Annual follow-up of gross diffusive carbon dioxide and methane emissions from a boreal reservoir and two nearby lakes in Québec, Canada

Abstract. Surface water pCO₂ and pCH₄ measurements were taken in the boreal zone of Québec, Canada, from summer 2006 to summer 2008 in Eastmain 1 reservoir and two nearby lakes. The goal of this follow-up was to evaluate annual greenhouse gas (GHG) emissions, including spring emissions (N.B. gross emissions for reservoir), through flux calculations using the thin boundary layer model. Our measurements underscored the winter CO₂ accumulation due to ice cover and the importance of a reliable estimate of spring diffusive emissions as the ice breaks up. We clearly demonstrated that in our systems, diffusive CH₄ flux (in terms of CO₂ equivalent) were of minor importance in the GHG emissions (without CH₄ accumulation under ice), with diffusive CO₂ flux generally accounting for more than 95% of the annual diffusive flux. We also noted the extent of spring diffusive CO₂ emissions (23% to 52%) in the annual carbon budget.