Approche des transferts de pollution bactérienne dans une crue karstique par l'étude des paramètres physico-chimiques

L'exploitation des systèmes aquifères karstiques est toujours effectuée sous des contraintes liées à leur forte vulnérabilité. Une étude complète d'un épisode de crue de la source du Lez a été réalisée grâce à une coopération entre les Services de Santé et l'Université. Cette étude comporte une observation des paramètres physico-chimiques et bactériologiques sur une période de 15 jours, correspondant à une réponse hydrodynamique impulsionnelle sur la totalité du bassin. Les pas de temps d'échantillonnage varient de 4 à 24 heures.L'interprétation des résultats physico-chimiques met en évidence une disjonction nette entre les variations piézométriques et le passage de différents volumes d'eau. L'écoulement des eaux plus chaudes (16,5 °C) observé lors de l'étiage, eaux d'origine profonde plus chargées chimiquement se poursuit jusque vers le milieu de la décrue pour faire place à l'arrivée d'eaux plus froides correspondant à des infiltrations rapides puis retardées. Les eaux les plus chaudes sont caractérisées par des variations des teneurs en magnésium, les teneurs en calcium restant à peu prés constantes. Inversement; les eaux froides de l'infiltration retardée ont de faibles variations des teneurs en magnésium et sont tracées par une forte augmentation des valeurs en calcium.Le risque sanitaire maximal est lié au début de l'arrivée des eaux froides. Les eaux d'étiage et les eaux profondes sont légèrement contaminées. Les eaux d'infiltration retardée sont peu contaminées. En dehors des zones de perte du réseau hydrographique et des axes d'infiltration rapide, la vulnérabilité de l'aquifère est faible à l'échelle du bassin.The exploitation of karstic aquifer systems for the supply of potable water raises the problem of the evaluation of sanitary risks, in view of their great vulnerability. To supply a great urban tenter, a yield as high as several cubic metres per hour is required, and this magnitude corresponds to that of an underground basin of several km2, so that it is difficult to monitor and protect.Analytical observations from sanitary control platforms on potable water catchments have shown the existence of periods of high bacteriological pollution synchronizing systematically with periods of a rise of water.These bacteriological pollution transfers depend on the general conditions in which the aquifer functions. It seemed interesting, for the prevention of contamination, to examine all these hydrogeologic functions observed during a water rise, using bacteriological parameters.This study was based on observations made during an overall flood period following a prolonged drought throughout the whole basin supplying the city of Montpellier (France). The aim was to carry out a correlation test on the functioning of a karstic aquifer, with regard to :- the variation of the main physico-chemical parameters,- the principal pathogenic germs,- the commonly observed indicators of faecal contamination.This operation, undertaken in close collaboration with the sanitation board and the university authorities, required considerable investment in human, materiat and financial resources.Montpellier, a city with a population of 250 000 inhabitants, is supplied with potable water from the source of the River Lez. The water catchment is-situated upstream of a. major resurgence (12 m3/s during the water rise), tapping water from a principal drainage channel at a depth of 40 metres.The area of the basin feeding the spring was evaluated to be 150 km2 by adjustment to the 450 km2 of Jurassic and Cretaceous outcropping certified limestone, north of Montpellier. Even if the limits of the basin are not precisely defined, some of its parameters are well known. The aquifer consists of different structural zones, almost like independent sub-systems, having in common a rapid drainage network. The response observed at the exurgence is compared globally with the pluviometric signs, as well as with the effects produced in each structural zone, the transfer time, chemistry, temperature, recession, etc.The whole aquifer must be considered under pressure and it is this state of pressure which is probably responsible for the directional flow of the water from the rock matrix and of that circulating in the major karstification areas. The aquifer may be either in a state of injection or drainage and this notion is supported by the chemical and thermal fluctuations at the exurgence point.A one-year experimental programme, based on our knowledge of this aquifer, has been set up in collaboration with forecasters at the National Meteorological Office. All have been on the alert and ready to intervene, equipped with all the necessary staff and apparatus to ensure reliable sampling and analyses. The following procedures were performed :- sampling every 4 hours during the first 48 hours ;- sampling every 12 hours during the following 48 hours.Then until the end of the study, sampling took place every 24 hours with :- 1 bacteriological sample in sterile condition,- 1 sample for physico-chemical analyses in the laboratory,- temperature measurements with a 1/10° mercury thermometer,- resistivity measurements,- pH measurements with two standards,- a limigraphic reading.This period of water rise, hydrologically homogeneous throughout the whote basin in the form of a single impulsive response tasting about 10 days, was characterised by the circulation of two types of water masses : from the rock matrix and resutting from rapid infiltration. The mixture of these two bodies, each with a distinct chemical character, is a function of the state of pressure in the aquifer. At the end of the rise, a third type of water intervenes, that of retarded infiltration.The best criteria for identifying these volumes of water are thermal ones. The most variable elements are magnesium and calcium. Deep waters with a temperature of 16 °5 are characterised by a variation in magnesium, and cold water, by a variation in calcium. The highest value of calcium is related to the passage of water bodies attributed to the influence of retarded infiltration.The geological observations and the processing of results by factorial analyses show a clear distinction between the chemical rise and the piezometric rise. The hydraulic rise point is constituted by water with the saure chemical characteristics as that of the lowest water level. The most important dilution due to rapid transfer in the basin is observed in the middle of the water fait. These synchronized with the highest batteriological pollution rate for most of the elements.This study has provided a global appreciation of the sanitary risks and shows how pollution mechanisms function. Risks are permanent, even during the passage of the deepest water with a long residence time. This phenomenon raises the question of the duration and mode of survive of non encystable bacteria indicators in the karst system. The survival time appeared to be about a year or more.There is always a covariation between the physico-chemical elements and bacteriological pollution where the aquifer is under high pressure and when the water rises or has reached its maximum level, or when the water starts to fall. It is when the level of the water starts to drop that the main peaks of bacteriological pollution are observed. From this moment onwards, the whole basin functions like a drained system and the absence of covariation in the physico-chemical and bacteriological parameters are signs that the flow has become heterogeneous.For sanitation purposes it may be sufficient to monitor temperature and other chemical elements, in order to determine when an additional treatment of the water is required to maintain its potability. An appropriate apparatus is being devised to this end

