WINTER AND HYPOLIMNETIC CO₂ DYNAMICS IN QUÉBEC LAKES: CONTRIBUTION TO THE ANNUAL CO₂ BUDGET, AND LINKS TO RESPIRATORY QUOTIENT AND SOURCES OF ORGANIC CARBON

Ducharme-Riel, V., Université du Québec à Montréal, Montreal, Canada (veronique.riel@hotmail.com),
del Giorgio, P. A., Université du Québec à Montréal, Montréal, Canada (del_giorgio.paul@uqam.ca),
Prairie, Y. , Université du Québec à Montréal, Montréal, Canada (prairie.yves@uqam.ca).

Here we compare the whole-lake accumulation of CO₂ during winter ice-cover, to that in the hypolimnion during summer stratification, in a wide range of lakes in temperate and boreal lakes in Québec, and we explore the relative importance of these two seasonal components to the annual lake CO₂ budget. We further assessed the coupling between O₂ and CO₂ dynamics, and used Keeling based on changes in ¹³C-DIC to assess potential sources of organic matter fuelling winter under-ice, and summer hypolimnetic biological CO₂ production. We show that winter CO₂ accumulation was remarkably similar across lakes, and on average larger than hypolimnetic CO₂ accumulation; together they accounted for on average over 30 % of the annual CO₂ budget in across lakes. There was a close coupling between O₂ and CO₂ dynamics, which suggests that much of this CO₂ accumulation is biologically-derived, with benthic processes accounting for over 60% of winter CO₂ fluxes. Interesting, Keeling plots show that the sources of OM fuelling this CO₂ accumulation are drastically different between winter under-ice and summer hypolimnia.

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