[en] Organic matter decomposition in permafrost soils depends on factors such as soil pH, temperature, and redox conditions. Over lowland permafrost soils, these conditions are shaped by microtopography, which evolves with physical degradation, i.e., lowland thermokarst development. A dynamic quantification of lowland thermokarst development-still poorly constrained-is therefore a critical prerequisite for predictive models of permafrost carbon balance in these areas. Here we provide such a quantification, updated for the Stordalen mire in Abisko, Sweden (68°21 20 N, 19°02 38 E), which displays a gradient from well-drained stable palsas to inundated fens, which have undergone ground subsidence. We produced RGB orthomosaics and digital surface models from very high resolution (10 cm) unoccupied aircraft system (UAS) photogrammetry as well as a spatially continuous map of soil electrical conductivity (EC) based on electromagnetic induction (EMI) measurements. We classified the land cover following the degradation gradient using a support vector machine algorithm and derived palsa loss rates. Our findings confirm that topography is a key variable for monitoring palsa loss, nearly doubling the overall accuracy of the classification, while slope enabled the identification of early-stage degradation. We show a clear acceleration of degradation for the period 2019-2021, with a decrease in palsa area of 3.3-3.6 % a −1 (% reduction per year relative to the initial palsa areal extent) compared to previous estimates of ∼ 0.3 % a −1 (1970-2000) and ∼ 0.1 % a −1 (2000-2014). EMI data show that this degradation leads to an increase in soil moisture, which in turn likely decreases organic carbon geochemical stability and potentially increases methane emissions. With a palsa loss of 3.3-3.6 % a −1 , we estimate accordingly that surface degradation at Stordalen might lead to a pool of 12 × 10 3 kg of organic carbon exposed annually within the topsoil (23 cm depth), of which ∼ 25 % is mineral-interacting organic carbon. These results demonstrate that UAS monitoring can robustly quantify rapid thermokarst development that coarser methods miss, and provide a transferable framework for tracking permafrost degradation rates at other lowland sites.
Thomas, Maxime ; Earth and Life Institute, Université catholique de Louvain, Louvain-la-Neuve, Belgium
Moenaert, Thomas; Earth and Life Institute, Université catholique de Louvain, Louvain-la-Neuve, Belgium
Radoux, Julien; Earth and Life Institute, Université catholique de Louvain, Louvain-la-Neuve, Belgium
Delhez, Baptiste ; Earth and Life Institute, Université catholique de Louvain, Louvain-la-Neuve, Belgium
du Bois d'Aische, Eléonore ; Université de Liège - ULiège > Sphères ; Université de Liège - ULiège > Faculté des Sciences > Doct. scienc. (géographie) ; Université de Liège - ULiège > Faculté des Sciences > Form. doct. sc. (géog. - paysage) ; Earth and Life Institute, Université catholique de Louvain, Louvain-la-Neuve, Belgium
Villani, Maëlle ; Earth and Life Institute, Université catholique de Louvain, Louvain-la-Neuve, Belgium
Hirst, Catherine; Earth and Life Institute, Université catholique de Louvain, Louvain-la-Neuve, Belgium ; Department of Earth Sciences, Durham University, Durham, UK
Lundin, Erik ; Abisko Scientific Research Station, Swedish Polar Research Secretariat, Abisko, Sweden
Jonard, François ; Université de Liège - ULiège > Sphères ; Université de Liège - ULiège > Département de géographie > Earth Observation and Ecosystem Modelling (EOSystM Lab) ; Université de Liège - ULiège > Département de géographie
Lambot, Sébastien; Earth and Life Institute, Université catholique de Louvain, Louvain-la-Neuve, Belgium
Van Oost, Kristof; Earth and Life Institute, Université catholique de Louvain, Louvain-la-Neuve, Belgium
Vanacker, Veerle ; Earth and Life Institute, Université catholique de Louvain, Louvain-la-Neuve, Belgium ; Soil Geography and Landscape Group, Wageningen University & Research, Wageningen, the Netherlands
Siewert, Matthias ; Department of Ecology and Environmental Science, Umeå University, Umeå, Sweden
Mörth, Carl-Magnus; Department of Geological Sciences, Stockholm University, Stockholm, Sweden
Palace, Michael; Department of Earth Sciences and Institute for the Study of Earth, Oceans and Space, University of New Hampshire, Durham, USA ; Earth Systems Research Center, Institute for the Study of Earth, Oceans and Space, University of New Hampshire, Durham, USA
Varner, Ruth ; Department of Geological Sciences, Stockholm University, Stockholm, Sweden ; Department of Earth Sciences and Institute for the Study of Earth, Oceans and Space, University of New Hampshire, Durham, USA ; Earth Systems Research Center, Institute for the Study of Earth, Oceans and Space, University of New Hampshire, Durham, USA
Sullivan, Franklin; Earth Systems Research Center, Institute for the Study of Earth, Oceans and Space, University of New Hampshire, Durham, USA
Herrick, Christina ; Earth Systems Research Center, Institute for the Study of Earth, Oceans and Space, University of New Hampshire, Durham, USA
Opfergelt, Sophie ; Earth and Life Institute, Université catholique de Louvain, Louvain-la-Neuve, Belgium
ERC - European Research Council F.R.S.-FNRS - Fonds de la Recherche Scientifique NSF - National Science Foundation NASA - National Aeronautics and Space Administration DOE - United States. Department of Energy
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