The Hudson Bay Lowlands peatland complex in Canada, the world’s second-largest peatland complex, is experiencing the impacts of climate change, potentially threatening its carbon sink capacity; however, the direction and magnitude of recent changes are uncertain, particularly in response to ongoing permafrost thaw, climate change, and isostatic rebound. In this project, we aim to document the vegetation changes and carbon (C) storage dynamics, in both the long- (millennial) and short-term (decadal to centennial), of polygonal permafrost peatlands in Wapusk National Park (WNP), located on the northwestern coast of Hudson Bay.
First, we aim to estimate the total C stored in peatlands in WNP and study the Holocene development history of polygonal permafrost peatlands. During 2023–2024, we collected twenty complete peat cores across the different land cover types and ecoregions within WNP. The twenty peat cores will be dated with radiocarbon (14C) and analyzed for total organic C. The peat cores collected from permafrost peat plateaus will also be examined for paleoecological and palaeoclimatological reconstructions, providing insights into major shifts in plant communities, climate, and permafrost dynamics during the Holocene. Preliminary results show that in WNP, peatland initiation and C accumulation connect to undergoing isostatic rebound. Peat accumulation began ca. 5705 cal. BP in the forest-tundra region and 2390 cal. BP in the coastal fen ecoregion. Permafrost peat plateaus store approximately 80.7 kg C m-2, with an average long-term apparent rate of carbon accumulation (LORCA) of 26.1 g C m-2 yr-1. At several sites, spruce and larch forests preceded contemporary, lichen-dominated peat plateaus.
Second, we will explore why the numerous ponds within the permafrost peatlands are now being infilled by Sphagnum mosses, the most important genus for storing C as peat, and whether this is linked to recent permafrost thaw. Twenty surface peat monoliths were collected along transects at the edges of seven ponds and will be dated with coupled 14C and lead-210 (210Pb) age-depth modeling and analyzed for total organic C, plant macrofossils, and diatom communities. Preliminary results from plant macrofossil analyses indicate infilling and a subsequent increase in Sphagnum cover over fen vegetation rather than thawing-induced subsidence of permafrost peat plateaus. However, this may differ between ecoregions (forest-tundra vs. subarctic peat plateau region), and the timing of the transitions from moss-sedge to Sphagnum peat will be verified with age-depth modeling and remote sensing techniques. These early results show that vegetation changes along the pond edges can significantly affect peatland C accumulation.
How to cite: Kolari, T. H. M., Bouchard, F., Cassidy, A., Collingwood, A., Cosyn Wexsteen, L., Duffe, J., Ferrant, S., Gandois, L., Sanderson, N. K., and Garneau, M.: Holocene development and recent vegetation and carbon storage dynamics in polygonal permafrost peatlands of the Hudson Bay Lowlands, Canada, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12881, https://doi.org/10.5194/egusphere-egu25-12881, 2025.
The response of greenhouse gas fluxes from the circum-Arctic tundra to rapidly rising temperatures is one of the deep uncertainties in climate change research. Numerous studies have substantially increased our understanding on the production of greenhouse gases from thawing permafrost. However, we do not know how fast and to which extent fresh organic matter (OM) from decaying plant litter, the amounts of which are increasing in warming permafrost landscapes, may be stabilized in thawing permafrost.
To investigate the stabilization of fresh plant litter in thawing permafrost, we incubated permafrost samples from two Siberian islands for nine years with 13C-labelled plant litter under oxic and anoxic conditions. Within this experiment, we quantified CO2 and CH4 formation from two carbon sources: soil organic carbon (SOC) and litter carbon (litter-C). These data were used to calibrate a two-pool carbon decomposition model for determining the mean residence times (MRT) of the labile and stable carbon pools of SOC and litter-C. At the end of the incubation, we fractionated the remaining OM into the dissolved, the particulate and the mineral associated SOC and litter-C.
Roughly halve of added litter-C were mineralised to CO2 and CH4 after the nine years. Most of the SOC and of the litter-C were bound to the mineral fraction. However, the final litter-C mineralisation rates were 10-fold higher than those of SOC, indicating that the mineral associated carbon fraction contains OM of different decomposability. The median MRT of the stable litter-C pool was 18yr (oxic) and 52yr (anoxic), indicating a substantial stabilization of litter-C in thawing permafrost. However, the MRT of the stable permafrost SOC pool was one order of magnitude higher, demonstrating that permafrost OM is dominated by relatively stable OM. Our data shows that carbon from fresh plant litter is preferentially bound to pre-existing SOC in the mineral fraction and that this carbon still has a relatively high decomposability. Furthermore, we did not find evidence that the particulate OM is more labile than the mineral associated OM, or that the particulate OM fraction may be used as a proxy for a more decomposable carbon pool in thawing permafrost.
How to cite: Knoblauch, C., Voigt, C., and Beer, C.: Stabilization of fresh organic matter from recent plant litter in thawing permafrost , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4430, https://doi.org/10.5194/egusphere-egu25-4430, 2025.
Soil organic matter (SOM) is a highly heterogeneous component of soils and its composition differs strongly between sites, depending on the specific environmental conditions. Thawing of permafrost leads to the exposure of large amounts of SOM to decomposition, resulting in the release of greenhouse gases. Moreover, SOM might be mobilized as dissolved organic matter (DOM), possibly contributing to losses of carbon from soils. Detailed knowledge of SOM composition is key for understanding mineralisation processes and for the quantification of greenhouse gas emissions from thawing permafrost soils of different moisture, thaw depth, parent material and slope position.
We sampled permafrost soils along two transects on Disko Island, West Greenland, to characterize SOM from soils with different characteristics. Installation of suction cups allowed pore water sampling to determine the amount and composition of DOM. We measured emissions of CO2 and CH4 with a manual chamber system to quantify greenhouse gas fluxes at the different sites. To determine the degree of SOM decomposition and the potential impact of site characteristics on greenhouse gas emissions and SOM leaching, we fractionated SOM and subsequently analysed lignin components, amino sugars, and stable isotopes (δ13C and δ15N). Molecular microbial analyses were carried out to understand the underlying biological processes that control SOM cycling and greenhouse gas production.
