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What role do lakes play in GHG emissions?

In Canada, a lake with a surface area of one square kilometre emits as much greenhouse gas (GHG) in a single day as a car making a round trip between Montreal and Vancouver. This figure is quite alarming, considering that the country has nearly one million lakes!

Lakes are a significant source of GHG emissions to the atmosphere, as they receive all the organic matter washed from the land, becoming a “brew” that emits mainly carbon dioxide (CO2) and methane (CH4).

This natural process has always existed and is not a problem in itself. However, scientists like those on the team of Yves Prairie, a professor and researcher in the Department of Biological Sciences at UQAM, would like to understand how lake GHG emissions are influenced by climate change and what the impact will be on the total GHG balance for Québec, Canada and other regions of the world.

In the summer, there is naturally very little gas exchange between the warm water layer that forms at the surface of a lake and the colder layer at the bottom. Climate change is causing this stratification to remain in place longer, with a likely impact on gas emissions. If this situation benefits methane-consuming bacteria, the lakes will emit less of this highly polluting gas. But it could also be beneficial to methane-producing bacteria… In other words, if Canada manages to reduce its anthropogenic emissions by 20% but its lakes release 20% more gas, the country will not reduce its carbon footprint.

Yves Prairie and his colleagues are therefore seeking to model the processes that control lake GHG emissions in order to better assess the role of lakes and to be able to drive global climate models. Together with Swedish collaborators, they have developed new GHG models from their data and are running them on the world’s five million lakes to estimate the current GHG production of these bodies of water and the fluctuations under climate projections. So far, they are able to explain observed CO2 variations. As for methane, they suspect that warmer temperatures will favor methane-producing bacteria more than methane-consuming bacteria, but this remains to be confirmed.