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Jeannin, Pierre-Yves

Nom
Jeannin, Pierre-Yves
Affiliation principale
Email
pierre-yves.jeannin@unine.ch
Identifiants
https://libra.unine.ch/handle/123456789/809

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  • Publication
    Accès libre
    The role of tributary mixing in chemical variations at a karst spring, Milandre, Switzerland
    (2007-01-01)
    Perrin, J.
    ;
    Jeannin, Pierre-Yves 
    ;
    Cornaton, Fabien 
    Solute concentration variations during flood events were investigated in a karst aquifer of the Swiss Jura. Observations were made at the spring, and at the three main subterraneous tributaries feeding the spring. A simple transient flow and transport numerical model was able to reproduce chemographs and hydrographs observed at the spring, as a result of a mixing of the concentration and discharge of the respective tributaries. Sensitivity analysis carried out with the model showed that it is possible to produce chemical variations at the spring even if all tributaries have constant (but different for each of them) solute concentrations. This process is called tributary mixing. The good match between observed and modelled curves indicate that, in the phreatic zone, tributary mixing is probably an important process that shapes spring chemographs. Chemical reactions and other mixing components (e.g. from low permeability volumes) have a limited influence.
    Dissolution-related (calcium, bicarbonate, specific conductance) and pollution-related parameters (nitrate, chloride, potassium) displayed slightly different behaviours: during moderate flood events, the former showed limited variations compared to the latter. During large flood events, both presented chemographs with significant changes. No significant event water participates in moderate flood events and tributary mixing will be the major process shaping chemographs. Variations are greater for parameters with higher spatial variability (e.g. pollution-related). Whereas for large flood events, the contribution of event water becomes significant and influences the chemographs of all the parameters. As a result, spring water vulnerability to an accidental pollution is low during moderate flood events and under base flow conditions. It strongly increases during large flood events, because event water contributes to the spring discharge.
  • 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.
  • Publication
    Accès libre
    Implications of the spatial variability of infiltration-water chemistry for the investigation of a karst aquifer: a field study at Milandre test site, Swiss Jura
    (2003)
    Perrin, J.
    ;
    Jeannin, Pierre-Yves 
    ;
    Zwahlen, François 
    Le site test de Milandre est un aquifère karstique idéal pour étudier lhétérogénéité spatiale des éléments chimiques majeurs car de nombreux points dobservation sont accessibles : source, rivière souterraine et affluents, forages à différentes profondeurs. Les principales causes de la variabilité spatiale des paramètres chimiques sont : nature et localisation des intrants, la structure de la zone dinfiltration, la réactivité des paramètres (temps de transit vs. cinétique de réaction) et le mélange des eaux. Les chimiogrammes observés à la source du système karstique représentent la somme de cette hétérogénéité spatiale. Il est de fait difficile, pour un tel aquifère, dinterpréter la réponse chimique globale en termes de mélanges deau des différents sous-systèmes de laquifère (ruissellement, réservoir matriciel, épikarst). Les éléments chimiques correspondant aux intrants agricoles montrent des variations saisonnières relativement importantes (Coefficient de variation denviron 15%) alors que les paramètres liés à la pluie (δ18O) et à laquifère (Ca2+, HCO3–) présentent des variations de quelques pour cents. Un tel résultat indique un stockage deau dau minimum quelques mois dans lépikarst., The Milandre test site is an ideal karstic aquifer for studying the spatial heterogeneity of groundwater chemistry. Numerous observation points can be sampled: the spring, the underground river and its tributaries, and boreholes at different depths. The main causes of the spatial variability of the chemical parameters are: nature and localisation of the input, the structure of the infiltration zone, chemical reactions (transit time vs. reaction kinetics) and mixing of different waters. Physico-chemical data on springs discharging from the karstic system represent the sum of this spatial heterogeneity. Therefore, it is difficult to interpret the global-chemical response with a simple mixing model of the aquifer subsystems (runoff, matrix reservoir, epikarst). Chemical constituents related to agricultural inputs show important seasonal variations (coefficient of variation approximately 15%) and parameters linked to rainfall (δ18O) and to the aquifer (Ca2+, HCO3–) present variations of less than 5%. This result indicates the importance of water storage in the epikarstic aquifer for periods of a few months., La zona de ensayos de Milandre (Suiza) es un acuífero kárstico ideal para estudiar la heterogeneidad especial de la química de las aguas subterráneas. Se puede muestrear numerosos puntos de observación, incluyendo manantiales, ríos subterráneos y sus tributarios, y sondeos a diferentes profundidades. Las causas principales de la variabilidad espacial de los parámetros químicos son las siguientes: naturaleza y localización de la entrada, estructura de la zona de infiltración, reacciones químicas (tiempo de tránsito versus la cinética de las reacciones), y mezcla de aguas diferentes. Los gráficos hidroquímicos de los manantiales en el sistema kárstico representan la suma de esta heterogeneidad espacial. Por tanto, es difícil interpretar la respuesta química global con un modelo de mezcla simple de los subsistemas acuíferos (escorrentía, reservorio de la matriz, epikarst). Los parámetros asociados a aportaciones de origen agrícola muestran variaciones estacionales importantes, con un coeficiente de variación en torno al 5%, mientras que los parámetros vinculados a la precipitación (δ18O) y al acuífero (calcio, bicarbonato) presentan variaciones inferiores al 5%. Este resultado indica que se produce un almacenamiento importante de agua durante un par de meses en el acuífero epikárstico.