Lignin components and derived molecular ratios matched with the recent vegetation. Sites are characterized by woody angiosperms in the well aerated and drained soils at the top of the slopes and by herbaceous plants in the wetland area at the lower end of the transects. The data indicated weak decomposition at the wet sites and stronger decomposition at the dry sites, which correlated with the proportion of particulate OM within the total SOM. Stable isotopes showed according patterns, becoming more positive with depth within the soil profile but becoming more negative along the transects. Leaching of DOM showed a more complex pattern with the lowest C contents in the wettest areas and the highest C contents in the intermediate slope positions but increasing C contents within the soil profiles. Only the wettest sites emitted CH4, while the drier locations were neutral in terms of CH4 or acted as CH4 sinks. We observed decreasing CO2 emissions along the transects during the day, with the driest sites being sources of CO2. The observations of CH4 fluxes were supported by higher abundances of methanogenic microorganisms in the wetter areas.
The results underline the susceptibility of SOM to decomposition in thawing permafrost. While topsoils and litter layers contain larger amounts of SOM than subsoils, results suggest that C is transported downwards along the soil profile with infiltrating water, possibly buffering decomposition. DOM appears to be transported down the hillslopes until it is either drained into waterbodies or emitted as CH4. Concerning scenarios of soil moisture changes, and daily and seasonal variations in CO2 uptake, the observed soils might therefore turn from C sinks to sources. However, the extend of this C-relocation by lateral DOM transport has not yet been quantified and needs further observation.
How to cite: Peplau, T., Liebmann, P., Laes, L., Voigt, C., Knoblauch, C., Liebner, S., Bruhn, C., and Guggenberger, G.: Origin and transformation of soil organic matter in permafrost soils, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14970, https://doi.org/10.5194/egusphere-egu25-14970, 2025.
With thawing, permafrost soils can shift from dry, oxic conditions to wetlands, driving significant changes in soil biogeochemistry and plant community composition, ultimately altering climate-relevant greenhouse gas (GHG) dynamics. Graminoid species, such as Carex spp. and Eriophorum spp., thrive in anoxic soils, exhibit high primary productivity, release substantial amounts of organic root exudates fueling CO2 and CH4 emissions, and possess adaptive traits for anoxia. Among these traits is the formation of aerenchyma tissues, which enable oxygen release into the rhizosphere. Rhizosphere oxygenation promotes aerobic metabolisms increasing CO2 emissions, yet the effect on CH4 can be variable: it may enhance soil organic matter breakdown into small molecules such as acetate - potentially fueling CH₄ production - or suppressing methanogenesis. Currently, it is uncertain whether the combination of rhizosphere oxygenation and organic exudation in anoxic soils contributes to more production of climate-relevant GHGs or whether it has a suppressing effect.
To tease apart the individual and combined effects of rhizosphere oxygenation and organic exudation on thawed permafrost soil biogeochemistry and GHG fluxes, we incubated soil obtained from a fully thawed site in Stordalen mire, Sweden, under anoxic conditions. The soil was subjected to one of four treatments via an artificial root: a non-spiked control; organic exudate-mix alone (added three times a week); continuous ambient air addition; and a combination of both organic exudate mix and air. Concentrations were chosen to mimic plant release amounts under field conditions. Porewater geochemistry analysis is combined with extractions of organic carbon and iron precipitated on the artificial root and discussed along headspace GHG data and microbial functional gene profiling.
Organic exudate-mix alone strongly increased both CO₂ and CH₄ emissions, accompanied by substantial mobilization of iron and organic carbon. In contrast, the addition of air - either alone or combined with organic exudation - decreased CH₄ and CO₂ emissions. Decreased CH4 may potentially be caused by thermodynamic suppression of methanogenesis by less reducing soil conditions as indicated by less mobilized and more oxidized iron. Based on the used amounts of organic carbon and air inputs and the chosen lab incubation parameters, the combination of organic exudation and oxygenation could lead to less stimulation of GHG production as anticipated from classic priming studies.
How to cite: Mollenkopf, M., Haas, L., Kappler, A., and Muehe, E. M.: Rhizosphere oxygenation decreases greenhouse gas emissions from thawed permafrost soil, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12854, https://doi.org/10.5194/egusphere-egu25-12854, 2025.
Climate warming and associated permafrost thaw can have multi-faceted impacts on carbon fluxes from inorganic and organic sources. Permafrost thaw unlocks large stores of organic carbon that can be mineralized and emitted as carbon dioxide (CO2) from rivers to the atmosphere, or transported downstream. Concurrently, permafrost thaw exposes minerals to weathering reactions that can both sequester or emit carbon. Finally, climate warming can affect reaction kinetics and the cycling of reactive fluids through the subsurface. To date, the tradeoff between these competing effects and their net effect on landscape-scale carbon fluxes remain unclear.
Here, we present fluxes of dissolved solutes, riverine CO2 emissions, and carbon-isotope data from rivers that drain over 700,000 km2 of the Qinghai-Tibet Plateau, and that span a gradient in permafrost cover and temperature. Our data provide evidence for an interplay of organic-carbon degradation and inorganic chemical weathering that appear to modulate the balance of carbon sinks and sources. We find that net CO2 drawdown-fluxes from rock-weathering across the region account for ~35% of river CO2 emissions. Importantly, chemical weathering and organic carbon fluxes vary across the sampled permafrost gradient. In catchments underlain by continuous permafrost, CO2 drawdown from chemical weathering accounts for only ~25% of riverine CO2 outgassing. Conversely, carbon drawdown from weathering substantially outpaces riverine emissions in catchments with discontinuous or isolated permafrost.
Based on these results, carbon fluxes from chemical weathering may become increasingly important with ongoing permafrost thaw, potentially even outpacing riverine CO2 emissions. In landscapes where carbonate and silicate weathering dominate – such as over a large part of the QTP – a substantial portion of additional CO2 production from permafrost thaw could, therefore, be buffered by weathering on human timescales.
How to cite: Bufe, A., Zhang, L., Dean, J. F., Rocher-Ros, G., Stanley, E. H., Sponseller, R. A., Butman, D. E., Karlsson, J., Liu, R., and Battin, T. I.: Impacts of warming and permafrost thaw on chemical weathering and riverine carbon fluxes on the Qinghai-Tibet Plateau, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5063, https://doi.org/10.5194/egusphere-egu25-5063, 2025.
Permafrost affected soils and especially Yedoma deposits contain a huge amount of carbon and nitrogen, which can be released and become available after thawing. Coastal and thermal erosion, e.g. in drain lake basins, are important processes for the release and transport of reactive nitrogen and carbon from soils to the aquatic environment and consequently to the coastal waters and the Ocean. The faster warming of the Arctic in relation to the rest of the world will amplify the rate of release of nitrogen and carbon.
