Lawrence Lowlands Research Articles

Contrasting rare earth element concentrations and mixing behaviors in the St. Lawrence Estuary and Saguenay Fjord

Rare earth elements (REEs) including Yttrium (Y) are commonly used as tracers of estuarine and oceanic mixing. The lanthanide series and yttrium are usually referred to as REYs. The geochemical behavior of REYs in estuarine environments is generally described as being non-conservative, with large-scale removal by particle scavenging. During mixing, partitioning of these elements occurs according to their source function and the stability of natural complexes, with heavy REEs typically forming more stable complexes than light REEs in solution. In this study, we compare the concentrations and partitioning of the 0.7 μm-filtered and 0.05 μm-filtered fractions of the dissolved REYs collected during the summers of 2017 and 2021 in the surface waters (< 3 m) of the St. Lawrence estuarine system (river, estuary and gulf) with those of the Saguenay Fjord, a tributary of the latter that drains the Mesoproterozoic rocks of the Canadian Shield. Whereas REYs do not mix conservatively in the St. Lawrence Estuary (SLE) in the summer, they nearly do so in the Saguenay Fjord (SF). REY concentrations are 2.5 to 6 times greater in the surface waters of the SF than those of the SLE at the same salinity and, in contrast to most estuaries including the SLE, the fjord waters are enriched in LREEs. The 0.05 μm-filtered REY concentrations are positively correlated with dissolved organic carbon (DOC) and chromophoric dissolved organic matter (CDOM) concentrations in the SF but independent of both DOC and CDOM concentrations in the SLE. The CDOM in the fjord differs from that of the estuary as it is more aromatic and has a higher molecular weight. The formation of strong REE-humate complexes stabilizes REY ions in the SF surface waters and impedes their adsorption to and scavenging by solid surfaces during estuarine mixing. The LREE enrichment in the SF surface waters most likely reflects the geology of the fjord's drainage basin, more specifically the exposed Mesoproterozoic granites and gneisses of the Canadian Shield that are enriched in LREE relative to the younger Paleozoic sedimentary rocks exposed along the St. Lawrence Lowlands.

Regional-Scale Distribution of Helium Isotopes in Aquifers: How Informative Are They as Groundwater Tracers and Chronometers?

This study presents an almost entirely unpublished dataset of 121 samples of groundwater analyzed for helium concentration and its isotopic ratio (3He/4He) in two adjacent watersheds of the St. Lawrence Lowlands, in a region with intensive agricultural activities in the southern Québec Province, Eastern Canada. Most of the samples were collected in the regional bedrock fractured aquifer hosted in mid-Ordovician siliciclastic shales, on a total surface of 7500 km2. Even with this low-density sampling, and in a heterogeneous and fractured aquifer, the helium isotopes bring precious information on the recharge conditions and on chemical evolution of water. The helium spatial interpolation does not show a clear isotopic gradient through the basin. However, it shows progressive enrichment of radiogenic 4He in the confined part of the aquifer. The atmospheric and/or tritiogenic-rich helium occurs at the recharge in the Appalachians and in the middle of the plain, where impermeable cover is limited, and local infiltration of meteoric freshwater reaches the bedrock aquifer. The relation between the total dissolved solids (TDS) and 3He/4He ratios remains elusive. However, on discriminating the samples with the dominant chemistry of water, a clear trend is observed with 3He/4He ratio, suggesting that radiogenic 4He accumulates together with dissolved solids and with increasing time (indicated by progressively older 14C ages). Finally, the noble gas temperatures (NGTs) obtained from concentrations of the other noble gases (Ne, Ar, Kr and Xe) brings constraints on the earlier recharge conditions during the Holocene. Particularly, the NGTs showed that the studied aquifers were continuously replenished, even under ice-sheet cover in the last 10,000 years.

