Deshmukh C.,CNRS Laboratory for Aerology |
Deshmukh C.,TERI University |
Serca D.,CNRS Laboratory for Aerology |
Delon C.,CNRS Laboratory for Aerology |
And 9 more authors.
Biogeosciences | Year: 2014
In the present study, we measured independently CH4 ebullition and diffusion in the footprint of an eddy covariance system (EC) measuring CH4 emissions in the Nam Theun 2 Reservoir, a recently impounded (2008) subtropical hydroelectric reservoir located in the Lao People's Democratic Republic (PDR), Southeast Asia. The EC fluxes were very consistent with the sum of the two terms measured independently (diffusive fluxes + ebullition Combining double low line EC fluxes), indicating that the EC system picked up both diffusive fluxes and ebullition from the reservoir. We showed a diurnal bimodal pattern of CH4 emissions anti-correlated with atmospheric pressure. During daytime, a large atmospheric pressure drop triggers CH4 ebullition (up to 100 mmol mg-2 d-1), whereas at night, a more moderate peak of CH4 emissions was recorded. As a consequence, fluxes during daytime were twice as high as during nighttime. Additionally, more than 4800 discrete measurements of CH4 ebullition were performed at a weekly/fortnightly frequency, covering water depths ranging from 0.4 to 16 m and various types of flooded ecosystems. Methane ebullition varies significantly seasonally and depends mostly on water level change during the warm dry season, whereas no relationship was observed during the cold dry season. On average, ebullition was 8.5 ± 10.5 mmol mg-2 d -1 and ranged from 0 to 201.7 mmol mg-2 d-1. An artificial neural network (ANN) model could explain up to 46% of seasonal variability of ebullition by considering total static pressure (the sum of hydrostatic and atmospheric pressure), variations in the total static pressure, and bottom temperature as controlling factors. This model allowed extrapolation of CH4 ebullition on the reservoir scale and performance of gap filling over four years. Our results clearly showed a very high seasonality: 50% of the yearly CH4 ebullition occurs within four months of the warm dry season. Overall, ebullition contributed 60-80% of total emissions from the surface of the reservoir (disregarding downstream emissions), suggesting that ebullition is a major pathway in young hydroelectric reservoirs in the tropics. © Author(s) 2014.
Tremblay A.,Hydro - Quebec |
Bastien J.,Environnement Illimite |
Strachan I.,McGill University |
Bonneville M.-C.,McGill University
International Journal on Hydropower and Dams | Year: 2010
Three methods to study CO2 and CH4 fluxes at Eastmain 1 reservoir, Canada, are presented. The methods include measuring gas partial pressures with gas chromatography and infrared instruments during field and with automated systems, measuring direct fluxes with floating chambers, and measuring CO2 concentration in the air originating from a large upwind area using the eddy covariance technique. The results show that greenhouse gases can be emitted from hydroelectric reservoirs by diffusion at the surface of the reservoir, ebullition in the reservoir, and degassing in the white waters downstream of the reservoir. The methods showed pCO2 ranging from 575 to 5004 μatm, corresponding to CO2 fluxes ranging from 291 to 12,872 mg CO2 m-2 d-1 for the stations sampled in the Eastmain 1 region from 2003 to 2008.
Hardy F.,Poly Geo inc. 624 Notre Dame |
Bariteau L.,Poly Geo inc. 624 Notre Dame |
Lorrain S.,Environnement Illimite |
Theriault I.,Hydro - Quebec |
And 3 more authors.