To understand the hydrological conditions and release pathways of the thawing nitrogen and carbon, we investigated a drained lake basin (Schaeffers Lake) and a Yedoma Cliff (Cape Blossom) at the Baldwin Peninsula, Alaska. Samples from rain, snow, ice wedges, outflow water, basin water, pore water and soil were taken. By measuring biogeochemical properties (dissolved inorganic (DIN)and organic nitrogen (DON) plus 15N stable isotopes, DI13C/TA, 18OH2O, dissolved gases (CO2, methane and N2O) et al.), we want to unravel the path of the water and how carbon and nitrogen are enriched and transported.
First results show that the out-flowing water contained a considerable amount of DIN and DON, the 15N stable isotopes of nitrate were significantly enriched and the water was oversaturated with methane and N2O. This indicates that not only reactive nitrogen is released by the thawing and erosion, but also quickly processed by microbial activity that is stimulated by the nutrient input.
How to cite: Sanders, T., Meyer, H., van Dam, B., Marushchak, M., Hashmi, W., and Treat, C.: Following the water.: The thawing and erosion of permafrost increase input of reactive nitrogen and carbon to the coastal water at the Baldwin Peninsula, Alaska, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15836, https://doi.org/10.5194/egusphere-egu25-15836, 2025.
Nitrous oxide (N₂O) is one of the most important greenhouse gases (GHG) with a global warming potential about 298 times stronger than carbon dioxide (CO₂) over a period of 100 years. While most N₂O emissions are released from natural ecosystems (60%), research has focussed largely on nutrient-rich agricultural soils, leading to a lack of understanding of nutrient-poor (sub-) Arctic ecosystems. Recent findings indicated significant N₂O emissions from organic-rich Arctic soils, resulting in a bias towards high emitting sites and particularly poor knowledge on N₂O consumption. As a result, the contribution of N₂O fluxes from the (sub-) Arctic regions to the global budget remains highly uncertain. Recent advances in portable gas analysers have improved our ability to measure low in-situ N₂O fluxes. To study the impact of environmental drivers (e.g. soil moisture, temperature, and photosynthetically active radiation) on N₂O fluxes using a portable N₂O analyser, we conducted chamber-based field measurements across a thaw gradient (palsa to bog to fen) in a sub-Arctic permafrost peatland in northern Sweden (Stordalen mire, Abisko), covering May to September. Conducting light (transparent) and dark (opaque) measurements, we found that soils in the Stordalen mire show a light-dependency, emitting N₂O in light conditions with a median of 0.56 µg m-2 h-1 (n = 480), and consuming N₂O in dark conditions with a median of -1.36 µg m-2 h-1 (n = 478). Since these changes can happen very rapidly, potential drivers of this dependency could be different active microbial communities, or vegetation impacts through photosynthesis. These results suggest that measurements with both transparent and opaque chambers are crucial for future N₂O flux studies to accurately estimate the N₂O budget. Generally, we measured low N₂O fluxes with a median flux of 0.02 µg m-2 h-1, of which all flux rates were above the minimal detectable flux. However, we also found one hot spot which continuously emitted high N₂O fluxes, with a maximum of 159.43 µg m-2 h-1 compared to 4.38 µg m-2 h-1 for all other plots. These are novel findings, suggesting that complex N₂O dynamics occur in nutrient-poor sites and further investigations are needed to understand the processes underlying the N₂O fluxes.
How to cite: Triches, N. Y., Marushchak, M. E., Engel, J., Virkkala, A.-M., Hashmi, W., Rovamo, M., Vesala, T., Lamprecht, R., Heimann, M., and Göckede, M.: First extensive manual N₂O flux measurements reveal a light-dependent N₂O sink in a thawing permafrost peatland, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8907, https://doi.org/10.5194/egusphere-egu25-8907, 2025.
Nitrous oxide (N₂O) is a critical greenhouse gas, ranking third in prevalence and serving as the leading contributor to ozone depletion in the twenty-first century. Its global warming potential is 298 times higher than that of carbon dioxide (CO₂) over a 100-year timeframe. Current estimates suggest that global N₂O emissions range from 8.1 to 30.7 teragrams (Tg) per year. Alarmingly, about two-thirds of these emissions stem from natural terrestrial sources, mainly related to microbial processes in soils. While significant research has focused on microbial mechanisms driving N₂O emissions in nutrient-rich ecosystems, there is an urgent need to address the limited knowladge on N₂O fluxes and underlying microbial mechanism in low-nutrient regions, such as Arctic ecosystems.
Many Arctic soils hold very low amounts of available nitrogen, leading to the assumption that they do not produce N2O in measurable quantities. However, recent advances with portable gas analyzers have made it possible to successfully capture low fluxes, which are important for the nitrous oxide budget of areas covering vast tundra landscapes, challenging this perception. Additionally, diurnal variations of nitrous oxide fluxes are rarely taken into account. In our study site, the Stordalen palsa mire (Abisko, Sweden), a diurnal variation in N2O emissions has been observed with chamber methods, with notably higher net emissions during the daytime and atmospheric N2O consumption in the night. This study aims to delve deeper into the geochemical and microbial mechanisms behind this intriguing phenomenon.
We conducted round-the-clock microbiological and geochemical sampling, along with N2O flux measurements, in the Stordalen Mire, Abisko, Sweden. Our research reveals significant insights into the availability of soluble nutrients, which were markedly higher during the daytime than at night. In our exploration of N2O consumption and production, we meticulously quantified the activity of N2O exchange-related genes responsible for N2O flux at the transcript level—specifically the denitrification genes (nirK and nirS) and N2O consumption genes (nosZ)—and analyzed their association with the day-night N2O flux phenomenon, followed by RNA sequencing. Remarkably, we found that microbial gene expression patterns closely correlate with the flux data and geochemical trends. Consequently, our day-night flux measurements, paired with thorough geochemical and microbiological analyses, provide critical undestanding into the diurnal variations in N2O fluxes within Arctic ecosystems. Our findings provide new insights into how microbes mediate complex N2O flux dynamics in nutrient-poor Arctic ecosystems during day and night, underscoring their significance in the global nitrogen cycle.
