Center Eau Terre Environnement

Québec, Canada

Center Eau Terre Environnement

Québec, Canada
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Bourgault D.,University of Quebec at Rimouski | Hamel C.,Université de Sherbrooke | Cyr F.,University of Quebec at Rimouski | Tremblay J.-E.,Laval University | And 3 more authors.
Geophysical Research Letters | Year: 2011

Turbulence and nitrate measurements collected in the Amundsen Gulf during ice-covered conditions in fall 2007 are combined to provide mean vertical profiles of eddy diffusivity K̄ and diffusive nitrate fluxes F̄. The mean diffusivity (with 95% confidence intervals) was maximum near the uppermost sampling depth (10 m) with K̄max = 3(2, 5) × 10 -3 m2 s-1 and decreased exponentially to a depth of ∼50 m, below which it was roughly constant at the background value K$\overline{b = 3(2, 5) × 10-6 m2 s-1. The nitracline, centered around 62 m depth, was subject to an eddy diffusivity close to the background value K̄b and the mean diffusive nitrate flux across the nitracline was F̄nit = 0.5(0.3, 0.8) mmol m-2 d-1. These observations are compared with other regions and the role of vertical mixing on primary production in the Amundsen Gulf is discussed. Copyright 2011 by the American Geophysical Union.

Perozzi L.,Center Eau Terre Environnement | Gloaguen E.,Center Eau Terre Environnement | Rondenay S.,Massachusetts Institute of Technology | McDowell G.,Vale Inc.
Journal of Applied Geophysics | Year: 2012

Modeling of grades is a key step and the major source of error in appraisal stage of mining projects. We used a geostatistical approach to explicitly integrate seismic travel time data, as well as acoustic and core logging data into the estimation of nickel grades in the Voisey's Bay deposit. Firstly, the crosshole seismic travel times are inverted using a stochastic tomographic algorithm. This algorithm allows for the inclusion of acoustic log data and seismic covariance into the inverse problem, leading to high-resolution velocity tomographic images of the orebody. Secondly, grade realizations are generated using a Bayesian sequential Gaussian simulation algorithm, which integrates the ore grades measured on the core logs and the previously inverted tomographic data. The application of the presented method to the Voisey's Bay deposit yields an improved knowledge of the geology setting and generates grade models with realistic spatial variability compared to conventional methods. © 2011 Elsevier B.V.

Franssen J.,McGill University | Blais C.,University of Quebec at Trois - Rivieres | Lapointe M.,McGill University | Berube F.,Center Eau Terre Environnement | And 2 more authors.
Canadian Journal of Fisheries and Aquatic Sciences | Year: 2012

We investigated the distinct physical controls causing entombment and asphyxiation, the key mechanisms influencing salmonid egg-to-emergence (EtE) survival. Entombment occurs when sediment blocks the interstitial pathways (macropores) that larvae use to emerge from the streambed, while asphyxiation is related to low oxygen flux, which is a function of interstitial flow velocity. EtE survival has been related to substrate composition and flow velocity. However, in streambed sediments these variables are correlated, and few studies have examined the sensitivity of EtE survival to changes in velocity and oxygen flux at fixed substrate composition. EtE survival has not yet been directly related to the size and density of macropores. We incubated brook trout (Salvelinus fontinalis) embryos in artificial redds with different sediment compositions and hydraulic gradients to examine independently the effects of substrate composition, macropore geometry, and flow velocity on EtE survival, emergence timing, and fry condition. In situ measurements of macropore size were obtained using a computed tomography scanner. Despite high oxygen concentrations, we observed that entombment or blockage effects caused high embryo mortality in fines-rich substrates with few large macropores, and triggered early emergence of rare survivors. These outcomes could not be mitigated by increased flow velocity and oxygen flux to the egg pocket.

