Wildfires' intensity and frequency have increased across northern landscapes, disrupting carbon cycling and transport across terrestrial-aquatic ecosystems. However, it remains unclear how lake carbon dynamics respond to fires due to the lack of studies including both spatial and temporal gradients. We analyzed the concentration and distribution of C-species (DOC, DIC, POC, CO₂, CH₄,) in 56 lakes in burnt vs control catchments in 3 boreal regions of Quebec and Minnesota with a 3-year post-fire gradient. Overall, lakes were more similar within than among regions regardless of fire, but there were intra-regional fire effects. DOC increased in lakes in burnt watersheds, and surface water oxygen concentrations were typically lower in burnt vs control watersheds despite no significant effect on concentrations of CO₂ and CH₄. In addition, wildfires increase the contribution of DOC to whole-lake C budgets favouring reduction of water transparency and greater opportunity for in-situ carbon processing through mineralization. This lake C dynamic change through an increased quantity and proportion of DOC suggests a potential long-term fire mediated carbon export with a yet undetermined fate in boreal watersheds. Through the integration of various C species with different turnover rates and fates this study highlights a potential longer-term fire-effect on C cycling at the watershed scale with possible implication on global C cycling.

Primary Presenter: Mathilde Belair, Universite de Montreal (mathilde.belair@umontreal.ca)

Authors:

Mathilde Belair, Université de Montréal  (mathilde.belair@umontreal.ca)

Ian McCullough, Michigan State University  ()

Christopher T. Filstrup, University of Minnesota Duluth  ()

Jennifer A. Brentrup, Minnesota Pollution Control Agency  ()

Jean-Francois Lapierre, Université de Montréal  ()