High‐resolution spatiotemporal analysis of hydrologic connectivity in the historical floodplain of straightened lowland agricultural streams

AbstractIn agricultural watersheds, human interventions such as channel straightening have disrupted the hydrologic connectivity between headwater streams and their riparian environment and have thus undermined the ecological services provided by these small streams. Knowledge of the hydrologic connectivity between these streams and their immediate environment (shallow riparian groundwater in the historical floodplain and on adjacent hillslopes) in human‐impacted settings is critical for understanding and restoring these hydrological systems but remains largely incomplete. The objective of this research is to investigate the hydrogeomorphological conditions controlling hydrologic connectivity in the historical floodplain of straightened lowland streams. Detailed measurements on the spatiotemporal variability of groundwater‐surface water interactions between straightened reaches, historical floodplain including abandoned meanders, and the adjacent hillslopes were obtained using a dense network of piezometers at two sites in the St. Lawrence Lowlands (Quebec, Canada). Results show that the complex mechanisms controlling hydrologic connectivity in naturally meandering lowland rivers also operate in highly disturbed straightened reaches, despite backfilling and agricultural practices. The pre‐straightening hydrogeomorphological configuration of the floodplain partly explains the complex patterns of piezometric fluctuations observed at the sites. The apex of the abandoned meanders stands out as a focal area of hydrologic connectivity as water levels indicate pressure transfer that may reflect flows from the stream, the hillslopes, and the surrounding historical floodplain. These unique field observations suggest that abandoned meanders should be promoted as key elements of restoration strategies in lowland agricultural straightened headwater streams.

Impact of Soil Characteristics and Weed Management Practices on Glyphosate and AMPA Persistence in Field Crops Soils from the St. Lawrence Lowlands (Quebec, Canada)

The use of glyphosate-based herbicides (GBHs) in industrial agriculture has intensified in the past decades, causing a growing concern about the occurrence and spatial distribution of glyphosate and its principal metabolite, aminomethylphosphonic acid (AMPA), in the environment. In 2014, glyphosate and AMPA content was measured in 45 soils from the St. Lawrence Lowlands (Quebec, Canada) before seeding and at harvest in soybean field crops using various weed management practices with or without GBH applications. At the same time, a recent history of agricultural practices and soil conditions was compiled for the sampled sites. The results of the study show that 91% of the samples contained detectable amount of either glyphosate or AMPA, with maximum values of 0.47 mg·kg−1 and 1.16 mg·kg−1 for glyphosate and AMPA, respectively. Surprisingly, detectable amounts of AMPA were measured in fields not treated with GBHs in 2014, whereas traces of both glyphosate and AMPA were detected in organic field crops, highlighting the potential spreading and/or persistence of both compounds in the environment. Glyphosate content was significantly higher in clay soils rich in exchangeable cations, such as Mg2+, K+ and Ca2+, which can contribute to the retention of glyphosate in soil via complexation processes.

Characteristics of Precambrian basement intruded by Cretaceous geological intrusions in Monteregian Igneous Province and their impacts on regional thermal structure

With the progress of geothermal exploration in deep buried geological bodies, high radiogenic geological intrusions have become the hot spot in recent years. However, the assessment of the complex structure, lithology of geological intrusions by the geophysical methods has uncertainty, making it a challenging to accurately predict the thermal structure around the geological intrusions. In southern Québec, Canada, recent studies show that a relative high surface heat flux has been detected in the region enclosed by Montréal, Salaberry-de-Valleyfield and Saint-Jean-sur-Richelieu, around the southwest of the Monteregian Hills, which belong to the Early Cretaceous alkaline and carbonatite intrusions. It is not clear whether these Monteregian intrusions have impacts on the thermal anomaly of the Montréal, Salaberry-de-Valleyfield and Saint-Jean-sur-Richelieu region. The objective of this paper is to numerically investigate the thermal structure in the thermal anomaly region, considering the impact of different Monteregian intrusions. The simplified Monteregian intrusions are embedded into a three-dimensional geological model consisting of the sedimentary formations in the St. Lawrence Lowlands and the simulator Underworld2 is used for the thermal modelling. Simulation results show that the geological intrusions in this region have large impacts on the thermal structure at the local-scale, depending on the radiogenic heat production, thermal conductivity, emplacement depth and size. Temperature in the sedimentary formations may be lower or higher than that of the adjacent geological intrusions, highly depending on the thermal physical characteristics of these intrusions. Furthermore, the complex fault systems also strongly control the thermal distribution in different fault blocks, making the Potsdam Group sandstone located between the Grand-St-Esprit and Notre-Dame-du-Bon-Conseil faults as the potential geothermal reservoir. Cited as: Liu, H., Ban, S., Bédard, K., Giroux, B. Characteristics of Precambrian basement intruded by Cretaceous geological intrusions in Monteregian Igneous Province and their impacts on regional thermal structure. Advances in Geo-Energy Research, 2022, 6(3): 206-220. https://doi.org/10.46690/ager.2022.03.04

