The net carbon footprint of a newly created boreal hydroelectric reservoir

We present here the first comprehensive assessment of the carbon (C) footprint associated with the creation of a boreal hydroelectric reservoir (Eastmain‐1 in northern Québec, Canada). This is the result of a large‐scale, interdisciplinary study that spanned over a 7‐years period (2003–2009), where we quantified the major C gas (CO 2 and CH 4 ) sources and sinks of the terrestrial and aquatic components of the pre‐flood landscape, and also for the reservoir following the impoundment in 2006. The pre‐flood landscape was roughly neutral in terms of C, and the balance between pre‐ and post‐flood C sources/sinks indicates that the reservoir was initially (first year post‐flood in 2006) a large net source of CO 2 (2270 mg C m −2 d −1 ) but a much smaller source of CH 4 (0.2 mg C m −2 d −1 ). While net CO 2 emissions declined steeply in subsequent years (down to 835 mg C m −2 d −1 in 2009), net CH 4 emissions remained constant or increased slightly relative to pre‐flood emissions. Our results also suggest that the reservoir will continue to emit carbon gas over the long‐term at rates exceeding the carbon footprint of the pre‐flood landscape, although the sources of C supporting these emissions have yet to be determined. Extrapolation of these empirical trends over the projected life span (100 years) of the reservoir yields integrated long‐term net C emissions per energy generation well below the range of the natural‐gas combined‐cycle, which is considered the current industry standard.