Les tourbières abondent dans l’ensemble du Québec, mais celles de la vallée du Saint-Laurent subi... more Les tourbières abondent dans l’ensemble du Québec, mais celles de la vallée du Saint-Laurent subissent des pressions anthropiques majeures. Ces pressions et les pertes de superficies en tourbières qui en résultent sont à peu près inconnues. Nous avons mesuré la superficie occupée par les tourbières en 1966 et 2010 dans la région de Bécancour et identifié les perturbations récentes qu’elles ont subies à l’aide de la photo-interprétation et de validations sur le terrain. En 2010, les tourbières couvraient 17 500 ha, soit 6,1 % du territoire étudié. De cette superficie, 10 485 ha représentaient des tourbières encore intactes et 7 015 ha des tourbières ayant subi des perturbations limitées, notamment par la présence de canaux de drainage et de chemins forestiers. Entre 1966 et 2010, 5 433 ha de tourbières (près du quart des tourbières présentes en 1966) ont subi des perturbations irréversibles, principalement en raison de la culture de la canneberge (Vaccinium macrocarpon). Cette cultur...
Résumé Même si des travaux récents ont permis de caractériser certains aquifères du sud du Québec... more Résumé Même si des travaux récents ont permis de caractériser certains aquifères du sud du Québec, plusieurs demeurent encore très peu connus. Cette recherche a pour objectifs de comprendre la dynamique de l’écoulement souterrain et la vulnérabilité de l’aquifère du bassin de la rivière Noire (Montérégie, Québec), un bassin représentatif des aquifères de milieux fracturés situés en bordure des Basses-Terres du Saint-Laurent. Dans ce travail, un modèle de bilan hydrique en zone non saturée a permis de quantifier la distribution spatio-temporelle de l’infiltration sur le bassin. L’infiltration simulée moyenne est importante (215 mm•an‑1) et a lieu surtout au moment de la fonte printanière (74 %). L’infiltration la plus élevée se produit dans la partie amont du bassin, mais les résultats du modèle ne permettent pas d’évaluer quelle proportion de la recharge atteint effectivement l’aquifère régional profond. Sur l’ensemble du bassin, les concentrations en nitrate dans l’eau souterraine ...
Dans le cadre de la première et de la troisième phase du Programme d’acquisition de connaissances... more Dans le cadre de la première et de la troisième phase du Programme d’acquisition de connaissances sur les eaux souterraines (PACES) du MDDELCC, deux projets menés par l’Université du Québec à Montréal ont respectivement été lancés aux printemps 2009 et 2012, pour la zone Bécancour (2 924 km2) et la zone Nicolet / Bas-Saint-François (4 585 km2). Ces projets ont pour but d’établir les cartographies hydrogéologiques régionales et sont réalisés avec des partenaires locaux (CRÉ, MRC, municipalités, Agences de géomatique, OBV). Au total, 314 puits (municipaux, résidentiels ou nouvellement forés) ont été d’échantillonnés pour la chimie de l’eau, permettant de déceler 48 dépassements de norme de potabilité, soit pour le baryum (19), l’arsenic (14), le fluor (9), le plomb (2), l’antimoine (1) et l’uranium (1). Les dépassements d’objectifs esthétiques concernent principalement le manganèse (147), la dureté totale (75), le fer (66), et le pH (54). La plupart de ces dépassements seraient d’orig...
In areas where peatlands are abundant, they are likely to play a significant role in the hydrolog... more In areas where peatlands are abundant, they are likely to play a significant role in the hydrological and hydrogeological dynamics of a watershed. Although individual case studies are reported in the literature, there is a large range of aquifer–peatland interactions and there is a need to understand the controls of these interactions. The objectives of this study were (1) to better understand aquifer–peatland connections and how these may be predicted by geology and geomorphic location and (2) to provide a variety of reference sites for glacial geological settings. Slope and depression peatlands were studied in the Abitibi-Témiscamingue region and in the St. Lawrence Lowlands, two contrasting regions of southern Quebec. A total of 12 transects that span a shallow aquifer–peatland interface were instrumented with piezometers. Field investigations included peatland characterization, monthly water level monitoring, and continuous hydraulic head measurements with pressure transducers. ...
