Délimitation des périmètres de protection des puits de pompage en zone agricole à l'aide de la simulation mathématique

Un périmètre de protection de puits de pompage est la surface entourant le puits, dans laquelle des mesures sont prises pour empêcher des contaminants de migrer et de contaminer l'eau de ce puits. Dans l'établissement des périmètres de protection, de nombreux facteurs doivent être considérés, et une approche analytique systématique doit être adoptée. Les modèles mathématiques de simulation peuvent être employés en ce sens et sont souvent les seules méthodes capables de déterminer les périmètres de protection quand des critères quantitatifs sont utilisés. Une telle approche a été appliquée, en couplant un modèle de transport de contaminant en zone non saturée avec un modèle de transport en zone saturée. Le modèle en zone non saturée VULPEST évalue les concentrations de pesticide atteignant la nappe. Ces concentrations sont ensuite utilisées comme données d'entrée du modèle en zone saturée. Ce dernier considère les vitesses d'écoulement et l'influence de chaque puits. Les résultats quantitatifs permettent alors la détermination de périmètres de protection spécifiques à chaque contaminant potentiel. Cette application, réalisée sur un important site de culture de la pomme de terre du Québec, e permis de comparer favorablement les concentrations prédites à celles mesurées dans l'eau d'un puits, et de déterminer le périmètre de protection spécifique au pesticide utilisé. Le cas présenté est un exemple des applications possibles et futures d'une telle méthode pour la détermination des périmètres de protection des puits de pompage.A wellhead protection area is the surface and subsurface area surrounding a waterwell through which contaminants are reasonably likely to move toward and reach. In the past, various approaches have been taken to delineate wellhead protection areas : fixed circles or rings around the well; simplified variable shapes based on geo-hydrologic mapping and classification ; zones with prescribed minimum travel times. However, in establishing wellhead protection areas, many factors need to be considered : zone of influence around the well; well recharge area; flow paths; transport velocities; travel times; sources and types of contamination. To determine a site-specific wellhead protection area, a systematic analytic approach must be taken. Mathematical simulation models may be employed and are often the only method capable to determine the wellhead protection area when quantitative criteria are used.Such an approach can be used in agricultural zones, where pesticides are applied, by coupling a solute transport modal for the unsaturated zone with a saturated zone transport model. The (unsaturated zone) VULPEST model is an evaluation tool for the groundwater contamination by pesticides based on the transport modeling. Developed as a management tool, it permits the evaluation of the groundwater vulnerability to pesticides in terme of risk of contamination. It evaluates the concentrations of pesticide that reach the water table, taking into account the spatial variability of hydrodynamic, physical and physicochemical parameters of the soil. The variability of parameters is taken into account in the Monte Carlo approach. This approach consists of carrying out a sufficient number of simulations so that the distribution of values assigned to each parameter, these values being randomly selected from a chosen probability distribution, approximates the given distribution.The concentrations obtained from the VULPEST model are used as input data in the model which simulates the transport and the fate of the contaminant in the saturated zone. This model uses the finite difference technique to simulate flow and solute transport. It considers the