Diffusive CO2 Flux at the Air-Water Interface of the Robert-Bourassa Hydroelectric Reservoir in Northern Québec : Isotopic Approach (13C)

Hydroelectric reservoirs and lakes in boreal Québec produce greenhouse gases (GHG) mainly in the form of CO

2

. No method exists, however, which can directly measure the flux of CO

2

across the air-water interface and the methods that are currently used are only representative of a small surface area and a specific time period. The objective of the current study is to improve and validate an isotopic approach to estimate the annual CO

2

flux across the air-water interface. The model requires the calibration of isotopic fluxes into and out of the interface. When applied to the Robert- Bourassa hydroelectric reservoir in boreal Québec, this model estimated an average CO

2

diffusive flux across the air-water interface of 225±51 mg CO

2

·m

−2

·d

−1

in the summer of 2000 and of 446±93 mg CO

2

·m

−2

·d

−1

in the summer of 2001. These average fluxes are representative of the whole icefree period.