Coupling the actuator line method to the high order meteorological les model Meso-NH to study wind farm wakes impacts on local meteorology

Offshore wind energy is now reaching the technological maturity, its capacity is increasing all over the world and this trend is projected to continue for several more years. Given this expectation, a better understanding of the relationship between the presence of wind farms and the atmospheric boundary layer is needed. Turbulent wakes produced by wind turbines can significantly impact the flow dynamics within wind farms and downstream of them. Operating offshore parks have already shown losses on energy production and effects on the local climate. In order to analyse the interactions occurring during these impacts, a new tool has been developed. This numerical tool is a coupling between the Actuator Line Method (ALM) and the open-source, non-hydrostatic mesoscale atmospheric model Meso-NH, based on the Large Eddy Simulation (LES) framework. The coupled Meso-NH + ALM system is first validated by using the experimental data obtained during the New MEXICO experiments. In particular, simulated and experimental loadings along the blades are compared. Then, a simulation of an idealized Horns Rev wind farm is performed using met mast measurements and reanalysis data for the “Horns Rev 1 photo case” as initial conditions. This new coupled system allows the exploration of the impact of wind farms on the lower levels of the atmosphere.Fil: Joulin, P. A.. French Institute of Petroleum Énergies nouvelles; Francia. Centre National de Recherches Météorologiques; FranciaFil: Mayol, María Laura. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Centro de Simulación Computacional para Aplicaciones Tecnológicas; ArgentinaFil: Blondel, F.. French Institute of Petroleum Énergies nouvelles; FranciaFil: Masson, Viviana Patricia. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Centre National de Recherches Météorologiques; FranciaFil: Rodier, Q.. Centre National de Recherches Météorologiques; FranciaFil: Lac, C.. Centre National de Recherches Météorologiques; Franci

A laser triggered electron source for pulsed radiolysis

We present the design of a photo-injector based accelerator for pulsed radiolysis applications. This machine is destined to meet the needs of the physical chemistry community at the Universite de Paris XI. A 4 MeV Energy electron pulse of a few picoseconds duration and with a charge in the range of 1 to 10 nC is produced from a Cs/sub 2 /Te photocathode. The photocathode is placed in the half energy spread cell of a 1-1/2 cell, 3 GHz RF gun, whose design is based on the gun used for the drive beam of the CERN CLIC Test facility. A 4 cell "booster" cavity is then used to accelerate the beam to an energy of 9 MeV. The transport system consists of a quadrupole triplet downsteam of the booster, two rectangular, 30 degree bend, dipoles with a pair of quadrupoles between them and a second triplet downstream of the second dipole. Energy dependent path length effects in the two dipoles allow the possibility of magnetic bunch compression depending on the phase-energy correlation of the bunch exiting the booster cavity. The beam envelope and the bunch length have been calculated through the transport line using TRACE-3d and PARMELA. These codes allow us to verify the required beam parameters at the experimental areas. We discuss the adjustment of the optics, aimed at producing the minimum electron bunch length at the experimental targets. (4 refs)

