Mélange des eaux de la nappe phréatique et de la rivière

Mélange des eaux de la nappe phréatique et de la rivièr

La détermination de l'âge au sevrage nutritionnel des singes colobes Magistrat du Ghana grâce aux isotopes fécaux stables des mères et des nourrissons : une contribution à la primatologie comparative

L'âge au sevrage est un trait d'histoire de vie qui affecte le succès reproductif des femelles. Sa détermination à partir d'observations de la tétée est limitée en raison de l'allaitement de confort ou de nuit. Le suivi de l'alimentation des nourrissons, à partir des isotopes stables de carbone et d'azote fécaux (δ13C, δ15N %N) est une alternative précise et non invasive aux méthodes comportementales. Les âges de sevrage chez le colobe magistrat (Colobus vellerosus) à BFMS, Ghana, ont été déterminés en utilisant les δ13C et δ15N fécaux, et ceux-ci ont été comparés aux évaluations comportementales du sevrage. Les différences d'âge au sevrage entre trois groupes de colobes différents ont également été comparées. Des échantillons fécaux ont été collectés auprès de 8 dyades de mères (N = 88 fèces) et de leurs enfants (N = 98 fèces). Les échantillons ont été homogénéisés et analysés dans un spectromètre de masse à rapport isotopique et un analyseur élémentaire. L'âge moyen du sevrage chez tous les nourrissons ayant utilisé des isotopes stables fécaux était de 15,75 mois, ce qui était supérieur à l'âge moyen du sevrage déterminé à partir des observations de l'allaitement (14,6 mois). Deux nourrissons ont été sevrés avant le début de la collecte des données fécales, deux avaient un âge isotopique au sevrage similaire à leur âge de sevrage comportemental, et deux avaient un âge isotopique au sevrage supérieur à leur âge comportemental. Deux nourrissons dont on a déterminé qu'ils n'étaient pas encore sevrés d'après les évaluations isotopiques n'ont pas été observés en train de téter et ont montré des différences δ15N nourrisson-mère alternativement plus grandes et plus petites entre 6 et 9 mois. Cela peut indiquer un processus de sevrage cyclique, les nourrissons devenant plus ou moins dépendants du lait au cours de la période de 4 mois. Il semblait y avoir des différences dans les âges moyens de sevrage isotopique entre les groupes. Mon étude a montré que les isotopes stables fécaux peuvent être utilisés avec succès pour surveiller le développement nutritionnel des nourrissons et les différences de niveau trophique entre le nourrisson et la mère chez les singes colobes arboricoles.Age at weaning is a life-history trait that affects the reproductive success of females. Its determination from observations of suckling is limited due to comfort and night nursing. To monitor infant diets, fecal stable carbon, and nitrogen isotopes (δ13C, δ15N %N) provide an accurate and non-invasive alternative to behavioral methods. Weaning ages in ursine colobus (Colobus vellerosus) at BFMS, Ghana was determined using fecal δ13C and δ15N, and these were compared to behavioral weaning assessments. I also compared differences in weaning ages between three different colobus groups. Fecal samples were collected from 8 dyads of mothers (N = 88 feces) and their infants (N = 98 feces). The samples were homogenized and analyzed in an isotope ratio mass spectrometer and elemental analyzer. The mean weaning age among all infants using fecal stable isotopes was 15.75 months, which was older than the mean weaning age determined from observations of nursing (14.6 months). Two infants were weaned before fecal data collection began, two had an isotopic age at weaning similar to their behavioral weaning age, and two had an isotopic age at weaning that was older than their behavioral age. Two infants who were determined to be not yet weaned from isotopic assessments were not observed to nurse and showed alternately larger and smaller δ15N infant-mother differences between 6 and 9 months. This may indicate a cyclic weaning process, with infants becoming more or less dependent on milk over the 4-month period. There appeared to be differences in the average isotopic weaning ages between groups. My study showed that fecal stable isotopes can be successfully used to monitor infant nutritional development and infant-mother trophic level differences in arboreal colobus monkeys

Les expériences de Ruben et Kamen (1941) à travers les manuels scolaires

Les expériences de Ruben et Kamen sont évoquées dans la plupart des manuels de biologie des classes de Première et de Terminale. À partir d'une étude de la présentation et de l'exploitation de celles-ci à des ßns didactiques, nous soulevons les erreurs de contenu et de raisonnement avant de discuter à travers cet exemple d'une meilleure utilisation de l'histoire des sciences dans l'enseignement de la biologie