How to cite: Paul, D., Hashmi, W., Triches, N. Y., Znaminko, M., Siljanen, H. M. P., Biasi, C., Göckede, M., Mammarella, I., and Marushchak, M. E.: Unraveling the microbial mechanism responsible for diurnal patterns in N2O fluxes in a subarctic permafrost peatland, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12246, https://doi.org/10.5194/egusphere-egu25-12246, 2025.
Permafrost thaw, wildfires, and increased amplitude of floods and droughts are all aspects of climate change that risk affecting the downstream mobilization of dissolved organic carbon (DOC), the neurotoxin methylmercury (MeHg), and various nutrients from boreal peatlands. In this study, we monitored water chemistry at the outflow of eighteen peatland-rich catchments (125 – 1700 km2) across a climate gradient in boreal western Canada. Our study included a wetter year (2022) and two extreme drought years (2023 and 2024) which also resulted in extensive fires that affected nine of the watersheds in 2023. Flood conditions in 2022 resulted in high hydrological connectivity, particularly in comparison to 2023 and 2024, where drought conditions coupled with extensive wildfires limited connectivity and combusted existing carbon stores. This reduced the mobilization of the co-transported MeHg in streams during the drought years, as well as resulting in no observable effects of the wildfires overall on water chemistry due to this limited connectivity within the peatlands.
Peatlands, covering over 30% of the Dehcho Region and Hay River watershed, are likely the primary source of these deleterious solutes due to the biogeochemistry of anoxic waterlogged soils. The goals of this monitoring program were developed collaboratively with the Dene Tha’, K'atl'odeeche, and Dehcho First Nations; their perspectives have been critical for this project. Community members expressed concerns about declining water quality potentially related to climate change, and the associated impacts on ecosystem health and fish resources. To assess the temporal variability of water quality, we studied four creeks with similar catchment sizes and peatland extent along a permafrost gradient using in-situ field sensors and grab samples. Additionally, a Before-After-Control-Impact methodology was used to evaluate the impacts of wildfires on water quality in eighteen streams along a permafrost gradient to assess northern vulnerability. Previous research has observed that peatlands in the discontinuous permafrost zone have poorer hydrological connection to the stream network compared to peatlands south of the permafrost boundary, resulting in higher solute concentrations in the southern region extent. Higher flow conditions during the spring resulted in minor peaks in MeHg and DOC concentrations, with decreasing concentrations as freshet ended. However, warmer temperatures that accelerate microbially associated DOC and MeHg generation resulted in the highest annual concentrations, despite extreme drought conditions that should’ve limited surface water sourcing.
Understanding the interactive impacts of permafrost conditions, wildfire and inter-annual climate variability on water quality is essential for managing and protecting the health of northern communities, ecosystems, and food webs. This research provides vital data to inform decision-making, support the resilience of local First Nations, and guide effective environmental stewardship in the face of ongoing climate change. We believe our findings are likely representative of northern peatland-rich regions broadly and will thus be of great interest to understand the global impacts of permafrost thaw and wildfire on carbon and mercury cycling.
How to cite: Mandour, F., Greyeyes-Howell, J., Shewan, R., Thompson, L., Graham, I., Low, M., Munson, M., Connon, R., and Olefeldt, D.: Fire, drought and permafrost thaw: interactive effects on dissolved organic carbon, mercury, and nutrients in peatland-rich watersheds of boreal western Canada. , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7822, https://doi.org/10.5194/egusphere-egu25-7822, 2025.
Permafrost is changing rapidly as it continues to thaw, releasing mercury (Hg) and potentially creating hotspots for Hg methylation as organic matter decomposes. If Hg is remobilszed and bioaccumulates as methylmercury (MeHg) in food webs, it could pose a serious health risk to northern communities and wildlife. Here, we have investigated cycling of Hg in five peatlands of northern Scandinavia, that are underlain by sporadic permafrost. To investigate natural thaw gradients, we sampled a total of 47 peat plateau cores that are representing intact permafrost conditions, and 47 fens soil cores, representing thawed permafrost conditions and characterized them based on their distribution of total Hg, MeHg and organic matter. Where permafrost peat had degraded into wet fens, we found that total Hg levels were lower compared to the dry peat plateaus, while MeHg were higher upon thaw. Our results suggest a significant Hg loss and potentially increased methylation due to thermokarst in permafrost-affected peatland ecosystems. A large spatial coverage of sampling locations allows us to investigate the distribution, the variability and transformation of Hg on a regional scale, thereby improving our understanding of Hg mobility from thawing permafrost in northern Scandinavia.
How to cite: Haugk, C., Jonsson, S., and Azaroff, A.: Mercury mapping in northern Scandinavian permafrost peatlands , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-989, https://doi.org/10.5194/egusphere-egu25-989, 2025.
The greenhouse gas (GHG) balance of northern peatlands is being influenced by the combined effects of rapid permafrost thaw and increasing frequency and severity of droughts. Our soil chamber flux measurements revealed that thermokarst fens in the discontinuous permafrost zone of boreal western Canada (Lutose, Alberta) acted as stronger net sources of carbon dioxide (CO2) and consistently emitted more methane (CH4) than thermokarst bogs during two extreme-drought years. Peatlands in the discontinuous permafrost zone store large amounts of soil carbon, but thawing permafrost results in changes to hydrology and vegetation, which have the potential to substantially impact their greenhouse gas balance. As permafrost thaws, thermokarst bogs and fens develop and expand, further modifying GHG dynamics. Although thermokarst fens account for approximately 30% of peatlands in the discontinuous zone, they have received little attention, and there is limited understanding of how the GHG balance varies along the trophic gradient from poor fens to extreme-rich fens.
This study explored the spatial and temporal variability of greenhouse gas fluxes across four sites, including a thermokarst bog, poor fen, rich fen, and an extreme-rich fen. Trophic status of each site was classified based on pH, electrical conductivity (EC), vegetation, and concentrations of magnesium (Mg) and calcium (Ca). Fluxes were measured over two growing seasons and one winter (June 2023 to October 2024). Controls on greenhouse gas fluxes were explored using data on vegetation composition, water chemistry, hydrology, and climatic conditions. Our analysis showed that CH4 emissions generally increased along the trophic gradient, with the exception of the extreme-rich fen, where high sulfate concentrations suppressed emissions. Non-growing season CH4 emissions were also a significant contributor to annual emissions across all sites.