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Canadian Water Resources Journal / Revue canadienne des ressources hydriques
Understanding groundwater dynamics at the regional scale (> 100 km) is essential to the developme... more Understanding groundwater dynamics at the regional scale (> 100 km) is essential to the development of sustainable water management regulations. Groundwater flow models are increasingly used to support these strategies. However, in order to be reliable, these models need to be calibrated and validated. The objective of this work is to evaluate the benefits and the limitations of using isotope-derived groundwater travel times and major ion chemistry to validate a regional-scale groundwater flow model in the humid continental climate of southern Québec (Canada). A 3D regional-scale steady-state groundwater model was created using MODFLOW for the fractured bedrock aquifer of the Centre-du-Québec region (Québec, Canada), using data acquired during recent aquifer characterization projects. The model covers an area of 7452 km 2 , from the unconfined Appalachian Mountains to the confined St. Lawrence Platform. Groundwater travel times were simulated for 211 wells using particle tracking. The groundwater flow model was calibrated using 11 775 regionally distributed heads and 15 baseflow values. The model was validated using 23 3 H/ 3 He residence time (3 to 60 years), 17 14 C residence time (226 to 22 600 years), and the major ion compositions from 211 wells. Results indicate that the model is able to satisfactorily simulate ³H/³He isotopic residence time, while 14 C isotopic residence times are generally underestimated. These results suggest substantial mixing between groundwater recharged during the last deglaciation and recently recharged water. Regional groundwater flow is limited or absent, and most of the recharge discharges to the river network as baseflow. The analysis of travel times indicates a statistically distinct mean travel time for the different groundwater types. Median travel time is 68 years for recently recharged groundwater (Ca-HCO3), 274 years for semi-confined groundwater (Na-HCO3), and 738 years for confined groundwater (Na-Cl). This confirms that groundwater chemistry is a broad indicator of groundwater travel time. Résumé La compréhension de la dynamique régionale (> 100 km) de l'eau souterraine est essentielle au développement d'une règlementation orientée vers le développement durable de cette ressource. Les modèles d'écoulement de l'eau souterraine sont de plus en plus utilisés pour supporter ces stratégies. Par contre, pour être utilisés à des fins de règlementation, ces modèles doivent être calés et validés. L'objectif de ce travail est d'évaluer les avantages et les limites de l'utilisation de l'âge isotopique de l'eau souterraine et de la géochimie des ions majeurs pour valider un modèle régional de l'écoulement de l'eau souterraine dans le climat continental humide du sud du Québec (Canada). En utilisant les données acquises dans le cadre de projets de caractérisation hydrogéologiques récents, un modèle 3D régional en régime permanent a été construit avec MODLOW afin de représenter l'aquifère fracturé de la région du Centre-du-Québec (Québec, Canada). Le modèle couvre une superficie de 7 452 km² à partir des zones en nappe libre des montagnes Appalachiennes jusqu'aux secteurs de nappe captive de la plate-forme du Saint-Laurent. Les temps de parcours de l'eau souterraine ont été simulés à 211 puits en utilisant le traçage de particules (MODPATH). Le modèle d'écoulement souterrain a été calé avec 11 775 niveaux distribués dans toute la zone d'étude et avec 15 mesures de débit de bases obtenues à partir de séparation d'hydrogramme ou de mesures manuelles en période d'étiage. Le modèle a ensuite été validé en utilisant les âges isotopiques dérivés de 23 ratios 3 H/ 3 He (entre 3 et 60 ans) et de 17 valeurs de 14 C (entre 226 et 22 600 ans), ainsi qu'avec 211 résultats de géochimie des ions majeurs. Les résultats montrent que le modèle est en mesure de simuler de manière satisfaisante les âges 3 H/ 3 He tandis que les âges 14 C sont généralement sous-estimés. Ces résultats suggèrent un mélange important entre l'eau rechargée durant la dernière déglaciation et l'eau récemment rechargée. Le flux d'eau souterraine régional est faible ou absent et la grande majorité de la recharge retourne au cours d'eau sous forme de débit de base. L'analyse des temps de parcours moyens indique une différence statistiquement significative (α = 0.01) entre les types d'eau souterraine. Le temps de parcours médian est de 165 ans pour les zones de recharge (Ca-HCO3), de 746 ans pour les zones semi-captives (Na-HCO3) et de 7 841 ans pour les zones captives (Na-Cl). Ces résultats montrent bien l'utilité des types d'eau souterraine comme indicateurs généraux des temps de parcours de l'eau souterraine.
Canadian Water Resources Journal / Revue canadienne des ressources hydriques
Groundwater is a crucial supply of freshwater worldwide. It is estimated that groundwater represe... more Groundwater is a crucial supply of freshwater worldwide. It is estimated that groundwater represents more than one third of water withdrawals used for irrigation, domestic, and manufacturing purposes (Döll et al. 2012). In Canada, about 30% of the population (nearly 10 million inhabitants) depend on groundwater for their water supply (CCA 2009). In the Province of Quebec, 20% of the population relies on groundwater for its drinking water over 90% of the inhabited territory (MDDELCC 2018). Globally, several pressures impact the state of groundwater resources, including urbanization, land and water uses, pollution and climate variability (WWAP 2009). The intensification of industrial and agricultural activities, that can lead to contamination and overexploitation, as well as natural climate variability and climate change, are threats to Canada's groundwater (Rivera et al. 2004; CCA 2009). It has been recognized at different levels of organizations that the lack of knowledge on groundwater resources and aquifers, as well as the difficulty in accessing water-related data, are major obtacles to the implementation of sustainable management of groundwater resources (Government of Québec 2002; CCA 2009; WWAP 2009). To face this challenge in the Province of Quebec, a unique and systematic program of regional hydrogeological mapping, the Groundwater Knowledge Acquisition Program (Programme d'acquisition de connaissances sur les eaux souterraines-PACES), was implemented in 2008 by the Québec Ministry of the Environment (Ministère du Développement durable, de l'Environnement et de la Lutte contre les changements climatiques-MDDELCC) to ensure the protection and long-term sustainability of groundwater resources (MDDELCC 2018). The proposed methodology for the PACES program was based on the experience developed during previous hydrogeological mapping projects in Quebec (pre-PACES projects; Figure 1), including the Portneuf granu
ABSTRACT Lorsque les ressources en eaux sont considérées, l’essentiel de notre regard se porte su... more ABSTRACT Lorsque les ressources en eaux sont considérées, l’essentiel de notre regard se porte sur les rivières et lacs. Ce sont les volumes qui nous semblent les plus accessibles. Toutefois, à l’échelle du globe, ce sont bien les eaux souterraines qui contrôlent l’essentiel du cycle de l’eau continental. Ces masses d’eaux qui s’écoulent lentement sous nos pieds représentent 95 % des eaux douces liquides et drainent invariablement les pollutions, qu’elles soient diffuses ou ponctuelles, d’origine anthropique ou « naturelle », vers les cours d’eau. Souvent diffuse et très hétérogène, cette contribution des eaux souterraines aux rivières n’est pas aisée à identifier ou à quantifier. Bien sûr, son intégration à grande échelle a été clairement démontrée par les modèles de bassin développés au cours de la dernière décennie, mais l’identification des mécanismes et processus géochimiques dominants à petite échelle n’est pas simple. Après un rapide rappel sur les méthodes pouvant soutenir une investigation des échanges nappe rivière à petite échelle, nous discuterons des informations apportées par les études de petits bassins versant sur l’importance des milieux humides riverains dans le gain en qualité des eaux de rivières.
