Hydro-Québec is the largest electric power company in Canada with more than 35 000 MW installed for an annual generation of around 189 TWh. Hydro-Québec owns and operates over 57 powerhouses such as Eastmain-1 that was commissioned in 2005. The growing concern regarding the long-term contribution of freshwater reservoirs to atmospheric greenhouse gases (GHG), led Hydro-Québec, to study net GHG emissions from Eastmain-1 reservoir, which are the emissions related to the creation of a reservoir minus those that would have been emitted or absorbed by the natural systems over a 100-year period. This large study is realized in collaboration with Environnement IIlimité Inc., University du Quebec in Montreal and McGill University.Measurement of GHG fluxes were done with the used of a traditional technique, the floating chambers that measures GHG fluxes at the water-air interface and a new approach using automated systems measuring partial pressure of gas in the water column. Follow up of the CO2 and CH4 fluxes at EM-1 reservoir showed a rapid increase in both CO2 and CH4 emissions the first year after flooding and a rapid return to natural aquatic ecosystems values within 2 and 3 year for CH4 and CO2, respectively. Automated system and floating chambers show similar annual GHG mass balance. Overall GHG emissions from Eastmain-1 reservoir are very low in comparison to thermal power plant of the same capacity.
Greenhouse gas (GHG) emissions from hydroelectric dams are often portrayed as nonexistent by the hydropower industry and have been largely ignored in global comparisons of different sources of electricity. However, the life cycle assessment (LCA)of any hydroelectric plant shows that GHG emissions occur at different phases of the power plant's life. This work examines the role of decommissioning hydroelectric dams in greenhouse gas emissions. Accumulated sediments in reservoirs contain noticeable levels of carbon, which may be released to the atmosphere upon decommissioning of the dam. The rate of sediment accumulation and the sediment volume for six of the ten largest United States hydroelectric power plants is surveyed. The amount of sediments and the respective carbon content at the moment of dam decommissioning (100 years after construction) was estimated. The released carbon is partitioned into CO2 and CH4 emissions and converted toCO2 equivalent emissions using the global warming potential (GWP) method. The global warming effect (GWE) due to dam decommissioning is normalized to the total electricityproduced over the lifetime of each power plant. The estimated GWE of the power plants range from 128-380 g of CO2eq./kWh when 11% of the total available sediment organic carbon (SOC) is mineralized and between 35 and 104 g of CO2eq./kWh when 3% of the total SOC is mineralized. Though these values are below emission factors for coal power plants (890 g of CO2eq./kWh), the amount of greenhouse gases emitted by the sediments upon dam decommissioning is a notable amount that should not be ignored and must be taken into account when considering construction and relicensing of hydroelectric dams
Estimates suggest that, per unit of energy produced, greenhouse-gas flux to the atmosphere from some hydroelectric reservoirs may be significant compared to greenhouse-gas emission by fossil-fuelled electricity generation. In Canada, there are about 20,000 km^2 of peatland and upland areas covered by hydroelectric reservoirs with over 11,000 km^2 more planned. We hypothesize that development of hydroelectric reservoirs may increase the flux of CH4 and CO2 to the atmosphere. Our hypothesis is based on past studies which show that both upland forests and peatlands are sites of intense microbial decomposition and greenhouse-gas production when they become covered in water. Depending on the extent of flooding and other physical, chemical and biological features, some reservoirs may be significant emitters of greenhouse gases.
American Rivers produced abstract