Dribault Y.,Center Eau Terre Environnement | Dribault Y.,Laval University | Chokmani K.,Center Eau Terre Environnement | Bernier M.,Center Eau Terre Environnement | Bernier M.,Laval University
Remote Sensing | Year: 2012

The La Grande River watershed, located in the James Bay region (54°N, Quebec, Canada), is a major contributor to the production of hydroelectricity in the province. Peatlands cover up to 20% of the terrestrial environment in this region. Their hydrological behavior is not well understood. The present study is part of a multidisciplinary project which is aimed at analyzing the hydrological processes in these minerotrophic peatlands (fens) in order to provide effective monitoring tools to water managers. The objective of this study was to use VHR remote sensing data to understand the seasonal dynamics of the hydrology in fens. A series of 10 multispectral pan-sharpened GeoEye-1 images (with a spatial resolution of 40 cm) were acquired during the snow-free season (May to October) in 2009 and 2010, centered on two study sites in the Laforge sector (54°06'N; 72°30'W). These are two fens instrumented for continuous hydrometeorological monitoring (water level, discharge, precipitation, air temperature). An object-based classification procedure was set up and applied. It consisted of segmenting the imagery into objects using the multiresolution segmentation algorithm (MRIS) to delineate internal structures in the peatlands (aquatic, semi-aquatic, and terrestrial). Then, the objects were labeled using a fuzzy logic based algorithm. The overall classification accuracy of the 10 images was assessed to be 82%. The time series of the peatland mapping demonstrated the existence of important intra-seasonal spatial dynamics in the aquatic and semi-aquatic compartments. It was revealed that the dynamics amplitude depended on the morphological features of the fens. The observed spatial dynamics was also closely related to the evolution of the measured water levels. © 2012 by the authors.

Fayol N.,Succ Center Ville | Jebrak M.,Succ Center Ville | Harris L.B.,Center Eau Terre Environnement
Precambrian Research | Year: 2016

Exploration for Neoarchean intrusion-related gold deposits in the Abitibi greenstone belt of the Superior Craton, Canada, is of increasing interest as the two most recent Abitibi gold mines are intrusion-related. Late-Archean alkaline intrusions in the Abitibi Subprovince are separated into three groups based on their geophysical and geochemical signatures: (1) large, heterogeneous, unmineralized plutons; (2) small magnetite rich-syenites with magmatic gold, which is often remobilized along fault arrays; (3) small magnetite poor-quartz-syenites to alkali granites with magnetite-rich halos and magmatic gold mineralization. The positive, aeromagnetic high centred signature of some gold-bearing intrusions is related to the high content in magnetite of the more ferromagnesian intrusions resulting from their magmatic evolution. Intrusions with an annular shape record a lower Fe2O3t content in their less magnetite-rich cores and gold mineralization occurs within their magnetite-rich metasomatized host-rocks. If the aeromagnetic signature has an annular-shape, the lower-magnetic zones in the magnetic aureole are the more favourable zones. For those with a positive magnetic signature, the intrusion itself is the target. © 2016 Elsevier B.V.

Ji J.,Beijing Forestry University | Ji J.,Montpellier University | Kokutse N.,CIRAD - Agricultural Research for Development | Kokutse N.,Center Eau Terre Environnement | And 3 more authors.
Catena | Year: 2012