Groundwater contribution to river flows, generally called base flows, often accounts for a signif... more Groundwater contribution to river flows, generally called base flows, often accounts for a significant proportion of total flow rate, especially during the dry season. The objective of this work is to test simple approaches requiring limited data to understand groundwater contribution to river flows. The Noire river basin in southern Quebec is used as a case study. A lumped conceptual hydrological model (the MOHYSE model), a groundwater flow model (MODFLOW) and hydrograph separation are used to provide estimates of base flow for the study area. Results show that the methods are complementary. Hydrograph separation and the MOHYSE surface flow model provide similar annual estimates for the groundwater contribution to river flow, but monthly base flows can vary significantly between the two methods. Both methods have the advantage of being easily implemented. However, the distinction between aquifer contribution and shallow subsurface contribution to base flow can only be made with a groundwater flow model. The aquifer renewal rate estimated with the MODFLOW model for the Noire River is 30% of the recharge estimated from base flow values. This is a significantly difference which can be crucial for regional-scale water management. 1 Introduction Providing accurate estimates of groundwater contribution to river flows is important to anticipate possible low flow periods and to evaluate aquifer renewal rates. In temperate and humid climates, groundwater contribution to river flow, generally called base flow, often accounts for a significant proportion of total flow rate, especially during the dry season. Base flows must be estimated to find a compromise between river basin development and maintenance of river ecology (Smakhtin, 2007). Conceptually, a river catchment can be perceived as a series of interlinked reservoirs, each of which has components of recharge, storage and discharge (Smakhtin, 2001). It is very difficult 7810 HESSD 7, 7809-7838, 2010 Groundwater contribution to river flows-southern Quebec aquifer M. Larocque et al.
There is growing concern worldwide about the exposure of groundwater resources to pharmaceuticall... more There is growing concern worldwide about the exposure of groundwater resources to pharmaceutically active compounds (PhACs) and agricultural contaminants, such as pesticides, nitrate, and Escherichia coli. For regions with a low population density and an abundance of water, regional contamination assessments are not carried out systematically due to the typically low concentrations and high costs of analyses. The objectives of this study were to evaluate regional-scale contaminant distributions in untreated groundwater in a rural region of Quebec (Canada). The geological and hydrogeological settings of this region are typical of post-glacial regions around the world, where groundwater flow can be complex due to heterogeneous geological conditions. A new spatially distributed Anthropogenic Footprint Index (AFI), based on land use data, was developed to assess surface pollution risks. The Hydrogeochemical Vulnerability Index (HVI) was computed to estimate aquifer vulnerability. Nine w...
Peat specific yield (S Y) is an important parameter involved in many peatland hydrological 15 fun... more Peat specific yield (S Y) is an important parameter involved in many peatland hydrological 15 functions such as flood attenuation, baseflow contribution to rivers and maintaining 16 groundwater levels in surficial aquifers. However, general knowledge on peatland water 17 storage capacity is still very limited, due in part to the technical difficulties related to in 18 situ measurements. The objectives of this study were to quantify vertical S Y variations of 19 water tables in peatlands using the water table fluctuation method (WTF) and to better 20 understand the factors controlling peatland water storage capacity. The method was tested 21 in five ombrotrophic peatlands located in the St. Lawrence Lowlands (southern Québec, 22 Canada). In each peatland, water table wells were installed at three locations (up-gradient, 23 mid-gradient and down-gradient). Near each well, a 1 m long peat core (8 cm x 8 cm) 24 was sampled, and sub-samples were used to determine S Y with standard gravitational 25 drainage method. A larger peat sample (25 cm x 60 cm x 40 cm) was also collected in 26
Les outils mathématiques sont de plus en plus utilisés pour simuler la contamination d'origin... more Les outils mathématiques sont de plus en plus utilisés pour simuler la contamination d'origine agricole des eaux souterraines. Le modèle AgriFlux permet, à l'aide du module PestiFlux, de simuler les processus responsables du devenir des pesticides dans le sol: ruissellement, volatilisation, adsorption/désorption rapide, adsorption/désorption lente, complexation par la matière organique dissoute, biodégradation en sous-produits, hydrolyse, drainage et lessivage. AgriFlux est utilisé pour simuler le devenir de l'atrazine et du dééthylatrazine sur une parcelle expérimentale de la région de Québec (Québec, Canada) cultivée en maïs sucré (Zea mays, L.) traité à l'atrazine. Des prélèvements d'eau interstitielle ont été réalisés (1986-1990) à l'aide de lysimètres avec succion (0,5 et 1,0 m de profondeur) et analysés pour leur contenu en atrazine et dééthylatrazine. De manière générale, AgriFlux reproduit bien l'évolution des concentrations mesurées, dans le temp...
