Abstract
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.
Highlights
The involvement of freshwater ecosystems in the global carbon budget has long been neglected because of their limited surface coverage on a worldwide scale, compared with forest or oceans
We present a comparison of gross diffusive emissions from Eastmain 1 reservoir and two nearby lakes to document the effect of anthropogenic reservoir creation on aquatic greenhouse gas (GHG) emissions
We did annual estimates of diffusive GHG emissions at Robert Bourassa reservoir (Quebec, Canada) with data collected in 2006 and we found higher potential spring emissions (22% of annual emissions) than those reported by Duchemin et al (2006) for shallow areas, whereas spring diffusive GHG flux amounted to only 7% of annual flux at Robert Bourassa reservoir
Summary
The involvement of freshwater ecosystems in the global carbon budget has long been neglected because of their limited surface coverage on a worldwide scale, compared with forest or oceans. It has been demonstrated that the loading of terrestrial dissolved organic carbon can contribute significantly to the energy pathways of lake ecosystems (Tranvik, 1992; Pace et al, 2004; Carpenter et al, 2005), sometimes leading to respiration rates exceeding primary production rates (Del Giorgio et al, 1997). This state, called ecosystem net heterotrophy, is believed to be largely responsible for the CO2 supersaturation observed in most of the world’s lakes (Cole et al, 1994; Del Giorgio et al, 1999; Duarte and Prairie, 2005). Lakes clearly appear to be sources of carbon emissions to the atmosphere
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