The net terrestrial-aquatic carbon and GHG balance of boreal watersheds in a changing climate

The carbon dynamics of terrestrial and aquatic ecosystems are tightly coupled but play opposite roles in the exchange of carbon with the atmosphere. While forests and wetlands are generally sinks for atmospheric carbon dioxide, lakes, streams and rivers are most often significant sources. We integrated these terrestrial and aquatic components of the landscape in an analysis of >100 unperturbed catchments from Quebec's mid-boreal région, which shows that the latter are largely carbon-neutral with respect to the atmosphere (± 5 g C m-2 yr-1). The sink-source balance, however, varies among individual watersheds, to a large extent driven by the local magnitude of aquatic emissions. In a changing climate, we can expect these aquatic emissions to increase, in particular those associated to methane, resulting in an overall shift towards a negative net GHG balance of this boreal region. Patterns of carbon dynamics in both terrestrial and aquatic ecosystems along a latitudinal gradient will be used to provide constraints on the magnitude of the anticipated shifts.