Effects of agricultural land use on fluvial carbon dioxide, methane and nitrous oxide concentrations in a large European river, the Meuse (Belgium)

peer reviewedWe report a data-set of CO2, CH4, and N2O concentrations in the surface waters of the Meuse river network in Belgium, obtained during four surveys covering 50 stations (summer 2013 and late winter 2013, 2014 and 2015), from yearly cycles in four rivers of variable size and catchment land cover, and from 111 groundwater samples. Surface waters of the Meuse river network were over-saturated in CO2, CH4, N2O with respect to atmospheric equilibrium, acting as sources of these greenhouse gases to the atmosphere, although the dissolved gases also showed marked seasonal and spatial variations. Seasonal variations were related to changes in freshwater discharge following the hydrological cycle, with highest concentrations of CO2, CH4, N2O during low water owing to a longer water residence time and lower currents (i.e. lower gas transfer velocities), both contributing to the accumulation of gases in the water column, combined with higher temperatures favourable to microbial processes. Inter-annual differences of discharge also led to differences in CH4 and N2O that were higher in years with prolonged low water periods. Spatial variations were mostly due to differences in land cover over the catchments, with systems dominated by agriculture (croplands and pastures) having higher CO2, CH4, N2O levels than forested systems. This seemed to be related to higher levels of dissolved and particulate organic matter, as well as dissolved inorganic nitrogen in agriculture dominated systems compared to forested ones. Groundwater had very low CH4 concentrations in the shallow and unconfined aquifers (mostly fractured limestones) of the Meuse basin, hence, should not contribute significantly to the high CH4 levels in surface riverine waters. Owing to high dissolved concentrations, groundwater could potentially transfer important quantities of CO2 and N2O to surface waters of the Meuse basin, although this hypothesis remains to be tested

Apport de l’étude de la fracturation et de la karstification dans la modélisation des aquifères karstiques.

International audienceLe comportement des aquifères karstiques à long terme ne peut être estiméqu’au travers de l’utilisation de modèles qui permettent de modéliserla réponse et le stockage d’eau de ces aquifères. Une bonneconnaissance de la structure de ces aquifères fortement hétérogènes estprimordiale afin de mettre en oeuvre des modèles robustes d’exploitationdurable de la ressource. Nous proposons une approche qui associel’analyse de la fracturation à plusieurs échelles (de micro à meso) àcelle du contexte géomorphologique, afin de déterminer les axes préférentielsd’écoulements au sein d’aquifères karstiques. Ces axes préférentielsd’écoulements peuvent ensuite être intégrés à des modèles, afinde prévoir au mieux, le comportement hydrodynamique de ces aquifères.Cette approche a été appliquée au karst dit de Bourbouillet (sudArdèche, France), afin d’évaluer les possibilités de captages. Les résultats,associés à ceux issus des méthodes hydrochimiques et des tests detraçages, permettent de proposer un modèle de gestion de cet aquifère

Mechanisms, Upscaling, and Prediction of Anomalous Dispersion in Heterogeneous Porous Media

We study the upscaling and prediction of large-scale solute dispersion in heterogeneous porous media with focus on preasymptotic or anomalous features such as tailing in breakthrough curves and spatial concentration profiles as well as nonlinear evolution of the spatial variance of the concentration distribution. Spatial heterogeneity in the hydraulic medium properties is represented in a stochastic modeling approach. Direct numerical Monte Carlo simulations of flow and advective particle motion combined with a Markov model for streamwise particle velocities give insight in the mechanisms of preasymptotic and asymptotic solute transport in terms of the statistical signatures of the medium and flow heterogeneity. Based on the representation of equidistantly sampled particle velocities as a Markov process, we derive an upscaled continuous time random walk approach that can be conditioned on the flow velocities and thus hydraulic conductivity in the injection region. In this modeling framework, we identify the Eulerian velocity distribution, advective tortuosity, and the correlation length of particle velocities as the key quantities for large-scale transport prediction. Thus, the upscaled model predicts the spatial concentration profiles, their first and second centered moments, and the breakthrough curves obtained from direct numerical Monte Carlo simulations in spatially heterogeneous conductivity fields. The presented approach allows to relate the medium and flow properties to large-scale preasymptotic and asymptotic solute dispersion. ©2019. American Geophysical Union. All Rights Reserved.The research leading to these results has received funding from the European Research Council under the European Union's Seventh Framework Programme (FP7/2007‐2013) ERC Grant Agreement 617511 (MHetScale). The data presented in the paper can be accessed at the GitLab ( https://gitlab.com/marco.dentz/darcy‐simulations‐data ).Peer reviewe

Inspection des conduites d’eau potable par sonde autonome à centrale inertielle et transducteurs.

