Comparing atmospheric CO2 and CH4 exchange from a natural lake and a cascade reservoir in a boreal watershed across a seasonal cycle

Canada’s boreal landscapes are a globally important carbon sink. However, the majority of Canada’s hydroelectricity infrastructure is located in boreal landscapes and flooding disturbs their carbon cycle. Aspects of the aquatic boreal carbon cycle are uncertain and data on year-round, landscape-scale water-atmosphere carbon exchange are rare, limiting our understanding of hydroelectriy’s carbon budget impact. Here, we present CO₂ and CH₄ eddy flux data from the boreal La Romaine watershed in Québec, Canada. Parts of La Romaine were impounded for hydroelectricity starting in 2014. Since 2022, we have measured carbon fluxes at both the watershed’s oldest reservoir and a natural lake in the watershed. We estimated both water bodies’ atmospheric carbon flux and contrasted the fluxes’ drivers over the seasonal cycle by analyzing them in relation to atmospheric and hydrological measurements and with a biogeochemical model. We found that both water bodies were CO₂ sources, with the reservoir being a larger source. We observed a diel CO₂ flux cycle at both sites, indicative of algal photosynthesis or shoreline contamination and use a footprint model to assess this. The lake appeared to have near 0 CH₄ emissions while the reservoir was a small but significant CH₄ source. This may be related to pre-flood biomass and dissolved oxygen. Stratification and ice dynamics also appeared to play an important role in structuring emissions over the year. Our study contributes to our understanding of the boreal aquatic carbon cycle and will help constrain the carbon effect of hydroelectricity.

Primary Presenter: Sajjan Heerah, Dalhousie University (sajjanh2@gmail.com)

Authors:

Sajjan Heerah, Dalhousie University  (sajjan@dal.ca)

Antoine Thiboult, Université Laval  (antoine.thiboult@gci.ulaval.ca)

Deirdre Spearns, Dalhousie University  (dr691222@dal.ca)

Jean-Francois Lapierre, Université du Québec à Montréal  (jfrancoislapierre@gmail.com)

Julie Talbot, Université de Montréal  (j.talbot@umontreal.ca)

Daniel Nadeau, Université Laval  (Daniel.nadeau@gci.ulaval.ca)

Manuel Helbig, Dalhousie University  (manuel.helbig@dal.ca)