Overall, our findings indicate that trophic status plays an important role in determining the greenhouse gas balance of thermokarst bogs and fens following permafrost thaw. Understanding the drivers of the carbon dioxide balance and methane emissions in these ecosystems during extreme drought years is essential for refining models of peatland carbon dynamics and predicting their future role in the global carbon cycle as climate change continues.
How to cite: Kempton, K. and Olefeldt, D.: Greenhouse gas balance of thermokarst fens and bogs in the discontinuous permafrost zone during extreme drought years, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4987, https://doi.org/10.5194/egusphere-egu25-4987, 2025.
With climate change, discontinuous permafrost is thawing rapidly and part of Permafrost-affected peatlands are at risk of disappearing within decades. Thawing in permafrost-affected peatlands can occur gradually (decades to centuries) or abruptly (weeks to years). While abrupt degradation is less frequent, it may contribute to higher carbon (C) loss. However, predicting C loss with permafrost thaw from organic-rich soils, such as in Palsas, remains challenging. This highlights the need for laboratory studies focused on biogeochemical and hydrological changes, as well as C emissions during permafrost thaw. In this study, we simulated a gradual and an abrupt Palsa degradation under varying hydrological conditions to observe the impact of these different scenarios on the degradation rate of organic matter (OM). We used a meso-scale incubation setup to continuously measure CO2 and CH4 emissions, while deepening the permafrost table with three thaw stages over the 90 days duration of the incubation. This approach enabled the quantification of C contribution from deeper layers. Additionally, we assessed the OM degradation stage by using a FTIR approach. Our results showed a net CH4 uptake for all the Palsa cores and a twofold increase in CO2 emission rates following the thawing events for all the treatments simulating abrupt thaw (flooded conditions). We found that the physical disruptions of macro-agglomerates and redox changes due to the flooding enhanced OM lability in the active layer. In contrast, deepening the permafrost table increased emissions from Palsa cores under gradual thaw by a factor of two (dry conditions), while CO2 emissions remained constant under the abrupt thaw simulation. This outcome supports higher C contribution from permafrost layers under dry conditions. Finally, the increase in CO2 emissions with thaw from the saturated peatland highlight the potential role of deep-rooted vegetation as a transport pathway for CO2 in water-saturated soils outside the growing season.
How to cite: Laurent, M., Schaller, J., Baysinger, M. R., Lück, M., Hoffmann, M., Windirsch, T., Ellenbrock, R. H., Strauss, J., and Treat, C. C.: Enhanced CO2 Emissions Driven by Flooding in a simulation of Palsa Degradation, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8852, https://doi.org/10.5194/egusphere-egu25-8852, 2025.
Palsa mires are located at the southern border of the permafrost zone making them highly sensitive to climate warming. When annual temperature and precipitation conditions are optimal, palsas form and collapse in a natural cycle. However, due to current climate warming, permafrost is widely thawing and palsas are degrading rapidly. In addition to being unique and valuable habitats for many species, palsas store significant amount of ancient carbon (C), which is released by reactivated decomposition processes when permafrost thaws, potentially changing the peatlands temporarily from C sinks to C sources. However, the age and extent of the C released remain uncertain.
To predict how palsas will respond to ongoing climate change, understanding of the past dynamics is vital. In this study, we determined the permafrost aggradation date and reconstructed the past dynamics of a palsa in Karlebotn, northern Norway. A peat profile was radiocarbon (14C) dated, and oribatid mite analysis together with a peat type analysis and peat properties (C, nitrogen and bulk density) were performed. Oribatid mites are a diverse group of soil-living arthropods that have shown potential as environmental indicators. Recent findings suggest they can indicate the past initiation of permafrost.
Our results suggest that gradual permafrost aggradation at the Karlebotn palsa began after 1500 calibrated years Before Present (cal yr BP; present = 1950 AD) and that at 700 cal yr BP the permafrost conditions had stabilized. Using multiproxy analysis, we identified three phases in the palsa history. The first phase was characterized by moist fen conditions, the second phase was a transition phase with wet and dry condition species occurring together and the last phase was dominated by species adapted to dry conditions, and which are typical in permafrost environments. Our data also indicate that during permafrost conditions, the C accumulation rate was lower than in the early non-permafrost fen stage. While permafrost thaw will temporarily increase C emissions, the C sink capacity may ultimately increase again as the peatland shifts back to a fen stage following ground subsidence.
Only few palaeoecological studies exist from Fennoscandia where age of permafrost formation is determined. Most studies have used vegetation succession and peat properties to infer past permafrost presence, however, these methods are associated with uncertainties such as the absence of permafrost indicator plant species. This study provides additional data on historical palsa dynamics with a relatively robust chronology, based on multiple proxies, including oribatid mite community analysis. These findings contribute to our understanding of how palsas are responding to the ongoing and future climate change.
How to cite: Kiss, E., Kuosmanen, N., Sannel, A. B. K., and Väliranta, M.: Multiproxy analysis of peatland permafrost initiation in northern Norway, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6261, https://doi.org/10.5194/egusphere-egu25-6261, 2025.
Soil moisture is one of the key variables controlling the exchanges of water and energy at the land surface. One particularly interesting climate zone is the Eastern Tibetean Plateau with its dry cold winters and wet monsoon summers at high altitudes. To better understand hydrological processes and the response of the hydrological cycle to climate change the novel method of Cosmic-Ray Neutron sensing had been tested in the northeast of the Qinghai-Tibet Plateau with a highly hetereogeneous organic soil profile. Using this technique one can relate the flux density of albedo neutrons generated in cosmic-ray induced air showers to the amount of water in the environment on the scale of several hectares. Instrumented with in-situ sensors and cosmic ray probes we discuss the effective measurement depth of CRNS retrieval and vertical weights of different layers up to 50 cm depth in this semi-humid alpine meadow. During the non-frozen period we analyzed and validated the representativeness of CRNS in an extensive comparison of in-situ data, two soil moisture retrieval algorithms and full-scale neutron Monte Carlo simulations using the transport model URANOS. As the CRNS method gains traction and evolves towards large-scale applications, the findings from this study are pivotal for the understanding of the technology and its limitations.
How to cite: Köhli, M., Marach, J., Liu, R., Wang, X., and Wang, Z.: Peatland hydrology: From tropical to subarctic latitudes, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19897, https://doi.org/10.5194/egusphere-egu25-19897, 2025.