Peatlands can play an important role in the hydrological dynamics of a watershed. However, intera... more Peatlands can play an important role in the hydrological dynamics of a watershed. However, interactions between groundwater and peat water remain poorly understood. Here, we present results of an exploratory study destined to test radon (222Rn) as a potential tracer of groundwater inflows from fluvioglacial landform aquifers to slope peatlands in the Amos region of Quebec, Canada. 222Rn occurs in groundwater but is expected to be absent from peat water because of its rapid degassing to the atmosphere. Any 222Rn activity detected in peat water should therefore derive from groundwater inflow. 222Rn activity was measured in groundwater from municipal, domestic wells and newly drilled and instrumented piezometers from the Saint-Mathieu-Berry and Barraute eskers (n=9), from the Harricana Moraine (n=4), and from the fractured bedrock (n=3). Forty measurements of 222Rn activity were made from piezometers installed in five slope peatlands, along six transects Highlights Radon measured in eskers and connected peatlands in Quebec Radon is tested as novel tracer of groundwater inflow in peatlands Shallower peat water is depleted in radon by degassing to atmosphere Radon and TDS relation suggests inflow from esker and short residence time *Highlights (for review)
ABSTRACT The estimation of base flow contributions to streamflow, and in particular the partition... more ABSTRACT The estimation of base flow contributions to streamflow, and in particular the partitioning of base flow into shallow and deep aquifer components, is a challenging problem in water resources management. In this study, the newly developed hillslope-storage Boussinesq analytic-element (hsB/AE) model is applied to the Allen River headwater catchment in southern Quebec, Canada, which is a major recharge area for the transboundary Chateauguay River watershed. This first application to a real catchment serves as an illustration of the basic principles behind the coupled model and an investigation into interaquifer interactions and the origins of base flow contributions to streamflow. The hsB component of the model represents local groundwater flow in sloping, shallow Quaternary sediments, whereas the AE component represents the underlying regional bedrock aquifer. The catchment is partitioned into hillslopes of regular convergent, divergent, or combined planform shapes. Simulations are run for the summer periods of 2008 and 2009, and the resulting base flows show good correspondence with estimates on the basis of standard hydrograph separation techniques, in particular, those for low-flow periods from July to September. Overall, satisfactory matches are obtained for the bedrock aquifer heads, but with some underestimation of heads further away from the river. In terms of exchanges between the aquifers, 95% of total leakage is directed toward the bedrock aquifer, whereas only 5% flows in the reverse direction and feeds the hilllsope aquifer, especially in the steeper portion of the catchment. The simulated base flow is partitioned into roughly 65% originating from the shallow hillslope aquifer and 35% from the deep bedrock aquifer, with small interannual variations on the order of 3-5%. This ratio is relatively insensitive to changes in parameter values. For example, a 50% decrease in aquitard thickness reduces the deep bedrock aquifer contribution by only 12%.
The increasing number of studies on the determination of natural methane in groundwater of shale ... more The increasing number of studies on the determination of natural methane in groundwater of shale gas prospection areas offers a unique opportunity for refining the quantification of natural methane emissions. Here methane emissions, computed from four potential sources, are reported for an area of ca. 16,500km(2) of the St. Lawrence Lowlands, Quebec (Canada), where Utica shales are targeted by the petroleum industry. Methane emissions can be caused by 1) groundwater degassing as a result of groundwater abstraction for domestic and municipal uses; 2) groundwater discharge along rivers; 3) migration to the surface by (macro- and micro-) diffuse seepage; 4) degassing of hydraulic fracturing fluids during first phases of drilling. Methane emissions related to groundwater discharge to rivers (2.47×10(-4) to 9.35×10(-3)Tgyr(-1)) surpass those of diffuse seepage (4.13×10(-6) to 7.14×10(-5)Tgyr(-1)) and groundwater abstraction (6.35×10(-6) to 2.49×10(-4)Tgyr(-1)). The methane emission from ...