Depth–Sequential Investigation of Major Ions, δ18O, δ2H and δ13C in Fractured Aquifers of the St. Lawrence Lowlands (Quebec, Canada) Using Passive Samplers

General and isotopic geochemistry of groundwater is an essential tool to decipher hydrogeological contexts and flow paths. Different hydrogeochemical patterns may result from the inherent physical aquifer heterogeneity, which may go unnoticed without detailed investigations gathered from multilevel or multiple observation wells. An alternative to overcome the frequent unavailability of multiple wellbores at sites is to perform a detailed investigation on the single wellbore available. In this perspective, the aim of this study is to use passive samplers to sequentially collect groundwater at depths in long–screened wellbores. Such investigation is carried out for major ions and stable isotopes compositions (δ2H, δ18O, δ13C) at ten sites in the context of fractured carbonate aquifers of the St. Lawrence Lowlands (Quebec, Canada). The information gathered from the calco–carbonic system, major ions and stable isotopes report poorly stratified and evolved groundwater bodies. Contribution of water impacted by anthropogenic activities, such as road salts pollution and carbon sources from C4 vegetation, when they occur, are even observed at the greatest depths. Such observations suggest quick flow paths and efficient mixing conditions, which leads to significant contributions of contemporary groundwater bodies in the fractured aquifers investigated down to depths of about 100 m. Although physical aquifer investigation reported few and heterogeneously distributed fractures per wellbore, hydrogeochemical findings point to at overall well interconnected fracture networks in the aquifer and high vulnerability of groundwater, even at significant depths.

Microstructural Analyses of Cement-Based Binders in Stabilizing Champlain Sea Clay

This research investigated the strength development and the microstructural change in Champlain Sea clay when treated with five different cement-based binders. Champlain Sea clay, a marine clay, is commonly found in St. Lawrence Lowlands in eastern Canada. The unconfined compressive strength tests were conducted to measure the shear strength development of treated clay under different binder type, binder dosage, and curing time conditions. The scanning electronic microscopy (SEM) and X-ray diffraction (XRD) analyses were conducted to investigate the microstructural changes in the specimens. Based on the test results, it was found that cement is efficient to treat Champlain Sea clay with a significant strength improvement. For Champlain Sea clay used in this study, the optimum cement dosage was found to be around 100 kg/m3 per mixed volume in terms of strength improvement and cost-effectiveness. The clay samples treated with a mix of cement and cement kiln dust and a mix of cement with slag showed a substantial strength increase over time. These results proved the feasibility of using cement kiln dust mix or slag to replace a portion of cement in treating Champlain Sea clay. Based on SEM observations, a substantial transformation was observed in the microstructure of the clay due to cement mixing. A large amount of clay-binder aggregates were formed and the hydration products filled the porous network of the clay samples, which results in a strength improvement in the treated clay. Based on the XRD analysis, hydration products, such as calcium silicate hydrate and calcium tecto-dialumodisilicate tetrahydrate, were formed in the cement-treated clay specimens, which explains the strength improvement of Champlain Sea clay due to cement mixing.