Palsas are a permafrost landform found in northern peatlands, characterized by peat mounds with a frozen core. Climatic changes cause widespread degradation of palsas, affecting biodiversity, hydrology, carbon fluxes, and local infrastructure. Therefore, palsa mires are considered a priority habitat under the EU Species and Habitat Directive and are integrated into Sweden’s environmental goals, such as maintaining Thriving Wetlands. Despite their threatened status, the largest coherent palsa mire in Sweden, Vissatvuopmi (N68°47’, E21°11′), has no protective status. At this site, we monitor several palsas and peat plateaus, using a wide range of methods to understand both exterior and interior dynamics. We use a UAV with a LiDAR scanner to obtain high-resolution terrain models and track topographical changes. Between September 2022 and September 2024, we observed several “degradation hotspots” that undergo rapid collapse. Annual LiDAR data are supported by UAV orthophotos and the monitoring of active layer thickness, ground temperatures in six boreholes (2–6 m deep), and the local climate. Regarding the palsas’ interior, we present a comprehensive pseudo-3D survey of Electrical Resistivity Tomography (ERT). The results indicate that the shape of the frozen core on a palsa is highly heterogeneous, with a maximum depth roughly three times the height of the palsa. Finally, cores down to 5 m reveal a thick (up to 2 m) peat layer and thick ice lenses at depth. This multi-method approach provides a comprehensive view of palsas’ structure and will help advance our understanding of how peatland permafrost responds to a rapidly changing climate.
How to cite: Renette, C., Fuentes, M., Liljebladh, B., Pavoni, M., Peternell, M., Stridbeck, P., Thorsson, S., and Reese, H.: Mapping and Monitoring of Sweden’s largest coherent palsa mire, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6749, https://doi.org/10.5194/egusphere-egu25-6749, 2025.
Permafrost stores large amounts of organic matter. As warming-induced thawing, this organic matter becomes accessible for microbial decomposition, potentially leading to substantial nitrous oxide (N₂O) emissions. However, previous studies have primarily focused on rapid permafrost collapse and its effects on N₂O fluxes, the impact of gradual thawing of active layer remains unclear. Here, we conducted a whole-ecosystem warming experiment on the Tibetan permafrost region to simulate a 2°C increase in ecosystem temperature accompanied by increasing active layer. In-situ monitoring of N₂O fluxes was combined with 15N site preference (SP) and δ18O isotopomers of N2O, microbial high-throughput sequencing, and meta transcriptomics to elucidate the change in N₂O emissions upon the increasing thawing of active layer and its underlying mechanisms. Our results reveal an asymmetric response of N₂O fluxes to thawing of active layer throughout the growing season. In the early growing season, thawing increased N₂O fluxes by 261 %, with significant changes in δ18O and SP, as well as change the soil organic matter, microbial diversity, and activity. In contrast, no significant effects were observed in the later season. These findings suggest that, during early-season, thawing accelerates nutrient release, alleviating nitrogen competition and promoting microbial growth, which enhances nitrification-driven N₂O emissions. During later-season, plant nutrient depletion intensifies competition, suppressing microbial activity and N₂O fluxes. This study is the first in-situ to report N₂O emissions in response to gradual active layer thawing, providing important evidence for understanding ecosystem responses to climate change.
How to cite: Zhou, W., Yang, G., and Yang, Y.: Asymmetric response of nitrous oxide emissions to active layer thawing in permafrost, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5761, https://doi.org/10.5194/egusphere-egu25-5761, 2025.
Northern peatlands store large amounts of carbon (C) as well as nitrogen (N) which amounts to ∼80 % of global C and N peatland stocks, making them important C and N reservoirs. With Arctic amplification warming the Arctic nearly four times faster than the global average, an increased permafrost thaw was observed even in very cold polar regions such as the Canadian High Arctic, where thaw depths already exceeded scenarios projected to occur by 2090, altering hydrology, geomorphology as well as nutrient cycling in the landscape, caused by but not limited to increased thermokarst formation. Thermokarst describes a landscape occurring when ice-rich permafrost, which is highly vulnerable to climate change due to lack of sufficient thermal buffering, thaws altering microbial decomposition of soil organic matter (SOM), including N pathways. Considering the effects of global warming on permafrost-affected peatlands in the Arctic, it is likely that the active layer will continue to deepen and thaw more and more permafrost and therefore, expose more formally frozen SOM to microbial decomposition, priming the N-cycling and increasing the N availability.
Our work explores the changes in N-cycling in thermokarst landscapes, by incubation of soils with 15N stable isotope tracing to assess organic N depolymerization, N-mineralization and nitrification rates over time. Permafrost soils from the continuous permafrost zone on the uplands east of the Mackenzie Delta (Northwest Territories, Canada) from 3 different depths in the active layer and the upper permafrost, in two phases of thermokarst development were investigated. We performed a 15N tracing experiment, by incubating soils with a 15N-protein for 9 days and estimated 15N in dissolved organic N, microbial N and nitrate as well as ammonium.
Our results show changing N-cycle processes with depth, as well as with progress of thermokarst stages. Generally microbial N uptake in active layers was favoured over N mineralization, while the contrary was the case in permafrost layers. This pattern might be connected to a microbial N-limitation in the upper soil layers leading to increased microbial N demand. In permafrost layers microbes show higher rates of N mineralization (ammonification), i.e., they excrete inorganic N, most likely because of a carbon limitation. With progressing thermokarst development a shift form microbial uptake focused processes to mineralization pathways was observed in the active layer. This trend might be due to increased N availability as ground collapses as a result of thawing and mixes the soil layers, leading to decomposition of previously frozen SOM. Permafrost layers favoured ammonification, however, samples from secondary thermokarst sites showed signs of N limitation at the end of incubation, most likely because of the long-term exposure of microbes to available SOM leading to depletion of the N stocks.
With this work we contribute to unravelling the changes in N-cycle pathways in the thawing Arctic, shining a light on the consequences of climate change on these remote ecosystems.
This study was funded by the Marie Skłodowska-Curie Actions H2020-MSCA-IF-2020 within “NITROKARST” project (Grant agreement 101024321)
How to cite: Mayer, M., Martin, V., Fuchslueger, L., Richter, A., and Valiente, N.: Effects of permafrost thaw on N-cycle processes in a thermokarst system, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18338, https://doi.org/10.5194/egusphere-egu25-18338, 2025.