Soil on sloping bedrock is a common conceptualization in hydrological modeling at the hillslope a... more Soil on sloping bedrock is a common conceptualization in hydrological modeling at the hillslope and subcatchment scales. At these small scales morphology, vegetation, and climate can all be quite accurately represented, whereas pedology and geology are much more difficult to characterize. Thus further approximations, reasoned or ad hoc, are often introduced concerning the prevailing direction(s) of flow, the (im)permeability of
Les tourbières abondent dans l’ensemble du Québec, mais celles de la vallée du Saint-Laurent subi... more Les tourbières abondent dans l’ensemble du Québec, mais celles de la vallée du Saint-Laurent subissent des pressions anthropiques majeures. Ces pressions et les pertes de superficies en tourbières qui en résultent sont à peu près inconnues. Nous avons mesuré la superficie occupée par les tourbières en 1966 et 2010 dans la région de Bécancour et identifié les perturbations récentes qu’elles ont subies à l’aide de la photo-interprétation et de validations sur le terrain. En 2010, les tourbières couvraient 17 500 ha, soit 6,1 % du territoire étudié. De cette superficie, 10 485 ha représentaient des tourbières encore intactes et 7 015 ha des tourbières ayant subi des perturbations limitées, notamment par la présence de canaux de drainage et de chemins forestiers. Entre 1966 et 2010, 5 433 ha de tourbières (près du quart des tourbières présentes en 1966) ont subi des perturbations irréversibles, principalement en raison de la culture de la canneberge (Vaccinium macrocarpon). Cette cultur...
Résumé Même si des travaux récents ont permis de caractériser certains aquifères du sud du Québec... more Résumé Même si des travaux récents ont permis de caractériser certains aquifères du sud du Québec, plusieurs demeurent encore très peu connus. Cette recherche a pour objectifs de comprendre la dynamique de l’écoulement souterrain et la vulnérabilité de l’aquifère du bassin de la rivière Noire (Montérégie, Québec), un bassin représentatif des aquifères de milieux fracturés situés en bordure des Basses-Terres du Saint-Laurent. Dans ce travail, un modèle de bilan hydrique en zone non saturée a permis de quantifier la distribution spatio-temporelle de l’infiltration sur le bassin. L’infiltration simulée moyenne est importante (215 mm•an‑1) et a lieu surtout au moment de la fonte printanière (74 %). L’infiltration la plus élevée se produit dans la partie amont du bassin, mais les résultats du modèle ne permettent pas d’évaluer quelle proportion de la recharge atteint effectivement l’aquifère régional profond. Sur l’ensemble du bassin, les concentrations en nitrate dans l’eau souterraine ...
Dans le cadre de la première et de la troisième phase du Programme d’acquisition de connaissances... more Dans le cadre de la première et de la troisième phase du Programme d’acquisition de connaissances sur les eaux souterraines (PACES) du MDDELCC, deux projets menés par l’Université du Québec à Montréal ont respectivement été lancés aux printemps 2009 et 2012, pour la zone Bécancour (2 924 km2) et la zone Nicolet / Bas-Saint-François (4 585 km2). Ces projets ont pour but d’établir les cartographies hydrogéologiques régionales et sont réalisés avec des partenaires locaux (CRÉ, MRC, municipalités, Agences de géomatique, OBV). Au total, 314 puits (municipaux, résidentiels ou nouvellement forés) ont été d’échantillonnés pour la chimie de l’eau, permettant de déceler 48 dépassements de norme de potabilité, soit pour le baryum (19), l’arsenic (14), le fluor (9), le plomb (2), l’antimoine (1) et l’uranium (1). Les dépassements d’objectifs esthétiques concernent principalement le manganèse (147), la dureté totale (75), le fer (66), et le pH (54). La plupart de ces dépassements seraient d’orig...
In areas where peatlands are abundant, they are likely to play a significant role in the hydrolog... more In areas where peatlands are abundant, they are likely to play a significant role in the hydrological and hydrogeological dynamics of a watershed. Although individual case studies are reported in the literature, there is a large range of aquifer–peatland interactions and there is a need to understand the controls of these interactions. The objectives of this study were (1) to better understand aquifer–peatland connections and how these may be predicted by geology and geomorphic location and (2) to provide a variety of reference sites for glacial geological settings. Slope and depression peatlands were studied in the Abitibi-Témiscamingue region and in the St. Lawrence Lowlands, two contrasting regions of southern Quebec. A total of 12 transects that span a shallow aquifer–peatland interface were instrumented with piezometers. Field investigations included peatland characterization, monthly water level monitoring, and continuous hydraulic head measurements with pressure transducers. ...