flow velocities and the influence of each well. In steady state conditions, the linked transport models in unsaturated and saturated zones may be considered independent. The quantitative results obtained by these means determine the vulnerability level of the well. Finally, they permit the delineation of the wellhead protection area for a specific contaminant, that is a given pesticide.An application was performed to an important potato crop area in Quebec. Few years ago, this site has shown a contamination of the well water by the pesticide aldicarb. The cultivated soil consists of marine and fluvial sand with medium to coarse grain sizes, deposited on a sea clay with a thickness of about 20 m in some places. Potatoes are intensively grown in this region. In the eighties, a contamination by the pesticide aldicarb was noticed in some wells of this region. The granular form of aldicarb is applied during the sowing period (mid-May) at the recommended rate of 2.24 kg/ha. It has a high solubility (6 000 mg/l) and is leached by soil humidity. The aldicarb is transformed by oxidation to sulfoxide then to sulfone during its transit in the unsaturated zone. After a characterization of the soil physical parameters, calculations were run for both the unsaturated and the saturated zones. The depths of the well and the aquifer are 5 m and 3 m respectively. The thickness of the aquifer affected by pumping is about 2 m. The application of the pesticide aldicarb was done during 1982 and 1983.The predictive results obtained by modelling for the pesticide concentrations in the well water were favorably comparerd to the concentrations measured at the site. The concentrations of pesticide in the water reach their peaks 7 weeks after every application. The maximum concentrations reaching the water table were found to be about 0,5 mg/l. This level exceeds largely the water quality criterion of 9 µg/l set by Health and Welfare Canada, and the one of 10 µg/l of the US-EPA. The well concentrations are calculated by taking into account transport in the saturated zone and decay processes. The maximum concentrations obtained are near 24 µg/l for a decay rate of the pesticide in the aquifer of 0,003 d-1. This decay rate is the one corresponding of the hall-lite of 8 months found by other researchers for Florida soils. The analysis of the water well during this period shows concentrations of about 10 µg/l. Moreover, the leaching of the contaminant into the well, and its persistence in the soil and groundwater is still present over 3 years after the last application. Using the water quality criterion of 9 µg/l set by Health and Welfare Canada, calculations have provided the delineation of the wellhead protection area specific to the pesticide aldicarb. The boundary delineation of water well protection area is determined by the numerical technique of reverse path line. The maximum extension of the well protection area obtained by this mean is 110 meters. It corresponds to a peak arrival with a decay of 1.5 years after the application.The case study shows an example of the possible and future applications for such a method for the delineation of the wellhead protection areas. Such an approach permits to council the best use of pesticides with an appropriate groundwater protection scheme, indeed, agricultural managers can safely decide on the pesticide application rate and date, as on the choice between various pesticides, with regard to the groundwater quality protection. Through this way, regulators and scientists can base their decisions for the registration of new pesticides by testing, before their use, their possible impacts on groundwater. Comparisons can be easily doge between water quality criteria and predicted quantifies, and regulatory decisions can be taken in light of these results