Développement de méthodes de calcul de coefficients de sensibilité des sections efficaces multigroupes autoprotégées et de sensibilité implicite du Keff aux densités isotopiques

Les codes de calculs déterministes utilisant un schéma de calcul multigroupe, il est nécessaire de procéder à des calculs d’autoprotection des résonances avant de procéder aux calculs de transport neutronique. Ces calculs donnent des sections efficaces multigroupes pour lesquelles les dépressions dans le flux aux énergies des résonances ont été adéquatement prises en compte. Pour chaque système pour lequel on veut faite un calcul de transport, on doit faire un calcul d’autoprotection préalable. Les sections efficaces multigroupes, pour les réactions résonantes, dépendent donc du système à analyser. Cela implique donc qu’une variation sur un paramètre du système, par exemple sur une densité isotopique, a un impact sur les sections multigroupes résonantes. Il devient alors pertinent de distinguer entre deux types d’effets résultant d’une variation d’un tel paramètre. Le paramètre en question peut apparaître explicitement dans l’équation de transport (par exemple, une densité entre dans cette équation à travers la section macroscopique du mélange correspondant) et ainsi causer une perturbation sur le keff (ou toute autre quantité obtenue en résolvant l’équation de transport). Il s’agit alors d’un effet explicite. Mais cette variation d’un paramètre peut aussi affecter les calculs d’autoprotection et perturber les sections efficaces résonantes multigroupes, qui à leur tour peuvent causer une perturbation sur le keff. C’est ce qu’on appelle un effet implicite. Ces effets implicites vont en général, pour diverses raisons, dans le sens contraire des effets explicites, c’est-à-dire qu’ils contribuent à une variation sur le keff ayant le signe opposé à celui de la contribution explicite. Quand une variation sur un paramètre entraîne une perturbation sur un autre paramètre, suite à un calcul de transport par exemple, on peut établir des coefficients de sensibilité entre les deux paramètres. Dans cette thèse, il sera question des sensibilités des sections efficaces autoprotégées et du keff aux différentes densités isotopiques. Plus précisément, on développe ici des méthodes permettant de calculer les coefficients de sensibilité des sections autoprotégées pour deux modèles d’autoprotection, un par dilution équivalente et un par sous-groupes. Une fois ces coefficients obtenus, on peut les combiner avec les coefficients de sensibilité du keff aux sections efficaces multigroupes pour obtenir des coefficients de sensibilité implicite du keff . Les méthodes de calcul de sensibilité de sections efficaces développées ici se basent sur un calcul des dérivées des probabilités de collision.----------Abstract Since deterministic codes use a multigroup scheme, self-shielding calculations are required before one can carry out neutron transport calculations. These calculations are used to obtain multigroup cross sections where flux depressions at resonance energies are properly taken into account. For each system where a transport solution is required, self-shielding calculations must be carried out beforehand. Multigroup cross sections in the resonant energy range are therefore system-dependent quantities. This means that a variation on a reactor parameter, an isotopic density for example, will have an impact on the resonant self-shielded cross sections. It is therefore relevant to distinguish between two types of effects resulting from a variation on a given parameter. This parameter can explicitly appear in the transport equation (for example, an isotopic density explicitly appears through the macroscopic cross sections of the corresponding mixture) and perturb the multiplication factor keff (or any other quantity obtained from solving the transport equation). This is called an explicit effect. This parameter variation can also affect self-shielding calculations and perturb resonant multigroup cross sections, which can themselves cause a variation of keff . This is what we refer to as an implicit effect. In general, the keff perturbations resulting from the implicit effect have the opposite sign of those resulting from the explicit effect. When a variation on a parameter leads to a perturbation on another parameter, following a transport calculation for instance, we can compute sensitivity coefficients between those two parameters. In this thesis, we consider the self-shielded cross sections and keff sensitivity coefficients to isotopic densities. More precisely, we develop methods to compute the selfshielded cross sections sensitivity to densities arising from two different self-shielding models, an equivalent dilution model and a subgroup model. Once these coefficients are known, they can be combined with the keff sensitivity coefficients to the multigroup cross sections to obtain the keff implicit sensitivity coefficients to the isotopic densities. The self-shielded cross sections sensitivity computation methods developed here are based on the computation of the derivatives of the collision probabilities. Both self-shielding models considered here are based on the computation of the collision probabilities. These probabilities are then used to solve the slowing-down equation for the flux to be used for the evaluation of the self-shielded cross sections. For both self-shielding models, we develop a sensitivity analysis method by analytically differentiating all the relevant equations and then solve for the derivatives of the self-shielded cross sections with respect to the isotopic densities