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Canadian Water Resources Journal / Revue canadienne des ressources hydriques
Understanding groundwater dynamics at the regional scale (> 100 km) is essential to the developme... more Understanding groundwater dynamics at the regional scale (> 100 km) is essential to the development of sustainable water management regulations. Groundwater flow models are increasingly used to support these strategies. However, in order to be reliable, these models need to be calibrated and validated. The objective of this work is to evaluate the benefits and the limitations of using isotope-derived groundwater travel times and major ion chemistry to validate a regional-scale groundwater flow model in the humid continental climate of southern Québec (Canada). A 3D regional-scale steady-state groundwater model was created using MODFLOW for the fractured bedrock aquifer of the Centre-du-Québec region (Québec, Canada), using data acquired during recent aquifer characterization projects. The model covers an area of 7452 km 2 , from the unconfined Appalachian Mountains to the confined St. Lawrence Platform. Groundwater travel times were simulated for 211 wells using particle tracking. The groundwater flow model was calibrated using 11 775 regionally distributed heads and 15 baseflow values. The model was validated using 23 3 H/ 3 He residence time (3 to 60 years), 17 14 C residence time (226 to 22 600 years), and the major ion compositions from 211 wells. Results indicate that the model is able to satisfactorily simulate ³H/³He isotopic residence time, while 14 C isotopic residence times are generally underestimated. These results suggest substantial mixing between groundwater recharged during the last deglaciation and recently recharged water. Regional groundwater flow is limited or absent, and most of the recharge discharges to the river network as baseflow. The analysis of travel times indicates a statistically distinct mean travel time for the different groundwater types. Median travel time is 68 years for recently recharged groundwater (Ca-HCO3), 274 years for semi-confined groundwater (Na-HCO3), and 738 years for confined groundwater (Na-Cl). This confirms that groundwater chemistry is a broad indicator of groundwater travel time. Résumé La compréhension de la dynamique régionale (> 100 km) de l'eau souterraine est essentielle au développement d'une règlementation orientée vers le développement durable de cette ressource. Les modèles d'écoulement de l'eau souterraine sont de plus en plus utilisés pour supporter ces stratégies. Par contre, pour être utilisés à des fins de règlementation, ces modèles doivent être calés et validés. L'objectif de ce travail est d'évaluer les avantages et les limites de l'utilisation de l'âge isotopique de l'eau souterraine et de la géochimie des ions majeurs pour valider un modèle régional de l'écoulement de l'eau souterraine dans le climat continental humide du sud du Québec (Canada). En utilisant les données acquises dans le cadre de projets de caractérisation hydrogéologiques récents, un modèle 3D régional en régime permanent a été construit avec MODLOW afin de représenter l'aquifère fracturé de la région du Centre-du-Québec (Québec, Canada). Le modèle couvre une superficie de 7 452 km² à partir des zones en nappe libre des montagnes Appalachiennes jusqu'aux secteurs de nappe captive de la plate-forme du Saint-Laurent. Les temps de parcours de l'eau souterraine ont été simulés à 211 puits en utilisant le traçage de particules (MODPATH). Le modèle d'écoulement souterrain a été calé avec 11 775 niveaux distribués dans toute la zone d'étude et avec 15 mesures de débit de bases obtenues à partir de séparation d'hydrogramme ou de mesures manuelles en période d'étiage. Le modèle a ensuite été validé en utilisant les âges isotopiques dérivés de 23 ratios 3 H/ 3 He (entre 3 et 60 ans) et de 17 valeurs de 14 C (entre 226 et 22 600 ans), ainsi qu'avec 211 résultats de géochimie des ions majeurs. Les résultats montrent que le modèle est en mesure de simuler de manière satisfaisante les âges 3 H/ 3 He tandis que les âges 14 C sont généralement sous-estimés. Ces résultats suggèrent un mélange important entre l'eau rechargée durant la dernière déglaciation et l'eau récemment rechargée. Le flux d'eau souterraine régional est faible ou absent et la grande majorité de la recharge retourne au cours d'eau sous forme de débit de base. L'analyse des temps de parcours moyens indique une différence statistiquement significative (α = 0.01) entre les types d'eau souterraine. Le temps de parcours médian est de 165 ans pour les zones de recharge (Ca-HCO3), de 746 ans pour les zones semi-captives (Na-HCO3) et de 7 841 ans pour les zones captives (Na-Cl). Ces résultats montrent bien l'utilité des types d'eau souterraine comme indicateurs généraux des temps de parcours de l'eau souterraine.
Canadian Water Resources Journal / Revue canadienne des ressources hydriques
Groundwater is a crucial supply of freshwater worldwide. It is estimated that groundwater represe... more Groundwater is a crucial supply of freshwater worldwide. It is estimated that groundwater represents more than one third of water withdrawals used for irrigation, domestic, and manufacturing purposes (Döll et al. 2012). In Canada, about 30% of the population (nearly 10 million inhabitants) depend on groundwater for their water supply (CCA 2009). In the Province of Quebec, 20% of the population relies on groundwater for its drinking water over 90% of the inhabited territory (MDDELCC 2018). Globally, several pressures impact the state of groundwater resources, including urbanization, land and water uses, pollution and climate variability (WWAP 2009). The intensification of industrial and agricultural activities, that can lead to contamination and overexploitation, as well as natural climate variability and climate change, are threats to Canada's groundwater (Rivera et al. 2004; CCA 2009). It has been recognized at different levels of organizations that the lack of knowledge on groundwater resources and aquifers, as well as the difficulty in accessing water-related data, are major obtacles to the implementation of sustainable management of groundwater resources (Government of Québec 2002; CCA 2009; WWAP 2009). To face this challenge in the Province of Quebec, a unique and systematic program of regional hydrogeological mapping, the Groundwater Knowledge Acquisition Program (Programme d'acquisition de connaissances sur les eaux souterraines-PACES), was implemented in 2008 by the Québec Ministry of the Environment (Ministère du Développement durable, de l'Environnement et de la Lutte contre les changements climatiques-MDDELCC) to ensure the protection and long-term sustainability of groundwater resources (MDDELCC 2018). The proposed methodology for the PACES program was based on the experience developed during previous hydrogeological mapping projects in Quebec (pre-PACES projects; Figure 1), including the Portneuf granu
ABSTRACT Lorsque les ressources en eaux sont considérées, l’essentiel de notre regard se porte su... more ABSTRACT Lorsque les ressources en eaux sont considérées, l’essentiel de notre regard se porte sur les rivières et lacs. Ce sont les volumes qui nous semblent les plus accessibles. Toutefois, à l’échelle du globe, ce sont bien les eaux souterraines qui contrôlent l’essentiel du cycle de l’eau continental. Ces masses d’eaux qui s’écoulent lentement sous nos pieds représentent 95 % des eaux douces liquides et drainent invariablement les pollutions, qu’elles soient diffuses ou ponctuelles, d’origine anthropique ou « naturelle », vers les cours d’eau. Souvent diffuse et très hétérogène, cette contribution des eaux souterraines aux rivières n’est pas aisée à identifier ou à quantifier. Bien sûr, son intégration à grande échelle a été clairement démontrée par les modèles de bassin développés au cours de la dernière décennie, mais l’identification des mécanismes et processus géochimiques dominants à petite échelle n’est pas simple. Après un rapide rappel sur les méthodes pouvant soutenir une investigation des échanges nappe rivière à petite échelle, nous discuterons des informations apportées par les études de petits bassins versant sur l’importance des milieux humides riverains dans le gain en qualité des eaux de rivières.
