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Zwahlen, François

Nom
Zwahlen, François
Affiliation principale
Fonction
Professeur.e émérite
Email
francois.zwahlen@unine.ch
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https://libra.unine.ch/handle/123456789/147

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  • Publication
    Accès libre
    Differential Transport of Atrazine and Glyphosate in Undisturbed Sandy Soil Column
    (2010)
    Zhou, Yu
    ;
    Wang, Y.
    ;
    Hunkeler, Daniel 
    ;
    Zwahlen, François 
    ;
    Boillat, J.
    With increasing awareness and concern for environmental quality, it is important to study the fate of pesticides in the subsurface. Laboratory studies were conducted to determine the behavior of atrazine and glyphosate within the root zone of an undisturbed sandy soil in Jianghan Plain, central China. Chloride as a tracer for water movement was applied to the soil as KCl for 26 hours before pesticide application for another 160 hours. Glyphosate, atrazine, and Cl concentrations (conc.) were determined as a function of time in breakthrough curves (BTCs). Atrazine BTC was fitted better in convection-dispersion equation equilibrium model. For glyphosate, however, a two-site non-equilibrium model was chosen. Leaching rate of atrazine from sandy soil was much higher than that of glyphosate and it took longer for glyphosate to leach through the column due to stronger sorption and degradation to its major metabolite, AMPA (aminomethylphosphonic acid, CH6NO3P), which was detected (up to 8890 ng/l) in the final leachate.
  • Publication
    Métadonnées seulement
    Percolation and Particle Transport in the Unsaturated Zone of a Karst Aquifer
    (2009)
    Pronk, Michiel 
    ;
    Goldscheider, Nico
    ;
    Zopfi, Jakob 
    ;
    Zwahlen, François 
    Recharge and contamination of karst aquifers often occur via the unsaturated zone, but the functioning of this zone has not yet been fully understood. Therefore, irrigation and tracer experiments, along with monitoring of rainfall events, were used to examine water percolation and the transport of solutes, particles, and fecal bacteria between the land surface and a water outlet into a shallow cave. Monitored parameters included discharge, electrical conductivity, temperature, organic carbon, turbidity, particle-size distribution (PSD), fecal indicator bacteria, chloride, bromide, and uranine. Percolation following rainfall or irrigation can be subdivided into a lag phase (no response at the outlet), a piston-flow phase (release of epikarst storage water by pressure transfer), and a mixed-flow phase (increasing contribution of freshly infiltrated water), starting between 20 min and a few hours after the start of recharge event. Concerning particle and bacteria transport, results demonstrate that (1) a first turbidity signal occurs during increasing discharge due to remobilization of particles from fractures (pulse-through turbidity); (2) a second turbidity signal is caused by direct particle transfer from the soil (flow-through turbidity), often accompanied by high levels of fecal indicator bacteria, up to 17,000 Escherichia coli/100 mL; and (3) PSD allows differentiation between the two types of turbidity. A relative increase of fine particles (0.9 to 1.5 mu m) coincides with microbial contamination. These findings help quantify water storage and percolation in the epikarst and better understand contaminant transport and attenuation. The use of PSD as "early-warning parameter" for microbial contamination in karst water is confirmed.
  • Publication
    Accès libre
    Percolation and Particle Transport in the Unsaturated Zone of a Karst Aquifer
    (2008)
    Pronk, Michiel 
    ;
    Goldscheider, Nicola
    ;
    Zopfi, Jakob 
    ;
    Zwahlen, François 
    Recharge and contamination of karst aquifers often occur via the unsaturated zone, but the functioning of this zone has not yet been fully understood. Therefore, irrigation and tracer experiments, along with monitoring of rainfall events, were used to examine water percolation and the transport of solutes, particles, and fecal bacteria between the land surface and a water outlet into a shallow cave. Monitored parameters included discharge, electrical conductivity, temperature, organic carbon, turbidity, particle-size distribution (PSD), fecal indicator bacteria, chloride, bromide, and uranine. Percolation following rainfall or irrigation can be subdivided into a lag phase (no response at the outlet), a piston-flow phase (release of epikarst storage water by pressure transfer), and a mixed-flow phase (increasing contribution of freshly infiltrated water), starting between 20 min and a few hours after the start of recharge event. Concerning particle and bacteria transport, results demonstrate that (1) a first turbidity signal occurs during increasing discharge due to remobilization of particles from fractures (pulse-through turbidity); (2) a second turbidity signal is caused by direct particle transfer from the soil (flow-through turbidity), often accompanied by high levels of fecal indicator bacteria, up to 17,000 Escherichia coli/100 mL; and (3) PSD allows differentiation between the two types of turbidity. A relative increase of fine particles (0.9 to 1.5 μm) coincides with microbial contamination. These findings help quantify water storage and percolation in the epikarst and better understand contaminant transport and attenuation. The use of PSD as "early-warning parameter" for microbial contamination in karst water is confirmed.