Vegetation is widely used for controlling shallow landslides. The mechanisms by which roots increase apparent soil cohesion is well documented and many values of root additional cohesion are available in the literature for different plant species. However, less information is given about the spatial variation of soil reinforcement by roots at a slope scale and its influence on slope stability, in particular in forest areas.The goal of this paper is to describe the spatial variability of root additional cohesion on two monospecific 17-y-old stands of Robinia pseudoacacia and Platycladus orientalis grown on slopes in the semiarid Loess Plateau of China, and to analyze numerically the effect of this variability on slopes stability. For this purpose, vertical trenches were dug at different distance and directions around trees situated at three different slope locations, i.e. up-, mid- and down-slope. Grids with a 10. ×. 10. cm mesh were placed on vertical walls. Roots were counted within each grid cell and split according to their diameter class. Root area ratio (RAR) was estimated and compared among different positions around the trees and at three different locations along the slope. Roots tensile strength was determined with laboratory mechanical tests. RAR and root tensile strength were used as inputs in six different root reinforcement models to calculate root additional cohesion. A 2D finite element model of slope stability was developed and used to calculate the increase in factor of safety (FoS) due to root additional cohesion on rectilinear and terraced slopes.Results showed that both root tensile strength and Young's modulus of R. pseudoacacia was about two times higher than tensile strength of P. orientalis. RAR distribution had a strong relationship with local soil moisture content measured in July during the raining season, and was significantly different with regards to tree location on the slope. The six theoretical models used to estimate the root additional cohesion gave different vertical profiles of root reinforcement distribution according to the underlying hypothesis on how forces are transferred to the roots. Theoretical analyses of slope stability showed that terraced slopes were 20% more stable than rectilinear slopes, disregarding the differences in hydrological regimes between these two terrain morphologies. Numerical sensitivity analyses also showed that the FoS reached an asymptotic value when increasing root additional cohesion. Actual additional cohesions of the two studied sites corresponded to FoS that were already close to this asymptotic values. Consequently variations of these actual root cohesions would not much affect slope stability. However it was showed that more attention should be given to the reinforcement of the bottom part of the actual slopes, where roots have a larger positive impact on the FoS. © 2011 Elsevier B.V.

Mamoun C.M.,University of Mauritius | Nigel R.,Center Eau Terre Environnement | Rughooputh S.D.D.V.,University of Mauritius
Wetlands | Year: 2013

Past studies conducted on wetlands of Mauritius lead to the conclusion that half of the wetlands have been backfilled for touristic and housing development and that the ecological condition of the remaining wetlands is being seriously challenged by numerous threats, natural and anthropogenic. This research aimed to fill the information gap concerning wetland type and distribution. For this, using published maps and satellite imagery, wetlands were digitised resulting in 144 wetlands and categorised into 8 ecological units. Afterwards, a number of wetlands were ranked according to their environmental condition based on a series of Land Cover Indices (LCIs). These indices were derived by analysis of land cover types and slope gradient within a 50 m and a 950 m watershed-bounded buffer zone. Wetlands in forested areas were the least disturbed, with LCI of typically 0.30, but potentially threatened by sediment accumulation due to a high slope gradient (>20 %). Three wetlands in Mauritius are classified as Ramsar wetland. One of them, the Blue Bay Marine Park (BBMP) has moderately good condition (LCI = 0.55). The other one, the Rivulet Terre Rouge Estuary Bird Sanctuary (RTREBS) was among the most heavily impacted (LCI = 0.87) due to intensive urbanization. © 2013 Society of Wetland Scientists.

Dubreuil-Boisclair C.,Center Eau Terre Environnement | Gloaguen E.,Center Eau Terre Environnement | Bellefleur G.,Geological Survey of Canada | Marcotte D.,Ecole Polytechnique de Montréal
Marine and Petroleum Geology | Year: 2012

For the past decades, gas hydrate reservoirs have beneficiated from an increasing attention in the academic and industrial worlds. As a result, there is a growing need to develop specific and comprehensive gas hydrate reservoir characterization methods. This study explores the use of a stochastic Bayesian algorithm to integrate well-logs and 3D acoustic impedance in order to estimate gas hydrate grades (product of saturation and total porosity) over a representative volume of the Mallik gas hydrate field, located in the Mackenzie Delta, Northwest Territories of Canada. First, collocated log data from boreholes Mallik 5L-38 and 2L-38 are used to estimate the statistical relationship between acoustic impedance and gas hydrate grades. Second, conventional stochastic Bayesian simulation is applied to generate multiple gas hydrate grade 3D fields integrating log data and lateral variability of 3D acoustic impedance. These equiprobable scenarios permit to quantify the uncertainty over the estimation, and identify zones where this uncertainty is greater. Contrary to conventional stochastic reservoir modeling workflows, the proposed method allows integrating non Gaussian and non linear distributions. This permits to handle bimodal distributions without using complex stochastic transforms. The results present gas hydrate grade values that are in accordance with well-log data. The relatively low standard deviation calculated at each pixel using all realizations suggests that gas hydrate grades is well explained by acoustic impedance and log data. © 2012 Elsevier Ltd.