International audienc

Teaching groundwater flow processes: connecting lecture to practical and field classes

International audiencePreparing future hydrogeologists to assess local and regional hydrogeological changes and issues related to water supply is a challenging task that creates a need for effective teaching frameworks. The educational literature suggests that hydrogeology courses should consistently integrate lecture class instructions with practical and field classes. However, most teaching examples still separate these three class components. This paper presents an introductory course to groundwater flow processes taught at Université Montpel-lier 2, France. The adopted pedagogical scheme and the proposed activities are described in details. The key points of the proposed scheme for the course are: (i) iterations into the three class components to address groundwater flow processes topics, (ii) a course that is structured around a main thread (well testing) present in each class component, and (iii) a pedagogical approach that promotes active learning strategies, in particular using original practical classes and field experiments. The experience indicates that the proposed scheme improves the learning process, as compared to a classical , teacher-centered approach

Dataset on onshore groundwaters and offshore submarine spring of a Mediterranean karst aquifer during flow reversal and saltwater intrusion

Groundwater from various shallow and deep reservoirs converges in interaction with marine waters into the limestone aquifer of the Balaruc peninsula (Thau lagoon, southern France). This aquifer faces temporary phenomena of marine water intrusion through the Vise submarine spring located at −29.5 m below the lagoon level. Since the 1960s, seven flow reversal phenomena have occurred, the last one occurring between 11/28/2020 and 03/14/2022. During these phenomena, which can last from a few weeks to several months, the salty water is absorbed from the lagoon to the conduit of the submarine spring, which leads to the salinization of the underlying karst aquifer. The monitoring of flow, water specific conductivity and water temperature data from the karst submarine spring is a key element of the research project to understand the hydrogeological functioning of the karst aquifer under normal conditions or during flow reversal periods. This monitoring allows the characterization of the (in- or out-) flows at the submarine spring, the evaluation of the volume or mass balances, the identification of the hydrogeological and physico-chemical responses (water temperature, specific conductivity) observed within the karstic aquifer. Here, we present the means implemented offshore to acquire data at the submarine spring over the 06/25/2019 - 12/31/2022 time period together with lagoon water's physico-chemical parameters and levels and onshore groundwater's physico-chemical parameters and levels acquired at springs and boreholes from the karst aquifer

XLKarst, uma ferramenta em Excel para análise de series temporais, análise de curva de recessão da fonte e classificação de aquíferos cársticos

