Résultat de la recherche
Serological signature of tick-borne pathogens in Scandinavian brown bears over two decades
Background: Anthropogenic disturbances are changing the geographic distribution of ticks and tick-borne diseases. Over the last few decades, the tick Ixodes ricinus has expanded its range and abundance considerably in northern Europe. Concurrently, the incidence of tick-borne diseases, such as Lyme borreliosis and tick-borne encephalitis, has increased in the human populations of the Scandinavian countries. Methods: Wildlife populations can serve as sentinels for changes in the distribution of tick-borne diseases. We used serum samples from a long-term study on the Scandinavian brown bear, Ursus arctos, and standard immunological methods to test whether exposure to Borrelia burgdorferi sensu lato, the causative agent of Lyme borreliosis, and tick-borne encephalitis virus (TBEV) had increased over time. Bears had been sampled over a period of 18 years (1995-2012) from a southern area, where Ixodes ricinus ticks are present, and a northern area where ticks are uncommon or absent. Results: Bears had high levels of IgG antibodies against B. burgdorferi sensu lato but not TBEV. Bears at the southern area had higher values of anti-Borrelia IgG antibodies than bears at the northern area. Over the duration of the study, the value of anti-Borrelia IgG antibodies increased in the southern area but not the northern area. Anti-Borrelia IgG antibodies increased with the age of the bear but declined in the oldest age classes. Conclusions: Our study is consistent with the view that ticks and tick-borne pathogens are expanding their abundance and prevalence in Scandinavia. Long-term serological monitoring of large mammals can provide insight into how anthropogenic disturbances are changing the distribution of ticks and tick-borne diseases.
Notice explicative de la carte hydrogéologique de la Suisse 1: 100'000?Feuille No 6: Sarine/Saane
Circulations profondes des eaux du Continental Terminal (Niger)
Geohydrological parameters identification and groundwater vulnerability to pollution: A Swiss case study
The alluvial aquifer of the Rhône valley in Switzerland, which extends over 110 km and occupies an area of 256 km2, is of great economic importance. Its groundwaters are easily accessible and thus exploitable at low cost. However, its location in an often narrow valley with intense human activity (industry, agriculture, communications network) makes it particularly vulnerable from both a qualitative (industrial and\or agricultural pollution) and quantitative point of view (groundwater flow disturbance following civil engineering works). Since 1995, the Swiss canton of Valais has decided to compile datasets from a number of local studies (water supply, hydro-electricity, and geotechnical studies) into a regional, integrated hydrogeological framework. The realization of the study has shown the importance of GIS tool either for the computing and mapping of the first piezometric map between Brig and Léman Lake or the elaboration of vulnerability maps. The geostatistic tool was also intensively used all over the spatial treatment of data. The comparison of groundwaters NO3-- content (1985 and 1995), has shown that globally the nitrates content in the groundwater is low (< 30 mg/l for 90 % of samples). However it must be notice that the evolution of the NO3-- content degrades during time. The study of vulnerability to pollution for the aquifer situated between Sierre and Vétroz as shown significant differences between the four different methods used. As main results DRASTIC and SINTACS integrated methods are concentrated between Moderate and High vulnerability when NLFB and GOD intrinsic methods are concentrated between Very Low and Moderate vulnerability. Intrinsic methods have the tendency to minimize the vulnerability.
