Temporal assessment of cumulative impacts from interacting disturbances of wildfires and lake-level changes on a small lake in the Western Canadian Arctic

We analysed long-term ecosystem change in a small lake in the Tuktoyaktuk Coastlands (Northwest Territories, Canada). Lake 2B (unofficial name) has a history of polycyclic thaw slumping, associated with oligotrophic, clearwater conditions in this region. In 1968 Lake 2B was impacted by a wildfire that resulted in eutrophication, inferred from a rapid increase in the meso-eutrophic diatom Cyclostephanos in a sediment core. Eutrophic conditions were confirmed by water sampling in 2007 and 2017. Analysis of remote-sensing data revealed that Lake 2B experienced catastrophic drainage in 2012, likely in response to an extreme summer rainfall event. Field sampling confirmed that the lake re-filled between 2017 and 2023, with the re-filling resulting in re-oligotrophication. However, subfossil diatom assemblages showed that Cyclostephanos remained dominant. This contrasts with many temperate lakes, where recovery from eutrophication has been effectively tracked using diatom assemblages. We propose the lake experienced a hysteresis where exposure to an earlier disturbance (wildfire) influenced ecological responses to subsequent disturbance (lake drainage and re-filling). Overall, Lake 2B provides an interesting case study for understanding how interacting climate-related disturbances influence trajectories of Arctic lake ecosystem change, though it remains unclear if other lakes would respond similarly to past wildfires, lake drainage, and re-filling.