Karst aquifers are complex hydrogeological systems that require numerous in-situ measurements of hydrological and physico-chemical parameters to characterize transfer processes from the recharge area to the karst spring. Numerous graphical, statistical or signal processing methods have been developed for decades to interpret these measurements, but there is no simple and standardized tool that can be used for this purpose, which is necessary for a rigorous comparison of results between case studies. This Technical Note presents XLKarst, which has been developed to provide a simple and easy-to-use tool to process a selection of proven methods that characterize the functioning of karst systems. This tool allows (i) time series analysis based on correlation and spectral analysis and, for flow measurements, the use of other statistics and base flow separation, (ii) calculation of the cumulative distribution function to build a spring flow probability plot, and (iii) analysis of spring flow recession and expression of the results in a karst system classification scheme. These methods are first described by providing the key elements of their use and interpretation in the scientific literature. Then, an application to the Fontaine de Nîmes karst system (southern France) is used to highlight the complementarity of the methods proposed by XLKarst to describe the hydrodynamic behavior of a karst system based on daily data of rainfall and discharge over 22 years.Resumen Los acuíferos kársticos son sistemas hidrogeológicos complejos que requieren numerosas mediciones in situ de parámetros hidrológicos y fisicoquímicos para caracterizar los procesos de transferencia desde la zona de recarga hasta el manantial kárstico. Durante décadas se han desarrollado numerosos métodos gráficos, estadísticos o de procesamiento de señales para interpretar estas mediciones, pero no existe ninguna herramienta sencilla y estandarizada que pueda utilizarse con este fin, lo cual es necesario para una comparación rigurosa de los resultados entre casos de estudio. Esta Nota Técnica presenta XLKarst, que se ha desarrollado para proporcionar una herramienta sencilla y fácil de usar para procesar una selección de métodos probados que caracterizan el funcionamiento de los sistemas kársticos. Esta herramienta permite (i) el análisis de series temporales basado en la correlación y el análisis espectral y, para las mediciones de caudal, el uso de otros estadísticos y la separación del caudal base, (ii) el cálculo de la función de distribución acumulativa para construir un gráfico de probabilidad del caudal de manantial, y (iii) el análisis de la recesión del caudal de manantial y la expresión de los resultados en un esquema de clasificación de sistemas kársticos. Estos métodos se describen primero proporcionando los elementos clave de su uso e interpretación en la literatura científica. A continuación, se utiliza una aplicación al sistema kárstico de Fontaine de Nîmes (sur de Francia) para poner de relieve la complementariedad de los métodos propuestos por XLKarst para describir el comportamiento hidrodinámico de un sistema kárstico a partir de datos diarios de precipitación y descarga a lo largo de 22 años.Résumé Les aquifères karstiques sont des systèmes hydrogéologiques complexes qui nécessitent de nombreuses mesures in-situ de paramètres hydrologiques et physico-chimiques pour caractériser les processus de transfert de la zone de recharge à la source karstique. De nombreuses méthodes graphiques, statistiques ou de traitement du signal ont été développées depuis des décennies pour interpréter ces mesures, mais il n'existe pas d'outil simple et standardisé pouvant être utilisé à cette fin, ce qui est nécessaire pour une comparaison rigoureuse des résultats entre les études de cas. Cette note technique présente XLKarst, qui a été développé pour fournir un outil simple et facile à utiliser pour traiter une sélection de méthodes éprouvées qui caractérisent le fonctionnement des systèmes karstiques. Cet outil permet (i) l'analyse de séries temporelles basée sur la corrélation et l'analyse spectrale et, pour les mesures de débit, l'utilisation d'autres statistiques et la séparation du débit de base, (ii) le calcul de la fonction de distribution cumulative pour construire un graphique de probabilité de débit de source, et (iii) l'analyse de la récession du débit de source et l'expression des résultats dans un schéma de classification des systèmes karstiques. Ces méthodes sont d'abord décrites en fournissant les éléments clés de leur utilisation et de leur interprétation dans la littérature scientifique. Ensuite, une application au système karstique de la Fontaine de Nîmes (sud de la France) est utilisée pour mettre en évidence la complémentarité des méthodes proposées par XLKarst pour décrire le comportement hydrodynamique d'un système karstique basé sur des données journalières de précipitations et de débits sur une période de 22 ans.Resumo Aquíferos cárstico são sistemas hidrogeológicos complexos que requerem inúmeras medições in-situ de parâmetros hidrológicos e físico-químicos para caracterizar os processos de transferência da área de recarga para a fonte cárstica. Inúmeros métodos de processamento gráfico, estatístico ou de sinal foram desenvolvidos por décadas para interpretar estas medições, mas não há uma ferramenta simples e padronizada que pode ser utilizada para este propósito, que é necessário para a comparação rigorosa dos resultados entre estudos de caso. Esta Nota Técnica apresenta XLKarst, que tem sido desenvolvido para fornecer uma ferramenta simples e fácil de utilizar para processar uma seleção de métodos comprovados que caracterizam o funcionamento de um sistema cárstico. Essa ferramenta permite (i) Análise de séries temporais baseada na correlação e análise espectral e, para medidas de fluxo, o uso de outros estatísticas baseadas na separação de fluxo, (ii) cálculo da função de distribuição cumulativa para construção de gráfico de probabilidade de fluxo da fonte e (iii) análise do fluxo de recessão da fonte e expressão dos resultados em um esquema de classificação de sistemas cárstico. Estes métodos são primeiramente descritos fornecendo os elementos chave de seu uso e interpretação na literatura científica. Em seguida, a aplicação no sistema cárstico de Fontaine de Nimes (sul da França) é usada para exaltar a complementariedade dos métodos propostos pelo XLKarst para descrever o comportamento hidrodinâmico do sistema cárstico baseado em dados diários de precipitação e descarga ao longo de 22 anos

Understanding the Radial Force of Stroke Thrombectomy Devices to Minimize Vessel Wall Injury: Mechanical Bench Testing of the Radial Force Generated by a Novel Braided Thrombectomy Assist Device Compared to Laser-Cut Stent Retrievers in Simulated MCA Vessel Diameters

Background: Recent reports have raised various concerns about the risk of vessel wall injury while withdrawing current laser-cut stent retrievers during active strut apposition to the vessel walls. The development of braided thrombectomy assist devices in conjunction with aspiration systems may be gentler on the fragile brain vessels and more optimized with regard to the radial force (RF) for vessel diameters of proximal (M1) and distal (M2) large vessel occlusions (LVOs). Methods: Mechanical bench testing of the RF was performed using a radial compression station mounted on a tensile testing machine. The total RF in newtons (N) generated in vessels with diameters ranging from 2.25 to 3 mm as seen in proximal LVOs (∼M1), and in vessel diameters ranging from 1.5 to 2.24 mm as seen in distal LVOs (∼M2), was measured. The outer diameter of each stent was recorded, and an RF ≤1 N was grouped as low, while an RF \u3e1 N was grouped as high for this analysis. Results: The total RFs of all laser-cut stent retrievers were all higher in the simulated M2 vessels (\u3e1 N) than in the M1 vessels (\u3c1 N), whereas the total RFs of the braided thrombectomy assist devices were uniformly low in both the simulated M1 and the simulated M2 vessels. Conclusions: Novel braided thrombectomy assist devices in conjunction with aspiration systems have lower RFs than existing laser-cut stent retrievers in M1 and M2 vessel diameters. Further in vivo studies are needed to delineate the impact of lowering the RF on vessel wall integrity