Use of stable isotope signatures (δ13C & δ15N) in the Black Sea Danubian area – new approach for understanding the influence of terrestrial discharge upon the marine ecosystem

Abstract. Coastal marine zones located in front of large rivers are of major biological interest. In these areas, the origin of the organic matter is complex and highly variable. The continental inputs, added to the nutrients already present in the marine environment, influence considerably the productivity and functioning of the ecosystems. Used for the first time in aquatic ecology on the Romanian coast, the proportion of stable isotopes of carbon (13C/12C) and nitrogen (15N/14N) allowed the identification of the organic material sources (terrestrial and marine) as well as the analysis of the food webs due to the predictable isotopic relation between consumers and their food. Preliminary analyses of stable isotopes of the particulate organic matter POM of the Danube water as well as marine POM, sediments and marine organisms were made on 186 samples collected at 10 stations in October 2004. The identification of the isotopic signatures of the main sources of organic material (terrestrial and marine) was achieved along with those of some groups of marine organisms present in this area (macrophytes, bivalves, polychaetes, amphipods, macrurans, brachyurans and fish). The results obtained in the Black Sea were compared with those of the Mediterranean Sea seawards the Rhone river and showed that the isotopic signatures of the two river POM were close to each other, whereas they largely differed in marine phytoplankton and macrophytes

Vulnérabilité de l’eau souterraine à la contamination par les nitrates sur le bassin versant de la rivière Noire (Montérégie, Québec)

