PhD defence: Mathilde Jammet

Mathilde Jammet defends her PhD thesis: 

Fluxes of methane and carbon dioxide from a subarctic lake
Seasonality and significance within the landscape 

Supervisor
Associate Professor Thomas Friborg, IGN 

Assessment Committee
Professor Bo Elberling, IGN (chair)
Professor Anna Rutgersson, Uppsala Universitet
Senior Research Scientist Annalea Lohila, Finish meteorological Institute

After the PhD defence there will be a reception in Rød stue, Øster Voldgade 10, Area 6, First floor – everybody is welcome.

Summary
A potential feedback of natural Arctic and subarctic ecosystems to ongoing climate warming is a shift in their carbon emissions. Key uncertainties in the magnitude of these changes include the role of lakes and the role of non-summer seasons in the landscape’s carbon budget. These were addressed in this PhD project by measuring nearly continuously surface-atmosphere exchange of methane (CH₄) and carbon dioxide (CO₂) in a lake and in an adjacent wetland during 2.5 years. Measurements were conducted with the eddy covariance method in a thawing subarctic peatland complex. It was found that the ice-melt season can be the primary carbon-emitting period for shallow, seasonally ice-covered lakes, due to the rapid release of gases that were stored under ice during winter.

The non-negligible contribution of the winter season for annual carbon emissions was demonstrated for all ecosystems under study. The lake was a major source of carbon in the spring season; annual emissions partially compensated the sink function of the wetland with respect to the atmosphere. Drivers of short-term variability in lake emissions were explored for all seasons, highlighting for example the predominance of CH₄ ebullition in summer. Furthermore, the thesis discusses the methodological challenges met when using the eddy covariance method in lake ecosystems.

The main findings of this thesis help defining the role of lake ecosystems within the carbon budgets of subarctic landscapes.

The thesis is available from the PhD administration office 04.1.417