Groundwater contribution to river flows, generally called base flows, often accounts for a signif... more Groundwater contribution to river flows, generally called base flows, often accounts for a significant proportion of total flow rate, especially during the dry season. The objective of this work is to test simple approaches requiring limited data to understand groundwater contribution to river flows. The Noire river basin in southern Quebec is used as a case study. A lumped conceptual hydrological model (the MOHYSE model), a groundwater flow model (MODFLOW) and hydrograph separation are used to provide estimates of base flow for the study area. Results show that the methods are complementary. Hydrograph separation and the MOHYSE surface flow model provide similar annual estimates for the groundwater contribution to river flow, but monthly base flows can vary significantly between the two methods. Both methods have the advantage of being easily implemented. However, the distinction between aquifer contribution and shallow subsurface contribution to base flow can only be made with a groundwater flow model. The aquifer renewal rate estimated with the MODFLOW model for the Noire River is 30% of the recharge estimated from base flow values. This is a significantly difference which can be crucial for regional-scale water management. 1 Introduction Providing accurate estimates of groundwater contribution to river flows is important to anticipate possible low flow periods and to evaluate aquifer renewal rates. In temperate and humid climates, groundwater contribution to river flow, generally called base flow, often accounts for a significant proportion of total flow rate, especially during the dry season. Base flows must be estimated to find a compromise between river basin development and maintenance of river ecology (Smakhtin, 2007). Conceptually, a river catchment can be perceived as a series of interlinked reservoirs, each of which has components of recharge, storage and discharge (Smakhtin, 2001). It is very difficult 7810 HESSD 7, 7809-7838, 2010 Groundwater contribution to river flows-southern Quebec aquifer M. Larocque et al.
There is growing concern worldwide about the exposure of groundwater resources to pharmaceuticall... more There is growing concern worldwide about the exposure of groundwater resources to pharmaceutically active compounds (PhACs) and agricultural contaminants, such as pesticides, nitrate, and Escherichia coli. For regions with a low population density and an abundance of water, regional contamination assessments are not carried out systematically due to the typically low concentrations and high costs of analyses. The objectives of this study were to evaluate regional-scale contaminant distributions in untreated groundwater in a rural region of Quebec (Canada). The geological and hydrogeological settings of this region are typical of post-glacial regions around the world, where groundwater flow can be complex due to heterogeneous geological conditions. A new spatially distributed Anthropogenic Footprint Index (AFI), based on land use data, was developed to assess surface pollution risks. The Hydrogeochemical Vulnerability Index (HVI) was computed to estimate aquifer vulnerability. Nine w...
Peat specific yield (S Y) is an important parameter involved in many peatland hydrological 15 fun... more Peat specific yield (S Y) is an important parameter involved in many peatland hydrological 15 functions such as flood attenuation, baseflow contribution to rivers and maintaining 16 groundwater levels in surficial aquifers. However, general knowledge on peatland water 17 storage capacity is still very limited, due in part to the technical difficulties related to in 18 situ measurements. The objectives of this study were to quantify vertical S Y variations of 19 water tables in peatlands using the water table fluctuation method (WTF) and to better 20 understand the factors controlling peatland water storage capacity. The method was tested 21 in five ombrotrophic peatlands located in the St. Lawrence Lowlands (southern Québec, 22 Canada). In each peatland, water table wells were installed at three locations (up-gradient, 23 mid-gradient and down-gradient). Near each well, a 1 m long peat core (8 cm x 8 cm) 24 was sampled, and sub-samples were used to determine S Y with standard gravitational 25 drainage method. A larger peat sample (25 cm x 60 cm x 40 cm) was also collected in 26
Les outils mathématiques sont de plus en plus utilisés pour simuler la contamination d'origin... more Les outils mathématiques sont de plus en plus utilisés pour simuler la contamination d'origine agricole des eaux souterraines. Le modèle AgriFlux permet, à l'aide du module PestiFlux, de simuler les processus responsables du devenir des pesticides dans le sol: ruissellement, volatilisation, adsorption/désorption rapide, adsorption/désorption lente, complexation par la matière organique dissoute, biodégradation en sous-produits, hydrolyse, drainage et lessivage. AgriFlux est utilisé pour simuler le devenir de l'atrazine et du dééthylatrazine sur une parcelle expérimentale de la région de Québec (Québec, Canada) cultivée en maïs sucré (Zea mays, L.) traité à l'atrazine. Des prélèvements d'eau interstitielle ont été réalisés (1986-1990) à l'aide de lysimètres avec succion (0,5 et 1,0 m de profondeur) et analysés pour leur contenu en atrazine et dééthylatrazine. De manière générale, AgriFlux reproduit bien l'évolution des concentrations mesurées, dans le temp...
