Monitoring greenhouse gas emissions from hydroelectric reservoirs in northern Quebec, Canada


Courtesy of PP Systems

Surface waters of natural freshwater bodies are capable of releasing far more carbon into the atmosphere than they absorb (Cole et al. 1994). Artificial reservoirs are also known to have environmental impacts which include greenhouse gas (GHG) emissions (Rosenberg et al. 1997, Fearnside et al. 2004, Tremblay et al. 2005). Therefore the inclusion of hydroelectric facilities as part of an overall strategy to produce clean energy requires quantification of GHGs associated with their construction. Vegetation submerged by impoundment of reservoirs ceases to function as a sink for atmospheric CO2 and undergoes microbial decomposition, releasing both CO2 and methane (CH4). Reservoirs above flooded peatlands in boreal regions may release more GHGs through decomposition than reservoirs created where upland boreal forests once stood (St. Louis et al. 2000), but other factors such as climate, reservoir age, and roughness of surface waters influence emissions as well.

A Canadian research team from Environnement Illimité, Inc., Université du Québec à Montréal (UQAM), McGill University, and Hydro- Québec are attempting to answer these and other important questions in northern Québec Province as part of the Eastmain Reservoir (EM-1) Project (Fig. 1). The reservoir under study encompasses 603 km2, 14% of which is now submerged peatland. Due to the difficulty of obtaining accurate measurements in aquatic environments, researchers are relying on two separate methods to compare results (Duchemin et al. 1999).

One method employed floating static chambers (Fig. 2) that are sampled directly using the CIRAS-SC (Fig. 3) to determine changes in CO2 concentrations at the air-water interface, monitored over 7 minute periods. The slope of the concentration over time represents the GHG flux. “Direct” fluxes are compared to theoretical CO2 fluxes between the surface water and atmosphere calculated by the thin boundary layer (TBL) method, for which the researchers used the EGM-4 (Fig. 4) to quantify the partial pressure of dissolved CO2 (pCO2). Essentially, TBL CO2 flux is the difference between CO2 concentration of water and the atmosphere, as influenced by air and water temperatures and wind speed over the water’s surface.

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