La rivière Yamaska est l’un des affluents du Saint-Laurent les plus contaminés par les activités agricoles. Cette problématique touche particulièrement le sous-bassin de la rivière Noire où les dépôts de surface du Quaternaire sont discontinus, de faible épaisseur et souvent perméables. L’objectif de cette étude est de déterminer la vulnérabilité de l’eau souterraine sur une partie du sous-bassin de la rivière Noire (100 km2). La méthodologie utilisée comprend la caractérisation de l’aquifère, l’analyse des concentrations en nitrates et des contenus en δ18O, l’étude de la vulnérabilité en utilisant l’approche AQUIPRO et la modélisation hydrogéologique. Les résultats montrent une dégradation significative et d’origine anthropique de l’eau souterraine : plusieurs concentrations excèdent 1 mg N-NO3/L et quelques-unes excèdent 10 mg N-NO3/L. Les puits contaminés sont situés sur les crêtes topographiques où le silt argileux est absent et le till discontinu, et où la plus grande vulnérabilité AQUIPRO a été identifiée. Une diminution des concentrations avec la profondeur de prélèvement s’explique par un écoulement souterrain peu profond entraînant les nitrates vers un ruisseau et vers la rivière Noire. La vulnérabilité de l’eau souterraine est ainsi beaucoup plus grande dans les couches superficielles du roc fracturé. Le temps moyen de séjour de l’eau souterraine est estimé à 20 ans. Les concentrations mesurées permettent d’établir un lien direct entre la vulnérabilité, les dépôts de surface, la stratigraphie du substrat et les directions de l’écoulement souterrain. Elles démontrent aussi la présence d’une contamination de l’eau souterraine par les nitrates qui est susceptible d’augmenter si aucune mesure préventive n’est mise en place.Many studies have shown a link between intensive agricultural practices and groundwater pollution by nitrates. In Québec, recent studies have shown that the Yamaska River is highly contaminated by agricultural activities. Maize and pork production are particularly intensive in the Noire River sub-basin. In this area, quaternary deposits are discontinuous, of limited thickness and are generally permeable, leading to high groundwater vulnerability. The objective of this study was to determine groundwater vulnerability to nitrate contamination on a small agricultural sub-watershed of the Noire River. The methodology included aquifer characterization, analysis of nitrate concentrations and δ18O composition, as well as a vulnerability evaluation and groundwater flow modelling.Located on the south shore of the Saint Lawrence River, the Noire River (1579 km2) is located in the southeastern portion of the Yamaska basin. A small part of the basin (100 km2) was the focus of this study. The Noire River flows in the centre of the study area whereas the Aulnages creek is a small tributary to the Noire River. The study area was limited to the east and west by topographic highs. It is located between the limit of the St. Lawrence Lowlands and the first Appalachian ridges. The bedrock, Cambrian to Ordovician in age, is mainly made of limestone in the western zone and is composed of terrigenous siliciclastic facies in the eastern zone. The substratum forms elongated crests, due to the tectonic grain, surrounded by recent surface deposits. These quaternary deposits are discontinuous and are of limited thickness. The hydrological potential of the fractured rock aquifer is interesting but spatially variable.The deposits were analyzed at 50 observation sites and 18 typical samples were sieved or submitted for density analysis (GEOTERAP). Data from the Système d’Information Hydrogéologique (SIH) were used to complete the field information in establishing the stratigraphy of the area. Soil hydraulic conductivity was measured using a Guelph permeameter and two short-term pumping tests were performed. Monthly water levels were measured in 18 private wells from June 2001 to June 2002. Water was sampled bimonthly from 35 sites (25 deep wells, two shallow wells, two sites in the Noire River, four in the Aulnages stream, and two in a temporary lake, located in a gravel pit). In October 2001 and April 2002, water was sampled for δ18O composition. Analyses were performed at the GÉOTOP-UQÀM-McGill laboratories. Aquifer vulnerability was determined using the AQUIPRO approach, a simple method that considers clay and till thickness, in addition to well depth. A groundwater flow model was developed using MODFLOW and MODPATH to simulate groundwater flow, flow paths and residence times.Characterization of the quaternary deposits confirmed the following sequence, from the base to the top: till; clayey silts; sand and sandy gravel. The thickness of these deposits was variable, and there were bedrock outcrops, mainly on the western and eastern sides of the study area. A north-south esker (partially exploited) is present on the western side of the Noire River. Measured soil hydraulic conductivities show that the clayey silts and till deposits have low permeability whereas the sand is more permeable. Clayey silts present in the centre of the study area, as well as occasional till deposits, offer partial protection to the aquifer, whereas elsewhere infiltration and contaminants can reach the aquifer through recharge. Pumping tests showed high transmissivities for the rock formation, probably resulting from the important rock fracturing in the upper 10 to 15 m of the aquifer. Groundwater flowed towards the river from the eastern and western limits of the study area, and water depth was on average 2.5 m. The Noire River is generally in contact with rock and drains the aquifer.Measured nitrate concentrations exceeded 10 mg  N‑NO3/L (guideline for potable water) in the two sampled surface wells. Concentrations were between 1 and 10 mg N-NO3/L at least once during the study period in ten of the 25 deep sampled wells, indicating a groundwater contamination problem of anthropogenic origin. The highest concentrations were measured in recharge areas and nitrate concentrations were found to decrease generally with well depth. Nitrate concentrations were higher in the Aulnages creek than in the Noire River, probably because the creek intercepts drainage water and shallow groundwater flow. The isotopic composition of surface wells, deep wells and Aulnages creek water remained relatively stable between sampling times. This indicates an important mixing of fresh recharge with in situ groundwater. In the Noire River, δ18O compositions reflect the yearly variations in precipitation.AQUIPRO aquifer vulnerability was highest in the eastern and western parts of the study area where the highest nitrate concentrations were measured. AQUIPRO vulnerability was lowest where the clayey silts provide some protection near the Noire River. The results showed an important spatial heterogeneity in the thickness of the clayey silt layer, underlining the generally high aquifer vulnerability in the study region. The groundwater flow model developed using field data simulated the measured heads adequately. Flow directions simulated with MODPATH confirmed the presence of a shallow groundwater flow from the eastern and western limits and towards the Noire River. This flow is probably responsible for the decreasing nitrate concentrations observed with increasing water sampling depth and confirms that aquifer vulnerability varies with depth in the aquifer. The average groundwater residence time is 20 years. This means that recharge will take on average 20 years to travel through the aquifer and to the Noire River. It also indicates the time frame required for the aquifer to eliminate a large-scale nitrate contamination, after the initiation of control measures.This work showed that groundwater nitrate contamination is related to groundwater vulnerability, which is a function of quaternary deposits, substrate stratigraphy and groundwater flow directions. These factors must be considered when studying groundwater vulnerability as they directly affect contaminant transport. It therefore appears necessary to use a combination of various approaches to better understand aquifer vulnerability and to design preventive measures. This work also demonstrated groundwater contamination by nitrates in the study region. Because of the generally high vulnerability of the aquifer, increased nitrate contamination can be expected in the future if no preventive measures are undertaken to protect the groundwater resource