Analyse de sensibilité paramétrique d'un modèle simulant le transport de pesticide dans le sol

Afin de protéger l'eau souterraine des pesticides épandus à la surface des sols agricoles, on doit être capable de prédire et d'évaluer a priori les risques de contamination. La modélisation mathématique, qui est basée sur la représentation des processus, s'avère être un outil à privilégier pour une telle prédiction. Cependant, la fiabilité des résultats de ces modèles est fonction de la précision et de la représentativité des différents paramètres d'entrée. A l'aide d'une analyse de sensibilité, il est possible d'évaluer l'impact de la variabilité de ces paramètres sur les résultats de la modélisation. Une étude de sensibilité menée avec le modèle Pesticide Rosit Zone Model (PRZM) a permis d'identifier les paramètres physiques d'entrée dont la variation apporte le plus de changements au niveau des principaux résultats, c'est-à-dire les paramètres d'entrée auxquels le modèle est le plus sensible. L'utilisation du coefficient de sensibilité relatif s'avère être à cet égard un outil de comparaison fort efficace dans le cadre d'une telle étude. Les paramètres d'apport en eau (précipitations) et en pesticide (taux d'application) sont ceux dont les variations provoquent le plus d'impact au niveau des résultais de la simulation. Egalement, les résultats des simulations sont aussi sensibles aux variations de la capacité au champ et de la densité du sol. La température, le point de flétrissement, ta profondeur d'évaporation et la dispersion sont des paramètres auxquels la modélisation est peu sensible.The ever increasing number of cases of groundwater contamination by pesticides has recently given rise to numerous experimental studies on the tale of these compounds within the soil-water system. In parallel with these experimental studies, the quick and intensive development of numerous simulation models bas emphasized the importance of the various factors and processes controlling the transport of pesticides in the unsaturated zone. The calibration and the validation of such deterministic models, which are especially used in groundwater management, requires the evaluation of several parameters related to the nature of the pesticide as well as to the pedologic and hydrogeological conditions of a given site. The reliability of results predicted by those models is mainly a function of the precision and the representativeness in the evaluation of those parameters at a specific site.The aim of this study was to evaluate the sensitivity of a simulation modes of pesticide movement in the unsaturated zone with regards to the variation in soil physical properties. More particularly, a sensitivity analysis was performed in order to determine the importance of the variation in these parameters with respect to simulation results obtained from the Pesticide Root Zone Model (PRZM). The spatial variability of the composition and structure of the soil, which comes from the site pedogenesis, is the main cause of the variability of the soil water distribution and of the soil transient properties. The sensitivity analysis of a model with respect to the variation in these parameters allows the evaluation of the impact of their representativeness on the model output results. Such an analysis thus allows the determination of an acceptable level of precision (or error) for which an increase of precision in the evaluation of a parameter does not anymore correspond to a significant gain in the representativeness of the model results. It also permits the estimation of the impact of a potential variation of a parameter on the prediction of pesticide transport in the unsaturated zone.The deterministic PRZM modal used in this study has been developed by the US-EPA and devoted to pesticide application on agricultural sites. This modal evaluates the pesticide leaching towards groundwater with respect to the type of culture and pesticide used, the climatic conditions, the soil characteristics and some agricultural practices. Output results from the model can he expressed in concentrations or masses of pesticide, in fluxes or cumulated quantities. Simulations were performed using characteristics and data of the Portneuf region (Quebec). This area of potato farming was until recently one of the Quebec most important sites for aldicarb application before the recommendation of its non use. Cultivated surfaces, which are rather homogeneous, consist of medium-size sand. Simulations were performed river a ten year period (1974 to 1984), implying one application of pesticide a1 the seed-time, and a trop for each year.The parameters of water and pesticide inputs (rain and application rates) are those that induce the higher impact on the simulation results. The simulation results were also influenced by the variation of the field capacity and of the soil bulk density. Temperature, wilting point, maximum evaporation depth and dispersion are the input parameters for which the PRZM model is the less sensitive. The simulation results of pesticide transport, which ultimately consist in predicting the groundwater contamination, are very sensitive to the variations of some physical parameters for which the precision and the representativeness in the measured values are thus very important for the reliability of the results. Considering the spatial variability of a site characteristics, the representativeness of these results is very uncertain if a limited number of data is used in order to determine the mean value. A particular attention has to be focused on the parameters that induce the higher sensitivity of the model. Finally, such a sensitivity analysis shows that a stochastic approach in modelling the solute transport through soil can be a good alternative to take into account the variability of parameters encountered in field situations

Bacterial Death Results from Mutations Made in Translocation Peptide of Leucyl-tRNA Synthetase

The family of aminoacyl-tRNA synthetases (aaRSs) ensures the fidelity of translation through providing a pool of correctly aminoacylated tRNA products that become incorporated by the ribosome. Leucyl-tRNA synthetase (LeuRS) has two functionally separate domains, one is the aminoacylation domain and the other is the CP1 editing domain. LeuRS can aminoacylate noncognate amino acids, therefore it relies on the CP1 editing domain to hydrolyze misaminoacylated tRNA products before they are released from the enzyme. The LeuRS enzyme must undergo a structural transition state in its reaction cycle in order to translocate the 3\u27 acceptor stem of tRNA 30 Å from the aminoacylation active site to the CP1 domain hydrolytic active site. The translocation event is difficult to study, but we believe that we have generated mutations within LeuRS that alter the translocation event of tRNA. The mutations that we have generated lead to bacterial death in Escherichia coli (E. coli). Circular dichorism experiments indicate that our mutations do not significantly alter the secondary structure of LeuRS. In vitro biochemical studies demonstrate that these mutations reduce the rates of aminoacylation and hydrolysis, while also displaying misaminoacylation activity. We attribute these biochemical findings to the resulting bacterial death that is caused by these mutation

Bacterial Death Results from Mutations Made in Translocation Peptide of Leucyl-tRNA Synthetase