Hydrogeology of a complex Champlain Sea deposit (Quebec, Canada): implications for slope stability

The thick sequences of marine clayey deposits that blanket the St. Lawrence Lowlands in south-eastern Canada are highly susceptible to landslides. With 89% of the population of the province of Quebec living in this region, improving our understanding of the mechanisms causing landslides in these sediments is a matter of public security. To accomplish this goal, instruments were deployed at a field site in Sainte-Anne-de-la-Pérade, Quebec, Canada to monitor atmospheric, soil, and groundwater conditions. Field and laboratory measurements of soil geotechnical and hydraulic properties were also performed. Results indicate that the groundwater and pore pressure dynamics at the site cannot be explained using simplified site conceptual models. Further analysis indicates that groundwater dynamics and pore pressures in the massive clay deposits on site are determined by (i) the highly heterogeneous nature of the local geological materials, (ii) the contrasting hydraulic and geotechnical properties of these materials, (iii) the presence of two unconfined aquifers at the site, one surficial and one at depth, and (iv) the presence of the Sainte-Anne River. These results were used to create a new conceptual model that illustrates the complex groundwater flow system present on site and shows the importance of including hydrogeologic context in slope stability analysis.

Determination of sediment sources in a mixed watershed within the Appalachian-St. Lawrence Lowland Regions of southern Quebec using sediment fingerprinting.

This paper identifies the main sediment sources to the Beaudet Reservoir in Quebec (Canada) using sediment fingerprinting. The reservoir, which is built on the Bulstrode River and provides drinking water to Victoriaville, has decreased in capacity by 35% in the past 35 years. This study provides new data on fingerprinting in large and complex watersheds, a first in the province of Quebec. Nine sampling sites on the Bulstrode River and its three main tributaries were selected and five sampling campaigns were conducted. Samples from river bank profiles and adjacent fields, along with suspended sediments, were collected. All samples were sieved to 2 mm and analyzed for 137Caesium, 15 geochemical elements and sieved to 63 μm for color analysis. Source classification, based on an ANOVA test to verify the independence hypothesis and iterative linear discriminant analysis to optimize the ratio of inter-group/within-group variability, resulted in four sample classes: agricultural soils, forested soils, stream bank bottom and stream bank top. A Kruskal-Wallis H test then identified 21 out of the 32 tracers with p value < 0.05. The linear discriminant analysis led to a set of 14 tracers, namely 137Cs and 13 color coefficients with a discriminating result of 94%. That combination of 137Cs and color coefficients proved to be a cost-effective fingerprint. Based on MixSIAR modeling results, this sediment fingerprinting study has demonstrated that the main sediment sources varied within the watershed but, generally, forested soil particles dominated (33 to 49%), then agricultural soils (43 to 50%) reflecting the land use changes, followed by stream bank bottoms (82%) at the Beaudet Reservoir.

Deep geothermal resource assessment of the St. Lawrence Lowlands sedimentary basin (Québec) based on 3D regional geological modelling

Geothermal resource quantification requires underground temperature and volume information, which can be challenging to accurately assess at the regional scale. The analytical solution for steady-state heat conduction with internal heat generation is often used to calculate temperature at depth, while geological models can provide volume information. Both approaches were originally combined in a single 3D geological model, in which the underground temperature is directly computed, to accurately evaluate geothermal resources suitable for power generation in the St. Lawrence Lowlands sedimentary basin covering 18,000 km2 in Quebec, Canada, and improve methods for geothermal resource quantification. This approach, used for the first time at such a large scale, allowed to determine the volume of each thermal unit providing a detail assessment of resource depth, temperature and host geological formation. Only 5% of geothermal resources at a temperature above 120 °C that is suitable for power generation were shown to be hosted in the Cambro-Ordovician sedimentary rock sequences at a depth of 4 to 6 km, while 95% of the resource is hosted by the underlying Precambrian basement.