Peatlands can play an important role in the hydrological dynamics of a watershed. However, intera... more Peatlands can play an important role in the hydrological dynamics of a watershed. However, interactions between groundwater and peat water remain poorly understood. Here, we present results of an exploratory study destined to test radon (222Rn) as a potential tracer of groundwater inflows from fluvioglacial landform aquifers to slope peatlands in the Amos region of Quebec, Canada. 222Rn occurs in groundwater but is expected to be absent from peat water because of its rapid degassing to the atmosphere. Any 222Rn activity detected in peat water should therefore derive from groundwater inflow. 222Rn activity was measured in groundwater from municipal, domestic wells and newly drilled and instrumented piezometers from the Saint-Mathieu-Berry and Barraute eskers (n=9), from the Harricana Moraine (n=4), and from the fractured bedrock (n=3). Forty measurements of 222Rn activity were made from piezometers installed in five slope peatlands, along six transects Highlights Radon measured in eskers and connected peatlands in Quebec Radon is tested as novel tracer of groundwater inflow in peatlands Shallower peat water is depleted in radon by degassing to atmosphere Radon and TDS relation suggests inflow from esker and short residence time *Highlights (for review)
ABSTRACT The estimation of base flow contributions to streamflow, and in particular the partition... more ABSTRACT The estimation of base flow contributions to streamflow, and in particular the partitioning of base flow into shallow and deep aquifer components, is a challenging problem in water resources management. In this study, the newly developed hillslope-storage Boussinesq analytic-element (hsB/AE) model is applied to the Allen River headwater catchment in southern Quebec, Canada, which is a major recharge area for the transboundary Chateauguay River watershed. This first application to a real catchment serves as an illustration of the basic principles behind the coupled model and an investigation into interaquifer interactions and the origins of base flow contributions to streamflow. The hsB component of the model represents local groundwater flow in sloping, shallow Quaternary sediments, whereas the AE component represents the underlying regional bedrock aquifer. The catchment is partitioned into hillslopes of regular convergent, divergent, or combined planform shapes. Simulations are run for the summer periods of 2008 and 2009, and the resulting base flows show good correspondence with estimates on the basis of standard hydrograph separation techniques, in particular, those for low-flow periods from July to September. Overall, satisfactory matches are obtained for the bedrock aquifer heads, but with some underestimation of heads further away from the river. In terms of exchanges between the aquifers, 95% of total leakage is directed toward the bedrock aquifer, whereas only 5% flows in the reverse direction and feeds the hilllsope aquifer, especially in the steeper portion of the catchment. The simulated base flow is partitioned into roughly 65% originating from the shallow hillslope aquifer and 35% from the deep bedrock aquifer, with small interannual variations on the order of 3-5%. This ratio is relatively insensitive to changes in parameter values. For example, a 50% decrease in aquitard thickness reduces the deep bedrock aquifer contribution by only 12%.
The increasing number of studies on the determination of natural methane in groundwater of shale ... more The increasing number of studies on the determination of natural methane in groundwater of shale gas prospection areas offers a unique opportunity for refining the quantification of natural methane emissions. Here methane emissions, computed from four potential sources, are reported for an area of ca. 16,500km(2) of the St. Lawrence Lowlands, Quebec (Canada), where Utica shales are targeted by the petroleum industry. Methane emissions can be caused by 1) groundwater degassing as a result of groundwater abstraction for domestic and municipal uses; 2) groundwater discharge along rivers; 3) migration to the surface by (macro- and micro-) diffuse seepage; 4) degassing of hydraulic fracturing fluids during first phases of drilling. Methane emissions related to groundwater discharge to rivers (2.47×10(-4) to 9.35×10(-3)Tgyr(-1)) surpass those of diffuse seepage (4.13×10(-6) to 7.14×10(-5)Tgyr(-1)) and groundwater abstraction (6.35×10(-6) to 2.49×10(-4)Tgyr(-1)). The methane emission from ...
Soil on sloping bedrock is a common conceptualization in hydrological modeling at the hillslope a... more Soil on sloping bedrock is a common conceptualization in hydrological modeling at the hillslope and subcatchment scales. At these small scales morphology, vegetation, and climate can all be quite accurately represented, whereas pedology and geology are much more difficult to characterize. Thus further approximations, reasoned or ad hoc, are often introduced concerning the prevailing direction(s) of flow, the (im)permeability of
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