The family of aminoacyl-tRNA synthetases (aaRSs) ensures the fidelity of translation through providing a pool of correctly aminoacylated tRNA products that become incorporated by the ribosome. Leucyl-tRNA synthetase (LeuRS) has two functionally separate domains, one is the aminoacylation domain and the other is the CP1 editing domain. LeuRS can aminoacylate noncognate amino acids, therefore it relies on the CP1 editing domain to hydrolyze misaminoacylated tRNA products before they are released from the enzyme. The LeuRS enzyme must undergo a structural transition state in its reaction cycle in order to translocate the 3\u27 acceptor stem of tRNA 30 Å from the aminoacylation active site to the CP1 domain hydrolytic active site. The translocation event is difficult to study, but we believe that we have generated mutations within LeuRS that alter the translocation event of tRNA. The mutations that we have generated lead to bacterial death in Escherichia coli (E. coli). Circular dichorism experiments indicate that our mutations do not significantly alter the secondary structure of LeuRS. In vitro biochemical studies demonstrate that these mutations reduce the rates of aminoacylation and hydrolysis, while also displaying misaminoacylation activity. We attribute these biochemical findings to the resulting bacterial death that is caused by these mutation

Increased prevalence of expiratory flow limitation during exercise in children with bronchopulmonary dysplasia.

Evidence regarding the prevalence of expiratory flow limitation (EFL) during exercise and the ventilatory response to exercise in children born preterm is limited. This study aimed to determine the prevalence of EFL as well as contributing factors to EFL and the ventilatory response to exercise in preterm children with and without bronchopulmonary dysplasia (BPD). Preterm children (=32 weeks gestational age) aged 9-12 years with (n=64) and without (n=42) BPD and term controls (n=43), performed an incremental treadmill exercise test with exercise tidal flow-volume loops. More preterm children with BPD (53%) had EFL compared with preterm children without BPD (26%) or term controls (28%) (p<0.05). The presence of EFL was independently associated with decreased forced expiratory volume in 1 s/forced vital capacity z-score and lower gestational age (p<0.05). There was no difference in peak oxygen uptake between preterm children with BPD and term controls (48.0 versus 48.4 mL·kg-1·min-1; p=0.063); however, children with BPD had a lower tidal volume at peak exercise (mean difference -27 mL·kg-1, 95% CI -49-?-5; p<0.05). Children born preterm without BPD had ventilatory responses to exercise similar to term controls. Expiratory flow limitation is more prevalent in children born preterm with BPD and is associated with airway obstruction and a lower gestational age

The Perception Of Walking Speed In A Virtual Environment

Studies of locomotion in virtual environments assume that correct geometric principles define the relationship between walking speed and environmental flow. However, we have observed that geometrically correct optic flow appears to be too slow during simulated locomotion on a treadmill. Experiment 1 documents the effect in a head-mounted display. Experiment 2 shows that the effect is eliminated when the gaze is directed downward or to the side, or when the walking speed is slow. Experiment 3 shows that the effect is unchanged by stride length. Experiment 4 verifies that the effect is not attributable to image jitter. The change in perceived speed from straight ahead to side or down gaze coincides with a shift from expanding optic flow to lamellar flow. Therefore, we hypothesize that lamellar flow is necessary for accurate speed perception, and that a limited field of view eliminates this cue during straight-ahead gaze

A framework for parameter estimation using sharp-interface seawater intrusion models

Funding : This work was supported by Quebec’s Ministère de l'Environnement et de la Lutte contre les changements climatiques (MELCC) [project « Acquisition de connaissances sur les eaux souterraines dans la région des Îles-de-la-Madeleine » (Groundwater characterization project in the Magdalen Islands region)]; and the Fonds québécois de la recherche sur la nature et les technologies (FRQNT) [International internship program accessed through CentrEau, the Quebec Water Research Center]. The authors would like to thank the Municipality of Les Îles-de-la-Madeleine for providing pumping datasets and information on current and historical groundwater management. They would also like to thank the team at Université Laval working on the Magdalen Islands project, for their help acquiring datasets and for field logistics, John Molson, for proofreading, and finally the two anonymous reviewers for their valuable comments. The authors would also like to thank Vincent Post for discussions on deep open boreholes, and Francesca Lotti and John Doherty for discussions on seawater intrusion modeling and data assimilation. J-C Comte and O Banton acknowledge the financial support from the Fonds d'Action Québécois pour le Développement Durable for the ERT data collection, undertaken as part of the Madelin'Eau consortium (Ageos-Enviro'Puits-Hydriad), and further thank the Municipality of Les Îles-de-la-Madeleine for fieldwork logistical and technical support.Peer reviewedproo

Expression profiling and cross-species RNA interference (RNAi) of desiccation-induced transcripts in the anhydrobiotic nematode Aphelenchus avenae.