Permafrost soils in the Arctic region contain vast amounts of frozen dead biomass, composed of twice the amount of carbon (C) as in the atmosphere and a great quantity of nutrients. Due to climate change, these soils are thawing at greater depths each summer and will continue to do so in the future, rendering this frozen organic material accessible to decomposition. Most research thus far has focused on the amount of C that could potentially be released as CO2 and CH4 gases through the decomposition. However, the release of nitrogen (N) is estimated to have a significant impact on the region's ecosystems and global greenhouse gas budgets, as this excess N may boost vegetation growth, potentially enhancing its CO2 uptake. However, it could also lead to increased N losses in the form of N2O emissions and lateral export to water bodies. This research aims at synthesizing the historical and future changes of the terrestrial N budget in the Arctic following permafrost thaw.
Here, we provide estimates of past and future changes to the pan-Arctic N budget and how it is affected by permafrost thaw. We combine soil nitrogen data from Palmtag et al (2022) and CMIP6 model projections of active layer depth. The amount of N released through permafrost thaw is compared to estimates of changes in N deposition and biological fixation. Furthermore, we quantify the biologically available fraction of the N released from the permafrost and provide a first-order estimate on the consequences of this altered N cycling for Arctic vegetation biomass growth and CO2 uptake based on published results from N fertilization field experiments.
Based on CMIP6 model output, we estimate that the mean active layer depth over the whole Arctic permafrost region will increase from an averaged depth of 1.3 m for the present day to 2.3 m depth following SSP 126, to 3.6 m depth following SSP 370, and to 3.9 m depth following SSP 585 scenarios for the time period 2080 - 2100. The additional N mobilized through this permafrost thawing translates to increases of 95 %, 167 % and 186 % of nitrogen in the active layer compared to present day. By 2100, with N inputs from permafrost thaw and assuming that 5 - 15 % of this becomes available as plant nutrition, vegetation biomass could increase by 16 – 50 g C m-2 yr-1, 31 – 96 g C m-2 yr-1, or a 35 – 106 g C m-2 yr-1 for the SSPs 126, 370 and 585, respectively, assuming a linear increase in vegetation biomass growth until 2100. These numbers would reflect a significant additional drawdown of CO2 by the pan-Arctic vegetation, with relevance for global assessments.
Figure 1: Timeseries showing the amount of additional N in kg N / m2 in the active layer, anomaly to 1880-1900. The dotted line indicates the change from observation-based models to future projection based on the SSP scenarios.
How to cite: Oxley, L., Lacroix, F., Stocker, B., and Zaehle, S.: Quantifying Changes to the Arctic N Budget following Permafrost Thaw, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18446, https://doi.org/10.5194/egusphere-egu25-18446, 2025.
About 15 % of the northern hemisphere is covered by permafrost, which is subjected to climate change and therefore drastically changing conditions for soil microorganisms. Progressing permafrost thaw could enable formerly inactive microorganisms to (re)gain activity and metabolize carbon. Methane (CH4) is a biogenic greenhouse gas (GHG) that is approximately 28 times more potent than carbon dioxide (CO2) on a 100-year time horizon. It is currently not well understood how the emissions of this potent GHG from permafrost-affected soils will be changing under the effects of climate change.
It was suggested that during freeze-thaw-cycles and even during winter, Arctic tundra soils emit substantial amounts of methane but since sampling in permafrost regions is logistically intricate, there is a low study coverage. Here, we present molecular data of four distinct field campaigns on Disko Island, West Greenland. The studies encompass three years (2022 to 2024) and three different seasons: September – time of maximum active layer depth, July – initial annual thawing period, and April – completely frozen soil with snow cover. We sampled two moisture transects in permafrost-affected soils, each from higher elevation with dry soil towards lower elevation, with soil almost completely water saturated. The soil moisture gradients were chosen, because they are potentially important drivers of the ratio between CH4 oxidation vs. production throughout the seasons. Each plot was sampled in triplicates to varying depths of 10 cm to up to 90 cm. The samples were taken from identified soil horizons and DNA for metagenome analysis was extracted. The resulting total of 235 samples over all four sampling seasons were used for 16S rRNA gene metabarcoding (Illumina) to investigate the microbial community diversity over the different sampling seasons.
Methane oxidizers (methanotrophs) were constantly abundant but accounted for less than 1 % of the relative abundance across the samples. The abundance of methane producers (methanogens), mostly Methanobacterium spp., substantially changed throughout the different time points, locations and depths, and accounted at times for over 20 % of relative abundance of all prokaryotes while being completely absent in other samples.
Additional quantitative PCR (qPCR) analyses have revealed distinct distributions of both pmoA (gene for a membrane-bound enzyme for oxidizing methane) and mcrA (gene for the final step of biological methane production) for September 2022, with a higher methanogenic gene abundance in deep and wet samples. This was confirmed through incubation experiments and subsequent gas analyses in the laboratory. Further qPCR will reveal the CH4-oxidation and -production potential for the other time points. Accompanying to this, other environmental parameters (H2O content, season, pH) will allow to assess potential key factors for methanogenesis vs. methanotrophy in a final correlation approach.
Our results show that permafrost-affected soils harbor a surprisingly large spatiotemporal variability in community composition and abundance of methanogens while the methanotroph community seems to be comparably stable. These findings have implications for future GHG budget calculations of the Earth, as this suggests that methanotrophs and methanogens would react very differently to Earth’s changing climate and resulting environmental changes, such as water saturation of soils.
How to cite: Bruhn, C., Gasimova, P., Voigt, C., Knoblauch, C., Peplau, T., Liebmann, P., Guggenberger, G., Melchert, J. O., and Liebner, S.: Dynamic Methanogens – Persistent Methanotrophs: Shedding Light on Microbial Communities of the Methane Cycle Across Seasons in Permafrost-Affected Soils in West Greenland, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-21721, https://doi.org/10.5194/egusphere-egu25-21721, 2025.