  • Publication
    Accès libre
    Groundwater protection in fractured media: a vulnerability-based approach for delineating protection zones in Switzerland
    (2008)
    Pochon, Alain
    ;
    Tripet, Jean-Pierre
    ;
    Kozel, Ronald
    ;
    Meylan, Benjamin
    ;
    Sinreich, Michael
    ;
    Zwahlen, François 
    Une approche basée sur le concept de vulnérabilité a été développée pour délimiter les zones de protection des sources d’eau souterraine en milieu fissuré. Elle permet l’application de la réglementation suisse concernant la protection des eaux. La diversité des conditions hydrogéologiques propre aux aquifères fissurés est prise en compte par l’application de solutions spécifiques pour chaque type de contexte. Un processus décisionnel permet de sélectionner une des trois méthodes en fonction de la vulnérabilité de la source et de l’hétérogénéité de l’aquifère. L’approche requiert tout d’abord une évaluation de la vulnérabilité de la source comprenant un suivi des hydrogrames et de la qualité de l’eau. En cas de faible vulnérabilité de la source, une méthode simplifiée basée sur la prise en compte d’une distance minimale est appliquée (“Méthode des distances”). Pour les sources vulnérables, une deuxième étape d’investigation est nécessaire pour mieux caractériser l’aquifère, principalement en terme d’hétérogénéité. Cette deuxième étape comprend une étude hydrogéologique détaillée et des essais de traçage. Si l’aquifère apparaît peu hétérogène, les zones de protection sont délimitées sur la base d’isochrones (“Méthode des isochrones”). En cas de forte hétérogénéité, une méthode de cartographie de la vulnérabilité des eaux souterraines est appliquée (“méthode DISCO”), basée sur l’évaluation des paramètres “discontinuité”, “couverture protectrice” et “ruissellement”. Chaque méthode est illustrée par un exemple d’application., Für Quellfassungen in Kluftgesteinen wurde ein Verfahren zur Bemessung von Grundwasserschutzzonen entwickelt, welches der Umsetzung der schweizerischen Gewässerschutzverordnung dient. Es beruht auf dem Konzept der Vulnerabilität und berücksichtigt die geologische und hydrogeologische Vielfalt von Kluft-Grundwasserleitern. Mittels eines Entscheidungsprozesses kann von drei unterschiedlichen Methoden diejenige ausgewählt werden, welche der Vulnerabilität der Quellfassung und der Heterogenität des Grundwasserleiters am besten entspricht. Zunächst wird dabei die Vulnerabilität der Quelle bestimmt, basierend auf Hydrogrammen und Beobachtung der Wasserqualität. Bei gering vulnerablen Quellen können die Schutzzonen direkt mit einer Mindestausdehnung ausgeschieden werden („Distanz-Methode“). Für vulnerable Quellen sind zusätzliche Untersuchungen notwendig, um die Eigenschaften des Grundwasserleiters – insbesondere dessen Heterogenität – besser zu erfassen. Dieser zweite Schritt beinhaltet hydrogeologische Detailstudien inklusive Markierversuche. Bei schwach heterogenen Kluft-Grundwasserleitern werden die Schutzzonen dann mittels Isochronen bemessen („Isochronen-Methode“). Die aufwendigste Methode gelangt nur bei einem stark heterogenen Grundwasserleiter zur Anwendung („Methode DISCO“). Sie basiert auf einer Kartierung der Trennflächen des Kluft-Grundwasserleiters, der schützenden Deckschichten sowie des Oberflächenabflusses, und erfasst damit die Vulnerabilität des Einzugsgebietes. Jede der drei Methoden wird anhand eines Fallbeispiels erläutert., A vulnerability-based approach for delineating groundwater protection zones around springs in fractured media has been developed to implement Swiss water-protection regulations. It takes into consideration the diversity of hydrogeological conditions observed in fractured aquifers and provides individual solutions for each type of setting. A decision process allows for selecting one of three methods, depending on the spring vulnerability and the heterogeneity of the aquifer. At the first stage, an evaluation of spring vulnerability is required, which is essentially based on spring hydrographs and groundwater quality monitoring. In case of