BACKGROUND: Some organisms can survive extreme desiccation by entering a state of suspended animation known as anhydrobiosis. The free-living mycophagous nematode Aphelenchus avenae can be induced to enter anhydrobiosis by pre-exposure to moderate reductions in relative humidity (RH) prior to extreme desiccation. This preconditioning phase is thought to allow modification of the transcriptome by activation of genes required for desiccation tolerance. RESULTS: To identify such genes, a panel of expressed sequence tags (ESTs) enriched for sequences upregulated in A. avenae during preconditioning was created. A subset of 30 genes with significant matches in databases, together with a number of apparently novel sequences, were chosen for further study. Several of the recognisable genes are associated with water stress, encoding, for example, two new hydrophilic proteins related to the late embryogenesis abundant (LEA) protein family. Expression studies confirmed EST panel members to be upregulated by evaporative water loss, and the majority of genes was also induced by osmotic stress and cold, but rather fewer by heat. We attempted to use RNA interference (RNAi) to demonstrate the importance of this gene set for anhydrobiosis, but found A. avenae to be recalcitrant with the techniques used. Instead, therefore, we developed a cross-species RNAi procedure using A. avenae sequences in another anhydrobiotic nematode, Panagrolaimus superbus, which is amenable to gene silencing. Of 20 A. avenae ESTs screened, a significant reduction in survival of desiccation in treated P. superbus populations was observed with two sequences, one of which was novel, while the other encoded a glutathione peroxidase. To confirm a role for glutathione peroxidases in anhydrobiosis, RNAi with cognate sequences from P. superbus was performed and was also shown to reduce desiccation tolerance in this species. CONCLUSIONS: This study has identified and characterised the expression profiles of members of the anhydrobiotic gene set in A. avenae. It also demonstrates the potential of RNAi for the analysis of anhydrobiosis and provides the first genetic data to underline the importance of effective antioxidant systems in metazoan desiccation tolerance.RIGHTS : This article is licensed under the BioMed Central licence at http://www.biomedcentral.com/about/license which is similar to the 'Creative Commons Attribution Licence'. In brief you may : copy, distribute, and display the work; make derivative works; or make commercial use of the work - under the following conditions: the original author must be given credit; for any reuse or distribution, it must be made clear to others what the license terms of this work are

Highlights from the 6th International Society for Computational Biology Student Council Symposium at the 18th Annual International Conference on Intelligent Systems for Molecular Biology

This meeting report gives an overview of the keynote lectures and a selection of the student oral and poster presentations at the 6th International Society for Computational Biology Student Council Symposium that was held as a precursor event to the annual international conference on Intelligent Systems for Molecular Biology (ISMB). The symposium was held in Boston, MA, USA on July 9th, 2010

Police ethics and integrity: Can a new code overturn the blue code?

This paper analyses police officer perspectives on the seriousness of potential misconduct or unethical behaviour, and the factors that might shape whether they would report their colleagues' misdemeanours. It compares responses from police officers in UK three forces, looking at potentially corrupt behaviours described in a series of scenarios. The discussion includes why some types of misdemeanour seem more likely to be reported and the potential effects of a newly introduced formal Code of Ethics. In terms of differences between ranks and roles, and different responses from different services, the study suggests that the way police culture operates is significant and needs to be more widely addressed. The study used scenario based questionnaires to elicit views about the seriousness of certain police behaviours and to ask whether officers would report colleagues' misdemeanours. It develops a previous survey by one of the authors which conducted a similar survey published in 2005. Using the same questionnaire the new study examined a larger and more diverse sample of serving officers (n=520). This new study compares responses from police officers in UK three forces, geographically distributed across the country and have differing characteristics in terms of size, rurality, population density and policing priorities