Mantle helium in Southern Quebec groundwater: A possible fossil record of the New England hotspot

The Monteregian Hills are an alignment of magmatic intrusions of Cretaceous age located in the St. Lawrence Lowlands, Quebec, Canada. Their origin is controversial and numerous studies have failed to decipher between a hotspot trail or sub-continental magmatism related to the opening of the North Atlantic Ocean. Here, we show that 17.7±9.6% of the helium of the modern to Holocene-aged groundwater from the regional aquifer is of mantle origin, with a 3He/4He (R) of up to 1.42 times the atmospheric ratio (Ra). It suggests that a fossil Monteregian Hills magmatic signal, diluted by local radiogenic helium and preserved in the Monteregian Hills intrusions, is leached locally by flowing modern or sub-modern groundwater. Helium isotopic measurements by pyrolysis in Monteregian Hills bulk rocks and clinopyroxene separates show R/Ra values of up to 4.96, suggesting that fossil mantle helium has been partially preserved in these rocks and their mineral phases. Monte Carlo simulations of a magma aging model shows that the initial 3He/4He ratio in these Cretaceous intrusions could have been between 21±10Ra and 33±28Ra (2σ), favoring the hypothesis that the Monteregian Hills are the product of the passage of the North American plate over the New England hotspot. This study raises the prospect of using modern groundwater as an archive of mantle He over a hundreds of millions of years timescale.

Role of Cluster Validity Indices in Delineation of Precipitation Regions

The delineation of precipitation regions is to identify homogeneous zones in which the characteristics of the process are statistically similar. The regionalization process has three main components: (i) delineation of regions using clustering algorithms, (ii) determining the optimal number of regions using cluster validity indices (CVIs), and (iii) validation of regions for homogeneity using L-moments ratio test. The identification of the optimal number of clusters will significantly affect the homogeneity of the regions. The objective of this study is to investigate the performance of the various CVIs in identifying the optimal number of clusters, which maximizes the homogeneity of the precipitation regions. The k-means clustering algorithm is adopted to delineate the regions using location-based attributes for two large areas from Canada, namely, the Prairies and the Great Lakes-St Lawrence lowlands (GL-SL) region. The seasonal precipitation data for 55 years (1951–2005) is derived using high-resolution ANUSPLIN gridded point data for Canada. The results indicate that the optimal number of clusters and the regional homogeneity depends on the CVI adopted. Among 42 cluster indices considered, 15 of them outperform in identifying the homogeneous precipitation regions. The Dunn, D e t _ r a t i o and Trace( W − 1 B ) indices found to be the best for all seasons in both the regions.

An exploratory data analysis approach for assessing the sources and distribution of naturally occurring contaminants (F, Ba, Mn, As) in groundwater from southern Quebec (Canada)

