CO2 and CH4 diffusive and degassing emissions from 2003 to 2009 at Eastmain 1 hydroelectric reservoir, Québec, Canada

Gross aquatic carbon dioxide (CO 2 ) and methane (CH 4 ) emissions were measured before and after impoundment of Eastmain 1 (EM1) reservoir. Reservoir diffusive emissions were (1) measured in situ during field campaigns using floating a chamber, and (2) calculated from gas concentration measurements using the Thin Boundary Layer equation. Reservoir diffusive (surface) emissions and downstream degassing emissions were also estimated from continuous measurements of gas concentration at the electricity generating station. Diffusive CO 2 and CH 4 emissions from EM1 reservoir were highest during the first year after impoundment (2006) and decreased over the following years. Diffusive CO 2 emissions from the reservoir surface and downstream degassing emissions were higher in spring following the winter CO 2 buildup under the ice cover, whereas reservoir diffusive CH 4 emissions and downstream degassing emissions were higher during summer, when water temperature was at its maximum. Most of the reservoir emissions occur in the form of CO 2 (>98%, reservoir surface and downstream emissions), with CH 4 emissions (diffusive, degassing) representing <2% of total annual CO 2 equivalent emissions.