a low vulnerability of the spring, a simplified method using a fixed radius approach (“distance method”) is applied. For vulnerable springs, additional investigations must be completed during a second stage to better characterize the aquifer properties, especially in terms of heterogeneity. This second stage includes a detailed hydrogeological survey and tracer testing. If the aquifer is assessed as slightly heterogeneous, the delineation of protection zones is performed using a calculated radius approach based on tracer test results (“isochrone method”). If the heterogeneity is high, a groundwater vulnerability mapping method is applied (“DISCO method”), based on evaluating discontinuities, protective cover and runoff parameters. Each method is illustrated by a case study., Se ha desarrollado una aproximación basada en la vulnerabilidad para definir zonas de protección de aguas subterráneas en torno a manantiales con el objeto de implementar las normas de protección de Suiza. Se toma en consideración la diversidad de condiciones hidrogeológicas observadas en acuíferos fracturados y provee soluciones individuales para cada tipo de escenario. Un proceso de decisión permite seleccionar uno de tres métodos, dependiendo de la vulnerabilidad de los manantiales y de la heterogeneidad del acuífero. La primera etapa requiere de una evaluación de la vulnerabilidad del manantial, que esencialmente se basa en hidrogramas del manantial y en datos de monitoreo de la calidad del agua subterránea. Si el manantial es de baja vulnerabilidad, se aplica un método simplificado que utiliza una aproximación de radio fijo (“Método de la Distancia”). Para manantiales vulnerables, en una segunda etapa deben completarse investigaciones adicionales para caracterizar más adecuadamente las propiedades del acuífero, especialmente su heterogeneidad. Esta segunda etapa incluye un reconocimiento hidrogeológico detallado y ensayos de trazadores. Si se juzga que el acuífero es altamente heterogéneo, la determinación de zonas de protección utiliza una aproximación del radio calculado a partir de ensayos de trazadores (“Método de Isocronas”). Si la heterogeneidad es alta, se aplica un método de mapeo de la vulnerabilidad del acuífero (“Método DISCO”), que se basa en la evaluación de discontinuidades, cubierta de protección y parámetros del escurrimiento superficial. Cada método se ilustra con un caso de estudio., Per delimitare le zone di protezione delle acque sotterranee relative alle sorgenti in acquiferi fessurati è stato sviluppato un metodo basato sul concetto di vulnerabilità. Tale approccio consente l’applicazione della normativa svizzera in materia di protezione delle acque. Si tiene conto in particolare della diversità delle condizioni idrogeologiche che caratterizzano gli acquiferi fessurati mediante l’applicazione di soluzioni specifiche per i diversi contesti. Un processo decisionale permette di selezionare uno dei tre metodi elaborati, in funzione della vulnerabilità della sorgente e dell’eterogeneità dell’acquifero. L’approccio metodologico richiede innanzitutto una valutazione della vulnerabilità della sorgente. Tale valutazione comporta un controllo degli idrogrammi e della qualità dell’acqua. In caso di bassa vulnerabilità della sorgente, si applica un metodo semplificato, che prevede il rispetto di una distanza minima (“metodo delle distanze”). Per le sorgenti vulnerabili sono necessarie altre indagini, volte a definire meglio le caratteristiche dell’acquifero, soprattutto per quanto concerne l’eterogeneità. Questa seconda fase comprende uno studio idrogeologico dettagliato e prove di tracciamento. In caso di bassa eterogeneità dell’acquifero, le zone di protezione sono delimitate sulla base di isocrone (“metodo delle isocrone”). In caso di forte eterogeneità, si applica invece un metodo cartografico per determinare la vulnerabilità delle acque sotterranee (“metodo DISCO”), basato sulla valutazione dei seguenti parametri: “discontinuità”, “copertura di protezione” e “ruscellamento”. Ogni metodo è illustrato da un esempio concreto.