The presence of naturally occurring contaminants in groundwater is a public health concern in rural areas of northeastern North America, where public and private wells are important sources of drinking water. In southern Quebec (Canada), inorganic groundwater chemistry data have been recently collected following standard procedures in several regional hydrogeological projects implemented by the government of Quebec. In this study, a groundwater chemistry database was compiled from 16 regional projects altogether covering an area of approximately 100,000 km2. The database includes information on water supply infrastructures, geological settings, hydrogeological conditions and inorganic water chemistry for 2369 water samples. Samples were mostly collected from private domestic wells, and to a lesser extent from municipal and observation wells. The data revealed that fluoride, barium, manganese and arsenic are the most common elements exceeding Canadian drinking water guidelines. Exploratory data analysis techniques were applied to selected subsets of data to gain insight into the sources and distribution of these hazardous groundwater contaminants. These exploratory methods include graphical data analysis (maps, Piper and empirical cumulative distribution function plots), multivariate compositional data analysis (clustering and correlation analysis) and geochemical modeling (saturation index calculations). The results suggest that fluoride, barium, manganese and arsenic are all derived from natural sources. Elevated fluoride concentrations are mainly associated with dilute Ca–Na–HCO3 bedrock groundwaters from granitic areas (Grenville Province), and more geochemically evolved Na–HCO3 to Na–HCO3–Cl bedrock groundwaters from shale areas (St. Lawrence Platform). High-F groundwaters are generally characterized by low Ca concentrations (<30 mg/L) and alkaline pH (pH > 8), suggesting that F is mainly controlled by fluorite (CaF2) precipitation and anion exchange with OH−. Barium is present at elevated concentrations in mineralized Ca–Na–HCO3, Na–HCO3 to Na–HCO3–Cl waters from bedrock aquifers of the St. Lawrence Lowlands. These groundwaters are mainly chemically evolved, strongly reducing waters occurring in confined aquifers and near major faults, which appear to correspond to discharge areas for deep regional flow. High Ba concentrations are generally associated with very low SO4 concentrations (< 5 mg/L) resulting from sulfate reduction, suggesting a solubility control of Ba through barite (BaSO4) precipitation. Most high manganese concentrations occur in less chemically evolved, near-neutral Ca–HCO3 groundwaters from both granular and bedrock aquifers, particularly those associated with metasedimentary and metavolcanic lithologies (Superior Province, St. Lawrence Platform and Appalachian Province). The results suggest that dissolved Mn concentrations are limited by the precipitation of Mn carbonates under alkaline conditions, but increase under reducing conditions owing to the dissolution of Fe–Mn oxyhydroxides. Elevated arsenic concentrations were mostly found in Ca-(Na–Mg)–HCO3 bedrock groundwaters of the Superior and Appalachian Provinces. As-rich groundwaters are associated with the presence of As-bearing sulfides in weakly metamorphosed sedimentary rocks (shale, slate, phyllite) and hydrothermally altered rocks. Most high As concentrations do not appear to be directly derived from sulfide oxidation, but rather from secondary sources, in particular through the reductive dissolution of As-rich Fe–Mn oxyhydroxides. This work shows that the combination of graphical, multivariate statistical and geochemical modeling techniques is a powerful approach to explore large hydrochemical datasets. It also reveals the benefits of using multivariate compositional data analysis instead of classical approaches based on raw data and log-ratios for groundwater chemistry data. Compositional data analysis techniques improved the detection of multivariate outliers, the cluster reliability in cluster analysis, and removed the spurious positive correlation between hydrochemical variables associated with total mineralization.

The successful experience of IGCP636 project “Unifying international research forces to unlock and strengthen geothermal exploitation of the Americas and Europe”

Geothermal fluids are extracted through deep wells drilled in a geological reservoir, which can be represented by highly heterogeneous volcanic complex, sedimentary basins or deep basement rocks. The main objective of this project was to propose suitable methodologies and techniques for the characterization and modeling of fractured geothermal reservoirs, to ensure their sustainable exploitation and, therefore, ensure acceptation of this kind of energy by local communities. This goal was achieved with experiences from the volcanic complex of the Nevado del Ruiz (Colombia), the St. Lawrence Lowlands sedimentary basin (Quebec, Canada), the Carboniferous limestone reservoir in the area of Mons (Belgium), the Soultz-Sous-Forets power plant and the Ploemeur fractured rock hydrogeological experimental site (France), and various areas of interest for geothermal exploration in Chile. The work conducted provided new insights into the construction of conceptual and numerical models for geothermal reservoirs and allowed the creation of a solid research network between Europe and Americas, fostering participation in geosciences of young researchers, students, and women.

