Spatiotemporal Analysis of Thermokarst-Related Open Water Dynamics and Active Layer Change in the Stordalen Mire

Sammanfattning

Fennoscandian permafrost peatlands and palsa mires have exhibited pronounced thawing over recent decades, resulting in increased active layer thickness (ALT) and thermokarst formation. Consequently, open water areas have expanded in the well-studied palsa mire Stordalen, located in northernmost Sweden. However, long-term quantifications of open water dynamics remain limited and the relationship between ALT and open water change has received limited attention. Therefore, this thesis investigates spatiotemporal open water dynamics and their relationship to ALT change. Open water areas were identified through manual delineation of historical aerial imagery (1959–2018), combined with Random Forest classification of recent high-resolution imagery (2017–2024). In-situ measurements of ALT, spanning 2010-2018, were incorporated into the analysis. Open water extent increased by 255% in 1959–2018. The number of ponds increased by 429%, although the trend was not linear and therefore not statistically significant. The contemporary analysis showed pronounced interannual variability in both open water extent and pond number. ALT increased significantly between 2010 and 2018, but no significant local relationship between ALT and open water change was found. These findings suggest that thermokarst systems in thawing palsa mires are highly dynamic and that ALT alone does not control local open water development, highlighting the need for continued research of the hydrological processes in thermokarst evolution.