A Statistical analysis of hydro-climatic stress on karst aquifer system (Switzerland)
Impact des changements climatiques sur le comportement des systèmes aquifères
3-D Groundwater Flow Modeling in Heterogeneous Geologic Media: an Integrated Approach Using Spatial and Temporal Database, Geostatistics and GIS
L'objectif de ce travail est de présenter, à travers plusieurs articles et plusieurs approches, l'identification des systèmes hydrogéologiques dans la résolution de problèmes pratiques. Une partie majeure de ce travail montre l'évolution des méthodes et des techniques numériques les plus récentes essentiellement dans l'organisation des données hydrogéologiques spatiales et temporelles, la re-construction des divers champs structuraux et hydrodynamiques jusqu'aux traitement et représentation des résultats des simulations numériques tridimensionnelles des écoulements souterrains par la méthode des éléments finis. Les approches que nous avons utilisées sont globales ou empiriques, déterministes ou stochastiques. La combinaison des techniques des systèmes d'information géographique, de géostatistique, et de simulation numérique déterministe des écoulements souterrains, représente un apport original et indéniable. Cette démarche intégrée du traitement numérique des données spatiales nous a permis de proposer un modèle mathématique 3-D opérationnel, dans la région de Visp (Valais), permettant la gestion des eaux souterraines. De plus, on peut noter trois thèmes abordés à travers les articles intégrés dans la thèse. Le premier traite des aspects de la création d'une base de données tabulaires reliée à un système d'information géographique dans un environnement du karst neuchâtelois. Le second montre les limites des méthodes classiques empiriques dans l'étude de la vulnérabilité des aquifères à la pollution. Le troisième permet d'évaluer l'incertitude des trajectoires en terme de migration de polluant par combinaison de modèles déterministes d'écoulement et des modèles probabilistes
3-D groundwater modeling at regional scale
Large hydrogeological basins are constituted of several superimposed aquifers, separated by geological formations of relatively low permeabilities. The delimitation of the different flow systems is far more difficult to realize for a heterogeneous system. Flux vectors provide valuable indications about groundwater flow paths and hydraulic exchanges between the different geological formations. Hydraulic relationships between two superimposed aquifers can vary locally: an aquifer can «feed» the underlying one at some point and conversely elsewhere. These relationships, which constitute in fact the flow field, will be determined by the structure of the basin as defined by the spatial distribution of the rock permeabilities, and by the boundary conditions, as defined by the locations of the recharge and discharge areas. The aim of this study is to show schematically the deep groundwater flow patterns between the massives of the Aar and the Black Forest. The hydrogeological profiles illustrate three-dimensional flow fields inside a large volume of terrain and represent but one of the numerous solutions of the mathematical modelling realized. Computations have been performed for a steady state flow regime, which means that the boundary conditions do not vary with time.
On the basis of modelling results, it was possible to illustrate schematically the deep flow systems of the most important aquifers between the Aar massives and the Black Forest (Malm, Muschelkalk and upper Cristallin). An approximate but plausible representation of the groundwater circulation in deep aquifers was obtained thanks to the model. We are able to distinguish between the hydraulic relationships of two superimposed aquifers in various regions. The three-dimensional representation shows the outcrop zones of the different geological formations as well as the situation of recharge areas, which are characterised by high potentials, and discharge zones, which are characterised by low potentials in valleys represented by the hydrographic network.
Modelling results are then compared to available measurements in an attempt to validate the results. It is interesting to notice that it was possible, to a certain extent, to verify the modelling results by deep drillings. Most particularly, measurements of the hydraulic potentials at various depths in these boreholes have revealed upwellings close to the regional discharge areas.
Coupes géologiques et hydrogéologiques. 2ème partie: hydrogéologie: Représentation schématique des écoulements souterrains en Suisse
TracES/View - Traçage des Eaux Souterraines : Application SIG en milieu karstique jurassien (Suisse)
L'usage de traceurs artificiels est une méthode spécialement bien établie pour étudier les aquifères karstiques. Dans ce contexte, les traçages (avec des traceurs artificiels et biologiques) permettent de déterminer les limites des bassins versants, d'identifier la relation entre une perte et une résurgence, d'évaluer les phénomènes de diffluence, de déterminer le temps de transit, etc. Plus récemment les méthodes de traçage sont utilisées dans les études quantitatives de transport de polluant. Les essais de traçage prenant du temps et étant coûteux, une application (TracES/View) combinant les Systèmes d'Informations Géographiques (SIG) ArcInfo et ArcView, les deux couplés avec une base de données MS Access a été développée afin de planifier de façon efficace la réalisation de nouveaux essais de traçage. Une application utilisant ArcView, développée avec le language de programmation orienté-objets Avenue permet à des non-spécialistes en SIG d'accéder facilement aux éléments de la base de données des essais de traçage d'une manière graphique intuitive et interactive à l'écran. Utilisée conjointement avec d'autres cartes thématiques (la topographie, les surfaces structurales des formations géologiques, la délimitation des aquifères, les perméabilités, l'utilisation du sol, etc.), elle peut fournir un outil puissant d'aide à la décision pour la gestion des ressources en eaux souterraines., The use of artificial tracers is a specially well-established method to investigate karstic aquifers. In this case, tracing (artificial and biological tracers) enables to delimit watercatchment boundaries, to identify relation between a sinkhole and an outlet, to assess diffluent phenomena, transit time, etc. More recently tracer methods have been used in pollution transport studies. Tracer studies being time-consuming and expensive, an application (TracES/View) combining ArcInfo and ArcView Geographical Information Systems (GIS), both coupled with MSAccess database has been developped to provide an efficient way to plan the implementation and the planning of new tracer tests. An ArcView application developped with Avenue object-oriented scripting language allows GIS non-specialists to easily access data from tracer tests database in an interactive and intuitive way. Used in conjunction with other thematic maps (hydraulic conductivity, landuse, groundwater resources, and so on), it can provide a powerful decision-support tool for groundwater resources management.