A workflow for bedrock thermal conductivity map to help designing geothermal heat pump systems in the St. Lawrence Lowlands, Québec, Canada

An accurate knowledge of the subsurface thermal conductivity is essential to design geothermal heating and cooling systems, specifically ground-coupled heat pumps. The subsurface thermal conductivity has a direct impact on the length of vertical ground heat exchangers needed to fulfill building energy needs. However, mapping the distribution of the subsurface thermal conductivity is a significant challenge due to the ground heterogeneity and the limited radius of influence associated with thermal conductivity assessment methods. Data from 79 thermal response tests, 90 thermal conductivity analyses conducted in the laboratory, and geophysical well logs from 72 oil and gas exploration wells were combined and analyzed together in an attempt to map the bedrock thermal conductivity distribution of the St. Lawrence Lowlands, Québec, Canada. Results from laboratory and well log analysis were adjusted for field scale-effects using thermal response tests to properly define a statistically reliable thermal conductivity for each thermostratigraphic unit of this sedimentary basin. The thermal conductivity obtained from thermal response tests and adjusted laboratory analyses was interpolated with sequential Gaussian simulations to generate a two-dimensional bedrock thermal conductivity map, which can be used by geothermal system designers to better understand the geothermal heat pump potential of the St. Lawrence Lowlands.

Construction of Deep Thermal Models Based on Integrated Thermal Properties Used for Geothermal Risk Management

The development of deep geothermal energy may be at risk from the economic point of view if the estimated deep thermal field is far from its real state. The strong heterogeneity of geological units makes it challenging to perform a reliable estimation on the construction of the deep thermal field over a large region. Additionally, the thermal properties of rocks, such as thermal conductivity and the radiogenic element concentration, whether they are from laboratory measurements or inversed from well logs, may strongly control the deep thermal field at a local scale. In this paper, the thermal conductivities of rocks from the Trois-Rivieres region in the Saint Lawrence Lowlands sedimentary basin in eastern Canada are obtained from two methods: (i) direct experimental measurement and (ii) indirect inversionmethod using well logs, including gamma ray, neutron porosity, density, and photoelectric absorption factor. The spatial distribution of subsurface temperature in the study area in the Trois-Rivieres region is numerically investigated by considering four case studies that include different values (minimum, average, and maximum) of the thermal properties by applying the Underworld simulator. The results show that thermal properties play a large role in controlling the subsurface temperature distribution and heat flux. The temperature difference can reach 15 °C in the basement, caused by the difference in thermal properties in the Trois-Rivieres region. The highest heat flux is found in the Trenton–Black River–Chazy groups, and the lowest heat flux is in the Potsdam group, which also has the highest thermal conductivity. Vertical heat flux does not change linearly with depth but is highly related to the thermal properties of specific geological formations. Furthermore, it does not have a positive correlation with the vertical temperature changes. This demonstrates that the assessment of the potential of deep geothermal energy depending merely on the surface heat flux may greatly overestimate or underestimate the geothermal capacity. Construction of the thermal models based on the integrated thermal properties from both the experimental measurement and well logs in this paper is useful in reducing the exploration risk associated with the utilization of deep geothermal energy.

Potential Efficiency of Grassy or Shrub Willow Buffer Strips against Nutrient Runoff from Soybean and Corn Fields in Southern Quebec, Canada.

Riparian buffer strips (RBS) are encouraged to control agricultural diffuse pollution. In Quebec Province, Canada, a policy promotes 3-m-wide RBS. Abiding farmers minimally maintain herbaceous vegetation, but nutrient retention efficiency could be improved with woody biomass. This work aimed to assess if fast-growing willows ( Seemen 'SX64') could reduce nutrient loads to a stream, in addition to yielding biomass. Triplicate treatments of two stem densities and a herbaceous control plot were monitored from 2011 to 2013 in a randomized block design on agricultural fields of the St. Lawrence Lowlands with sandy loam (Saint-Roch-de-l'Achigan [SR]) and organic-rich (Boisbriand [BB]) soils. Runoff, interstitial water, and water from the saturated zone were sampled 16 (SR) and 14 (BB) times to quantify nutrient buffering (NO, NH, P, and K). Sampling campaigns followed (i) snowmelt or ≥15-mm natural precipitation events after (ii) fertilization and (iii) glyphosate-based herbicide applications. Concentration reduction before and after the RBS was highest for nitrates (77-81% in runoff at BB, 92-98% at 35- to 70-cm depth at SR) just after fertilization, when edge-of-field concentrations peaked. Total P removal was observed in runoff after fertilization at SR, and K removal was punctually witnessed at BB. Riparian buffer strips were inefficient for NH and dissolved P removal, and RBS effluents exceeded aquatic life protection standards. plantations, irrespective of stem density, were not more efficient than herbaceous RBS. This shows that without fertilizer input reductions, narrow RBS are insufficient to protect streams from excess nutrients in corn ( L.) and soybean [ (L.) Merr.] crops.