  • Publication
    Métadonnées seulement
    Karst groundwater protection: First application of a Pan-European Approach to vulnerability, hazard and risk mapping in the Sierra de Libar (Southern Spain)
    (2006)
    Andreo, Bartolomé
    ;
    Goldscheider, Nico
    ;
    Vadillo, Iñaki
    ;
    Vias, Jesús María
    ;
    Neukum, Christoph
    ;
    Sinreich, Michael
    ;
    Jimenez, Pablo
    ;
    Brechenmacher, Julia
    ;
    Carrasco, Francisco
    ;
    Hotzl, Heinz
    ;
    Perles, María Jesús
    ;
    Zwahlen, François 
    The European COST action 620 proposed a comprehensive approach to karst groundwater protection, comprising methods of intrinsic and specific vulnerability mapping, validation of vulnerability maps, hazard and risk mapping. This paper presents the first application of all components of this Pan-European Approach to the Sierra de Libar, a karst hydrogeology system in Andalusia, Spain. The intrinsic vulnerability maps take into account the hydrogeological characteristics of the area but are independent from specific contaminant properties. Two specific vulnerability maps were prepared for faecal coliforrns and BTEX These maps take into account the specific properties of these two groups of contaminants and their interaction with the karst hydrogeological system. The vulnerability assessment was validated by means of tracing tests, hydrological, hydrochemical and isotope methods. The hazard map shows the localization of potential contamination sources resulting from human activities, and evaluates those according to their dangerousness. The risk of groundwater contamination depends on the hazards and the vulnerability of the aquifer system. The risk map for the Sierra de Libar was thus created by overlaying the hazard and vulnerability maps. (C) 2005 Elsevier B.V. All rights reserved.
  • Publication
    Accès libre
    Karst groundwater protection: First application of a Pan-European Approach to vulnerability, hazard and risk mapping in the Sierra de Líbar (Southern Spain)
    (2006)
    Andreo, Bartolomé
    ;
    Goldscheider, Nicola
    ;
    Vadillo, Iñaki
    ;
    Vías, Jesús María
    ;
    Neukum, Christoph
    ;
    Sinreich, Michael
    ;
    Jiménez, Pablo
    ;
    Brechenmacher, Julia
    ;
    Carrasco, Francisco
    ;
    Hötzl, Heinz
    ;
    Perles, María Jesús
    ;
    Zwahlen, François 
    The European COST action 620 proposed a comprehensive approach to karst groundwater protection, comprising methods of intrinsic and specific vulnerability mapping, validation of vulnerability maps, hazard and risk mapping. This paper presents the first application of all components of this Pan-European Approach to the Sierra de Líbar, a karst hydrogeology system in Andalusia, Spain. The intrinsic vulnerability maps take into account the hydrogeological characteristics of the area but are independent from specific contaminant properties. Two specific vulnerability maps were prepared for faecal coliforms and BTEX. These maps take into account the specific properties of these two groups of contaminants and their interaction with the karst hydrogeological system. The vulnerability assessment was validated by means of tracing tests, hydrological, hydrochemical and isotope methods. The hazard map shows the localization of potential contamination sources resulting from human activities, and evaluates those according to their dangerousness. The risk of groundwater contamination depends on the hazards and the vulnerability of the aquifer system. The risk map for the Sierra de Líbar was thus created by overlaying the hazard and vulnerability maps.