Catena | Year: 2010
A four-reservoir hydroelectric complex which is projected on the Romaine River, in eastern Québec, Canada, will likely lead to the complete settling of the sand-size bed load of the river. In order to characterise the present river bed load sources, sediment transport and sedimentary connectivity, a study was conducted to document the compositional continuum of the lower 300 km portion of the river. Bed load samples were collected during the late summer low water period and ICP-MS geochemical analyses of the light and heavy mineral portions were conducted. Principal component analysis of the results successfully identified a series of distinctive geochemical domains. Multivariate Euclidean distance coefficients were also calculated between consecutive samples along the river revealing major bed load compositional breaks. These results indicate a longitudinal fractionation of the bed load along the 300 km course of the river. This is further supported by the sedimentary budget calculated from the annual sedimentary input derived from erosion rates of the river banks, from sediment bed load measurements at three gauging stations and from calculated bed load transport capacity at these three locations. It appears that significant sediment accommodation space is available on the upper course (250 km) of the Romaine River, in spite of the fact that this river has drained highly sediment-laden meltwaters from the receding Laurentide Ice Sheet, some 10 ka ago. This accommodation space leads to the renewal of the bed load due to recurrent partial to complete sedimentation. The major part of the bed load reaching the Romaine River mouth originates from the lower 50 km of the river course. © 2010 Elsevier B.V. All rights reserved.
Verdon R.,Hydro - Quebec |
Guay J.-C.,Hydro - Quebec |
La Haye M.,Environnement Illimite |
Simoneau M.,Environnement Illimite |
And 3 more authors.
Journal of Applied Ichthyology | Year: 2013
The Rupert River is one of the largest tributaries on the east coast of James Bay. Lake sturgeon (Acipenser fulvescens) is present all along the main stem where several spawning grounds have been located, four of which are major spawning grounds that have been studied at km 216, 281, 290 and 362. The total number of drifting larvae was estimated with drift nets set along transverse transects at km 212, 276, and km 287 from 2007 to 2009, and at km 361 in 2008 and 2009, using a new technique, namely, a Doppler current meter to measure water velocity within transect sub-sections corresponding to Voronoï polygons. There was a substantial, persistent difference in the number of larvae produced by the four main spawning areas. On average, the most productive site (km 276) produced over five times more larvae than the least productive site (km 361). Average estimated numbers were 41,194 at km 212, 176,840 at km 276, 106,212 at km 287, and 30,642 at km 361. Temporal variations were of much less amplitude than spatial differences. Between 2007 and 2009, interannual variations were not significant, except at km 212, despite differences in river flow during incubation and larval drift. The number of gravid females and the quality of spawning grounds would likely be the main factors influencing the total number of larvae. Vertical distribution of larvae is variable between sites and years, and shows a slight tendency for larvae to be more surface oriented. Higher flow near the surface would partly explain larger surface drifting of larvae. Transverse distribution is uneven and often associated with the location of the spawning grounds and the river flow. Given the uneven vertical and transverse distribution of larvae, an effective sampling strategy should cover the complete water column and full river width. Where depth exceeds 3 m, at least two stacked nets are recommended. In large rivers, filtering close to 1% of total river flow should result in acceptable confidence intervals, allowing a good comparison of the number of larvae in space and time. © 2012 Blackwell Verlag GmbH.
Demarty M.,Environnement Illimite |
Bastien J.,Environnement Illimite
Energy Policy | Year: 2011
Greenhouse gas (GHG) emissions from reservoirs have been under the microscope for more a decade now. In particular, the high CH 4 emissions reported in warm systems have tarnished the green credentials of hydroelectricity in terms of GHG emissions. Reliable estimates of CH 4 emissions are crucial, since CH 4 has a greenhouse warming potential of 25 and because, unlike CO 2, CH 4 emissions should be counted for the entire life cycle of a reservoir. Up to now, the highest CH 4 emissions from reservoirs have been measured in warm latitudes, thus adding an argument against the use of hydroelectricity in these regions. However, to our knowledge, GHG emissions have been measured for only 18 of the 741 large dams (>10MW, according to the ICOLD register) listed in the tropics. This article reviews the limited scientific information available and concludes that, at this time, no global position can be taken regarding the importance and extent of GHG emissions in warm latitudes. © 2011 Elsevier Ltd.