminant central de la dénitrification, tandis que le pH est fortement corrélé à l’abondance des archées oxydatrices de l’ammonium (AOA). Sur le plan de la composition des communautés bactériennes, l’étude révèle que les fonctions liées au cycle de l’azote varient selon l’usage du sol. Les zones très peu gérées (réserves foncières) abritent davantage de bactéries fixatrices d’azote, tandis que les zones fortement gérées (jardins vitrine, terrains de sport) montrent une prédominance de bactéries impliquées dans la nitrification. Par ailleurs, l’absence de corrélation significative entre les différentes étapes du cycle (minéralisation, nitrification, dénitrification) dans les zones gérées intensivement indique une rupture du cycle de l’azote, probablement liée à l’aération excessive, au travail du sol et à la faible accumulation de matière organique. Enfin, des différences notables de composition des communautés végétales et de gestion influencent également la dynamique de l’azote. Ces résultats soulignent la sensibilité du cycle de l’azote à l’usage des sols en milieu urbain et offre des leviers pour une gestion plus durable de ces milieux : limitation de la fertilisation minérale, conservation de la matière organique, réduction du compactage et mise en place d’une végétation plus diversifiée. Elle plaide pour une meilleure intégration des processus biogéochimiques dans la planification urbaine, afin de renforcer la résilience des écosystèmes urbains face aux pressions anthropiques et climatique
Role of organic matter on the bioenergetic landscape of mine tailings
No full textInternational audienceEurope hosts more than 6 Gt of mining waste, most of which containing iron (Fe), sulfur (S), and toxic pollutants including arsenic (As) or metals. Assisted phystostabilization prevents contaminants transfer by erosion. However, the organic matter brought by amendments represents an additional source of electrons, which modifies the nature and the magnitude of the microbially-mediated redox reaction shaping the energetic landscape, hence on As and metal mobility. To assess the response of microbial activities to change in energy availability and its effects on As mobility, long-term (3 months) batch experiments were conducted under anaerobic conditions, involving fine tailings from an old tin mine (water-rock ratio of 10). Different energy conditions were fixed by adding acetate to reach initial concentrations of 0, 1.19 ,12.0, 24.2 µM. Water was sampled weekly for assessing the main physical and chemical properties. Microbial functional diversity (most probable number) and more refine monitoring of porewater chemistry were done every month. A thermodynamic geochemical model, using WORM portal with its database (modified), was used to interpret the experimental results. During the first month, NO3- concentrations decreased and FeII concentrations increased, as a consequence of the reductive dissolution of iron hydroxide catalyzed by a FeIII-reducing microbial community. The increase of pH from 6.5 to 7.3 results in the desorption of AsV from the iron hydroxides and an increase of AsV concentrations from 0.23 to 5.63 µM after 3 months. In parallel, the concentration of AsIII increases, consistent with the presence of AsV-reducing microorganisms. Yet, considering either the measured Eh or the calculated EhFeIII/FeII at equilibrium with ferrihydrite, the AsV reduction is not energetically favorable. Bioenergetic calculation highlights the role of organic matter as an electron donor in the AsV reduction. Moreover, electron balance calculation indicates that the number of electrons provided by the oxidation of acetate was not enough to fuel all the reduction reactions observed, suggesting that the traces of natural organic matter initially present in the tailing (bark, dead roots, TOC<0.02wt.%) have been used by microorganisms. Bio-molecular analyses are currently performed to determine the microbial functional diversity and further constrain the bioenergetic calculations
L'État, l'eau et la terre. 70 ans de politiques agricoles au Maghreb *
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Volcanism in the Comoros Archipelago, Madagascar, and the East African Rift: What is the link?
No full textInternational audienceThe Comoros archipelago located in the western Indian Ocean has been a topic of debate for ca. 50 years regarding its origin. Various mechanisms have been proposed to explain its formation, ranging from the impact of a mantle plume to the development of a plate boundary between the Somalia and Lwandle plates. Determining the timing of the volcanic activity is crucial to understanding the archipelago's origin. Despite recent geochronological studies, the age of the initial volcanic eruptions on the islands remains uncertain due to the difficulty of accessing the earliest lavas. This study uses high-quality seismic reflection profiles and regional stratigraphy to identify the first volcanic series that marked the onset of volcanism on each island of the Comoros Archipelago. Our findings reveal that localized volcanic activity began ca. 32 Ma at Zélée and Geyser banks and Mayotte edifice, the eastern portions of the archipelago, much earlier than previously believed. Volcanism spread across the Comoros archipelago ca. 9-8 Ma, from the northern part of the Mayotte edifice to Mohéli Island in the west. Ca. 4 Ma, volcanic activity occurred on Anjouan Island and the Jumelles seamounts, followed by Grande Comore Island ca. 2 Ma. This progression of ages from east to west indicates a chronological sequence over time. The timing of volcanic activity in the Comoros archipelago is similar to the magmatism evolution documented at Madagascar and along the East African Rift System (EARS). Magmatic activity began in the late Oligocene, followed by quiescence during the middle Miocene, and resumed in the late Miocene, coinciding with widespread deformation along the EARS, including its offshore branches and Madagascar. Our study shows that the regional tectonic control of volcanic activity in the Comoros archipelago began during the early Miocene, thereby suggesting that the Comoros archipelago developed as an offshore branch of the EARS south of the Somalian plate at that time
A novel clay shrink-swell buildings damage model: From unstructured insurance data to the creation of buildings database, and the proposition of damage severity scale
No full textInternational audienceExpansive clay soils undergo seasonal moisture fluctuations, swelling when wet and shrinking during dry periods. These volumetric changes induce differential ground movements beneath buildings, often resulting in structural damage, particularly in low-rise residential buildings. In France, this phenomenon has become increasingly costly, with average annual insurance claims of 1 billion euros between 2016 and 2021, rising to 3.5 billion euros in 2022 due to severe droughts and heatwaves driven by climate change.Despite its growing impact, damage assessment remains challenging due to the scarcity of empirical data and the localized variability of soil-structure interactions. To address this, we propose a scalable, data-driven methodology that combines expert knowledge and advanced natural language processing to enable empirical risk analysis.This study introduces the Clay Shrink-Swell Damage Severity Scale, constructs a structured database of building and environmental characteristics, and identifies damageability factors based on observed damage levels. A total of 10,325 loss adjustment reports from Generali (2000–2021) were analysed. A subset of 155 reports was manually annotated and scaled to the full dataset using Large Language Models (LLMs) under a Retrieval-Augmented Generation (RAG) framework.The resulting tools provide a solid foundation for post-event assessments, support rapid field diagnostics, and enable the development of personalized prevention strategies. This work contributes to improved vulnerability modelling and more effective risk reduction in a changing climat