  • Publication
    Accès libre
    Identification of zones of preferential groundwater tracer transport using a mobile downhole fluorometer
    (2005)
    Flynn, Raymond Matthew
    ;
    Schnegg, Pierre-André 
    ;
    Costa, Roberto 
    ;
    Mallen, German
    ;
    Zwahlen, François 
    Un fluorimètre a été utilisé pour détecter les zones découlement préférentiel dun traceur dans un puits dobservation. Les identifications de telles zones nest pas possible si les échantillons individuels sont collectés sur toute les longueurs des parties crépinées du puits. Les tests de laboratoire utilisant un fluorimètre et un dispositif adéquat ont montré que les fluorimètres pouvaient servir à définir les régimes découlement de leau dans les puits. Durant les investigations de terrain dans un aquifère poreux, le fluorimètre a enregistré les concentrations du traceur dans un puits dobservation avec une crépine de 12 m. de long, 10 m sous le gradient hydraulique dans un puits à pénétration totale. Les résultats des tests ont montré que le traceur apparaissait dans un interval discret de 2.5 m de long. Un test de dilution en puits unique et des données découlement vertical ont indiqué que leau rentrait dans le puits à dautres profondeurs, mais le traceur na pas été détecté à ces niveaux. Un modèle numérique reproduisant le test de dilution et le profil de concentration a indiqué que leau entrait dans le puits à ces niveaux à des vitesses comparables de celle du traceur. Ces données suggèrent que lécoulement des eaux souterraines varie avec la profondeur dans laquifère sous la zone dinvestigation. Dailleurs, les simulations de larrivée du traceur ont montré que la distribution des concentrations du traceur dans le puits ne pouvaient pas être dues à une couche plus fine que 0.5 m., A mobile downhole fluorometer was used to detect zones of preferential groundwater tracer transport into an observation well. Identification of such zones is not possible if individual samples are collected over the wells entire screened interval. Laboratory-based tests using the fluorometer, and a purpose-built apparatus demonstrated that the fluorometer could be used with tracers to characterise well water flow regimes. During field investigations in a porous aquifer, the fluorometer monitored tracer concentrations in an observation well with a 12-m-long screen, 10 m down the hydraulic gradient from a fully penetrating injection well. Test results showed that the tracer occurred in the observation well over a discrete 2.5-m-thick interval. Single-well dilution test and vertical-flow data indicated that water entered the well at additional depths, but no tracer was detected at these levels. A numerical model reproducing dilution test concentration profiles indicated that water entered the well in many of these horizons at comparable velocities to those in the tracer-bearing zone. These data suggest that groundwater flow direction varied with depth in the aquifer under investigation. Moreover, simulations of tracer arrival indicated that the tracer distribution observed in the observation well was derived from a horizon that may be no thicker than 0.5 m., Se utilizó un fluorómetro móvil descendente para detectar zonas de transporte preferencial de trazadores de agua subterránea en un pozo de observación. La identificación de tales zonas no es posible si se colectan muestras individuales en todo el intervalo enmallado del pozo. En base a pruebas de laboratorio utilizando el fluorómetro y un aparato especial construido se demostró que el fluorómetro podría utilizarse con trazadores para caracterizar ambientes de flujo de agua en los pozos. Durante investigaciones de campo en un acuífero poroso, el fluorómetro monitoreó concentraciones de trazadores en un pozo de observación con una malla de 12 m de largo, 10 m abajo del gradiente hidráulico de un pozo de inyección que penetra totalmente el acuífero. Los resultados de las pruebas muestran que el trazador se presentó en el pozo de observación en un intervalo discreto de 2.5 m de espesor. Pruebas de dilución en un solo pozo y datos de flujo vertical indicaron que el agua entró al. pozo en profundidades adicionales, pero que no se detectó el trazador en esos niveles. Un modelo numérico que reproduce los perfiles de concentración de las pruebas de dilución indica que el agua entró al. pozo en muchos de estos horizontes en velocidades comparables a las existentes en la zona portadora de trazadores. Estos datos sugieren que la dirección de flujo de agua subterránea varió con la profundidad en el acuífero bajo investigación. Por otra parte, las simulaciones de llegada del trazador indicaron que la distribución del trazador observada en el pozo de observación se derivó de un horizonte cuyo espesor puede no ser mayor de 0.5 m.
  • Publication
    Accès libre
    Vulnerability assessment in karstic areas: validation by field experiments
    (2004)
    Perrin, J.
    ;
    Pochon, Alain
    ;
    Jeannin, Pierre-Yves 
    ;
    Zwahlen, François 
    Several methods have been developed for vulnerability mapping in karstic areas. These methods need additional validation by field experiments. Several tests have been carried out in the Swiss Jura with natural and artificial tracers. The protective role of some intrinsic properties of the system, such as glacial deposits covering karst, epikarst storage and system dilution effect, have been clearly demonstrated. Use of three tracers in parallel showed the reactivity of the epikarst: all tracers arrived at the same time, but their relative concentration stayed clearly different. A classification of contamination scenarios into four classes is proposed. It is shown that the relevance of some intrinsic properties depends on the considered scenario class. The hydrodynamic state of the aquifer influences greatly flow velocities and can strongly modify contaminant concentrations at the output of the system. The spatial repartition (point vs diffuse) and the quantity of contaminant entering the system will also influence the output response. Hence, results from tracing experiments cannot be used straightforward for obtaining a representative value of flow velocity, dispersion or recovery rate.