Combining in situ flux measurements and multi-temporal UAV LiDAR on a degrading palsa.

Palsa mires are elevated mounds of peat with a permanently frozen core found in areas of discontinuous permafrost. Peatlands in the subarctic, which is where these landforms are located, hold more than 30% of the stored global soil carbon, which is a disproportionate amount considering their extent. As permafrost thaws, as a result of the subarctic region warming approximately twice as fast as the global average, this carbon is released to the atmosphere in the form of CH₄ or CO₂.

The aim of this study is to measure methane emissions on a degrading palsa in the Vissátvuopmi palsa mire complex located in the northernmost part of Sweden, using carbon flux measurements. The 4 m tall palsa under study has been mapped with repeat UAV LiDAR data (five campaigns during one year) to characterize the intra-annual subsidence of the palsa in high spatial detail. Using the flux measurements and UAV LiDAR data, correlations will be investigated between methane fluxes and other factors such as topographic position, soil moisture and soil temperature, active layer depth and vegetation.  

The findings show some expected results with high emission of methane in areas where the palsa has fully collapsed, and low uptake in areas which have undergone the least amount of degradation. Surprisingly, there is low uptake to low emission in areas of the palsa which have recently degraded significantly. There is no significant correlation between fluxes and the other factors measured in connection to this study (soil moisture, soil temperature, active layer depth and type of vegetation). However, it is possible to detect in the data that, in general, the measurements with low or negative flux have a lower soil moisture percentage (>40-50%) while the measurements with higher fluxes have a soil moisture content above 50%. Using available geospatial data and field observations, an estimation of the current methane emissions from the palsa was made. From these calculations, in addition to the decay rate of the palsa (established in Olvmo et al. (2020)), future emissions will be estimated.