Allochthonous sources of iodine and organic carbon in an eastern Ontario aquifer

Regional geochemical characterization of groundwaters in a bedrock aquifer in the Ottawa – St. Lawrence Lowlands of eastern Ontario has identified an iodine (I) anomaly, with values regularly exceeding 150 μg/L and a maximum observed concentration of 10 812 μg/L. The spatial distribution, enrichment mechanisms, and sources of I and organic matter were investigated using geochemical and isotopic data. High-I groundwaters (&gt;150 μg/L) are prevalent in Na–Cl-type groundwaters at low bedrock elevations in areas overlain by thick layers of glacial sediments. I is thought to be linked to massive muds in the glacial sediments overlying the aquifer, deposited during the postglacial incursion of the Champlain Sea 12–10 ka BP. Principal component analysis of I and 18 other chemical parameters revealed correlations among I, salinity, and indicators of microbial oxidation of organic matter, suggesting that the intrusion of saline pore waters affected by decomposition of organic matter such as marine phytoplankton in the massive muds is the dominant process controlling I enrichment in groundwater. 129I/127I ratios in the pre-modern waters vary between near-marine values of 460 × 10−14 and 5 × 10−14, demonstrating that older allochthonous I derived from the surrounding Paleozoic sedimentary terrain also contributed to the I pool in the Champlain Sea basin. 14C ages and δ13C signatures for dissolved organic carbon in groundwater and disseminated organic carbon within the glaciomarine muds highlight an allochthonous source of terrestrial organic carbon predating the Champlain Sea incursion, likely transported via glacial meltwaters in tandem with I to the Champlain Sea basin.

Ecological Engineering for the Protection of Stream Banks in Quebec: Inventory and Prospects for the St. Lawrence Lowlands

Ecological Engineering for the Protection of Stream Banks in Quebec: Inventory and Prospects for the St. Lawrence Lowlands

Numerical analysis of the role of radiogenic basement on temperature distribution in the St. Lawrence Lowlands, Qu\xe9bec

Regions with low or medium surface heat flow in stable cratonic areas, such as in eastern Canada, have received little attention for geothermal energy. In the presence of a high heat-producing basement overlain by a sedimentary cover, however, such areas might be prospective. Their potential will depend on various parameters such as heat production within the basement, thermal conductivity of sedimentary formations, and structural context. In this study, we aim at quantifying the importance of these parameters on temperature distribution at depth for a model representative of the St. Lawrence Lowlands, Québec, where locally anomalously higher heat flow has been observed and a 3D model of sedimentary cover is available. Scenarios involving physical properties from neighbouring Grenvillian domains are considered: Portneuf–Mauricie domain with radiogenic heat production of 0.94–5.83 upmu hbox {W m}^{-3}, 0.02–4.13 upmu hbox {W m}^{-3} for the Morin Terrane, and 0.34–1.96 upmu hbox {W m}^{-3} for the Parc des Laurentides domain. The impact of radiogenic heating on temperature distribution at depth was simulated using the Underworld2 numerical modeling code. Results show that at 5 km depth, the range of temperature difference is 22 °C for all modeled scenarios. In addition, the benefit of the thermal blanket effect of the sedimentary cover can be significant, but depends strongly on the contrast in thermal conductivity between the basement and the cover, as well as on the structural context, and less on heat production in the basement. Finally, depth of the 120 °C isotherm varies by up to 1 km for the scenarios considered; carefully assessing the boundary conditions therefore, appears critical in an exploration context.