El-Alem A.,Center Eau Terre Environnement | Chokmani K.,Center Eau Terre Environnement | Laurion I.,Center Eau Terre Environnement | El-Adlouni S.E.,University of Moncton
Remote Sensing | Year: 2012

The occurrence and extent of intense harmful algal blooms (HABs) have increased in inland waters during recent decades. Standard monitor networks, based on infrequent sampling from a few fixed observation stations, are not providing enough information on the extent and intensity of the blooms. Remote sensing has great potential to provide the spatial and temporal coverage needed. Several sensors have been designed to study water properties (AVHRR, SeaBAM, and SeaWIFS), but most lack adequate spatial resolution for monitoring algal blooms in small and medium-sized lakes. Over the last decade, satellite data with 250-m spatial resolution have become available with MODIS. In the present study, three models inspired by published approaches (Kahru, Gitelson, and Floating Algae Index (FAI)) and a new approach named APPEL (APProach by ELimination) were adapted to the specific conditions of southern Quebec and used to estimate chlorophyll-a concentration (Chl-a) using MODIS data. Calibration and validation were provided from in situ Chl-a measured in four lakes over 9 years (2000-2008) and concurrent MODIS imagery. MODIS bands 3 to 7, originally at 500-m spatial resolution, were downscaled to 250 m. The APPEL, FAI, and Kahru models yielded satisfactory results and enabled estimation of Chl-a for heavy blooming conditions (Chl-a < 50 mg·m -3), with coefficients of determination reaching 0.95, 0.94, and 0.93, respectively. The model inspired from Gitelson did not provide good estimations compared to the others (R 2 = 0.77). However, the performance of all models decreased when Chl-a was below 50 mg·m -3. © 2012 by the authors.

Nigel R.,Center Eau Terre Environnement | Rughooputh S.D.D.V.,University of Mauritius
Soil Research | Year: 2012

Soil erosion by water is one of the most important natural resources management problems in the world. The damages it causes on-site are soil loss, breakdown of soil structure, and decline in organic matter content, nutrient content, fertility, and infiltration rate. Lands with the highest erosion risk on Mauritius Island are crop cultivations (sugarcane, tea, vegetables) on erosion-susceptible terrain (slopes >20% coupled with highly erodible soils). The locations of such lands on Mauritius were mapped during previous, qualitatively based regional-scale erosion studies. In order to propose soil conservation strategies, there is a need to apply a more quantitative approach to supplement the previous, qualitatively based studies. This paper reports an application of the Revised Universal Soil Loss Equation (RUSLE) within a geographical information system in order to estimate soil loss on the island, and particularly for the high-erosion areas. Results show that total soil loss on the island is estimated at 298259tyear-1, with soil loss from high-erosion areas summing 84780tyear-1 (28% of total soil loss). If all of the high-erosion areas were afforested, their soil loss would be reduced to 10264tyear-1, i.e. a reduction of 88% for the high-erosion areas and a reduction of 25% for the island. This study thus calls for soil and water conservation programs directed to these erosion-prone areas before the land degradation and environmental damage they are causing become irreversible. The methodological approach used in this work to quantitatively estimate soil loss from erosion-prone areas can be adopted in other countries as the basis for a nationwide erosion assessment in order to better inform environmental policy needs for soil and water conservation. © 2012 CSIRO.

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