Swelling of Transported Smoke from Savanna Fires over the Southeast Atlantic Ocean

We use the recently released Cloud Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) Version 4.1 (V4) lidar data to study the smoke plumes transported from Southern African biomass burning areas. Significant improvements in the CALIPSO V4 Level 1 calibration and V4 Level 2 algorithms lead to a better representation of their optical properties, with the aerosol subtype improvements being particularly relevant to smoke over this area. For the first time, we show evidence of smoke particles increasing in size, evidenced in their particulate color ratios, as they are transported over the South Atlantic Ocean from the source regions over Southern Africa. We hypothesize that this is due to hygroscopic swelling of the smoke particles and is reflected in the higher relative humidity in the middle troposphere for profiles with smoke. This finding may have implications for radiative forcing estimates over this area and is also relevant to the ORACLES field mission

Swelling of Transported Smoke from Savanna fires over the Southeast Atlantic Ocean

We use the recently released Version 4 (V4) lidar data products from CALIPSO to study the smoke plumes transported from Southern African biomass burning areas. The significant improvements in CALIPSO V4 Level 1 calibration and the V4 Level 2 aerosol subtyping algorithms, the latter being particularly relevant to biomass burning smoke over this area, lead to a better representation of their optical properties. For the first time, we show evidence of smoke particles increasing in size, evidenced in their particulate color ratios, as they are transported over the South Atlantic Ocean from the source regions over Southern Africa. This is likely due to hygroscopic swelling of the smoke particles and is reflected in the higher relative humidity in the middle troposphere for profiles with smoke. This finding may have implications for radiative forcing estimates over this area and is relevant to the ORACLES field mission that is currently underway

Surface plasmons of metallic surfaces perforated by nanoholes

Recent works dealt with the optical transmission on arrays of subwavelength holes perforated in a thick metallic film. We have performed simulations which quantitatively agree with experimental results and which unambiguously evidence that the extraordinary transmission is due to the excitation of a surface-plasmon-polariton (SPP) mode on the metallic film interfaces. We identify this SPP mode and show that its near-field possesses a hybrid character, gathering collective and localised effects which are both essential for the transmission.Comment: 16 pages, 4 figure

On unitarizability in the case of classical p-adic groups

In the introduction of this paper we discuss a possible approach to the unitarizability problem for classical p-adic groups. In this paper we give some very limited support that such approach is not without chance. In a forthcoming paper we shall give additional evidence in generalized cuspidal rank (up to) three.Comment: This paper is a merged and revised version of ealier preprints arXiv:1701.07658 and arXiv:1701.07662. The paper is going to appear in the Proceedings of the Simons Symposium on Geometric Aspects of the Trace Formul

Aquaporin-4 and brain edema.

Aquaporin-4 (AQP4) is a water-channel protein expressed strongly in the brain, predominantly in astrocyte foot processes at the borders between the brain parenchyma and major fluid compartments, including cerebrospinal fluid (CSF) and blood. This distribution suggests that AQP4 controls water fluxes into and out of the brain parenchyma. Experiments using AQP4-null mice provide strong evidence for AQP4 involvement in cerebral water balance. AQP4-null mice are protected from cellular (cytotoxic) brain edema produced by water intoxication, brain ischemia, or meningitis. However, AQP4 deletion aggravates vasogenic (fluid leak) brain edema produced by tumor, cortical freeze, intraparenchymal fluid infusion, or brain abscess. In cytotoxic edema, AQP4 deletion slows the rate of water entry into brain, whereas in vasogenic edema, AQP4 deletion reduces the rate of water outflow from brain parenchyma. AQP4 deletion also worsens obstructive hydrocephalus. Recently, AQP4 was also found to play a major role in processes unrelated to brain edema, including astrocyte migration and neuronal excitability. These findings suggest that modulation of AQP4 expression or function may be beneficial in several cerebral disorders, including hyponatremic brain edema, hydrocephalus, stroke, tumor, infection, epilepsy, and traumatic brain injury