Thermokarst lakes have been widely observed to function as strong atmospheric methane (CH4) sources. The warming-induced development of thermokarst lakes is simultaneously accompanied by a considerable release of nutrients, which may in turn exhibit reverberation on CH4 emissions. However, the effect of a coupled carbon and nutrient cycle on CH4 emissions has yet been explored in any experimental studies. Here, by conducting in-situ nutrient addition experiments at two representative sites, coupled with incubating sediments from thermokarst lakes at 30 sites across a 1,100-km permafrost transect on the Tibetan Plateau, we explore the response of CH4 emissions to nutrient input across thermokarst lakes. We find that nitrogen input accelerates CH4 emissions by 38.6-54.4%, while phosphorus input doesn’t generate additional effects. Random forest model analysis reveals that methanogen is the dominant driver for the intensity of positive nitrogen effect, which is confirmed by the increased RNA-methanogenic abundance after nitrogen input. These results demonstrate that nutrient release upon permafrost thaw will enhance CH4 emissions from thermokarst lakes, highlighting that their enhancements should be considered by land surface models when projecting CH4 fluxes in permafrost regions under warming climate.
How to cite: Zheng, Z., Yang, G., and Yang, Y.: Methane emissions from thermokarst lakes amplified by nutrient release upon permafrost thaw, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5785, https://doi.org/10.5194/egusphere-egu25-5785, 2025.
Arctic warming is facilitating the encroachment of trees into tundra landscapes. Trees at the forest-tundra ecotone are typically small, slow-growing and show high mortality rates. Tree necromass enters the soil as root, leaf and stem litter. This material can be decomposed or contribute to long-term soil organic matter stocks, as well as change decomposition of native soil organic matter (priming). We here tested whether decomposition processes change under dying spruce trees in tundra soils in a controlled laboratory experiment. The opportunity for addressing this question came up within a laboratory macrocosm experiment on the effect of various living tundra plants on carbon and nitrogen cycling in a tundra soil. For this experiment, root-picked soil was homogenized and filled into macrocosms, reconstructing the original horizon sequence. Plants with washed roots were placed in the soil and macrocosms watered regularly from the top. The small (ca. 50 cm) spruce trees died early in the experiment, and we kept the experiment running to assess changes in carbon and nutrient cycling resulting from the decomposition of spruce necromass compared to the plant-free control soil. Pore gas CO2 concentrations at 7 cm depth were significantly higher in spruce than in the control soils. We further observed significantly lower pH values, as well as significantly, ca. 25% lower potential activities of hydrolytic (leucine-aminopeptidase, cellobiohydrolase, N-acetyl-beta-D-glucosaminidase), but not oxidative extracellular enzymes. These findings suggest that the input of root and needle-leaf litter altered the functioning of the soil decomposer community. These differences extended into the deeper soil below the rooting zone of spruce plants, pointing at an important role of leaching. These first observations will be compared with surface CO2 fluxes, dissolved organic and microbial carbon concentrations to dissect the decomposition dynamics of spruce necromass at the forest-tundra ecotone.
How to cite: Wild, B., Rijkers, R., Sauerland, L., Wegner, R., Carter, A., and Frey, L.: Death of a spruce: Soil decomposition processes under dying spruce trees at the forest-tundra ecotone, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8271, https://doi.org/10.5194/egusphere-egu25-8271, 2025.
The Arctic is warming rapidly, causing permafrost thaw and vegetation shifts. As a result, shrubs and trees from lower latitudes are encroaching into the tundra, altering biomass distribution above and below ground. These changes impact greenhouse gas (GHG) emissions by influencing litter input, root distribution, and microbial activity. A key mechanism in GHG production in soils is the rhizosphere priming effect, where labile carbon inputs from plants into the soil stimulate microorganisms to produce enzymes that decompose both labile and recalcitrant soil organic matter (SOM). However, the effects of rhizosphere priming on SOM decomposition and its influence on greenhouse gas emissions under natural conditions remain poorly understood. To address this, we simulated sub-Arctic vegetation changes in a controlled environment using tundra soil and plants sampled from the Northwest Territories, Canada. The soil was processed, homogenized, and placed into macrocosm chambers while preserving the original horizon sequence. The experiment included four vegetation types and one control, with plant species that are characteristic for the transition from sub-Arctic to lower Arctic bioclimate zones and included a small tree (Picea mariana), deciduous shrubs (Betula glandulosa, Alnus viridis) and graminoids (Eriophorum vaginatum, Carex sp.). Over three months, representing one growing season, weekly soil pore gas samples were taken at different depths, and surface efflux was measured additionally every three weeks. Preliminary results indicate that soil pore gas concentrations of CO2 increased with depth and over the experiment's duration across all vegetation groups and the control, and showed variability among vegetation types. Soil pore gas concentrations will be compared with soil efflux, dissolved organic carbon, microbial carbon contents, extracellular enzyme activity, and other parameters currently under evaluation. These data will help us to elucidate the role of woody plant species for permafrost soil processes and their contribution to GHG production in Arctic tundra ecosystems.
How to cite: Frey, L., Carter, A., Rijkers, R., Sauerland, L., Wegner, R., and Wild, B.: Effect of changing tundra vegetation on greenhouse gas emissions from Arctic permafrost soil, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8342, https://doi.org/10.5194/egusphere-egu25-8342, 2025.
Permafrost degradation is expected to release large amounts of greenhouse gasses to the atmosphere, creating positive feedback to climate warming. The greenhouse balance is largely dominated by microbial decomposition of soil organic matter, however, as permafrost thaws the vegetation composition and growth rate changes and increases the potential to fix carbon in the ecosystem. The aspect of vegetation change, therefore, is worth noting independent of greenhouse emissions from soils under permafrost thawing and climate warming. We investigate how vegetation properties change with permafrost thawing and artificial warming at a natural gradient of permafrost thawing and natural succession and using open top chambers following the International Tundra Experiment (ITEX) protocol at a permafrost affected peatland palsa-mire ecosystem in northern Norway undergoing rapid permafrost degradation followed by natural succession knowns as the Iškoras site. The permafrost affected peat plateau called ‘palsa’ is dominated by evergreen dwarf shrubs such as Empetrum nigrum. As permafrost thaws and palsa collapses, the wet soil conditions promote vegetation shift from E. nigrum to more hydrophilic deciduous shrubs such as Rubus chamaemorus. Eventually, the waterlogged mires will undergo natural succession dominated by non-vascular vegetation such as mosses and lichen as well as sedges. This vegetation transition corresponds to a shift in functional traits from conservative to resource acquisitive. Warming primarily led to an increase in size related traits. Furthermore, vegetation greenness (NDVI) showed a different development over the growing season in response to permafrost thaw and warming. The total biomass and composition have high implications for understanding ecosystem carbon balance as well as CH4 emissions in this ecosystem under rapid permafrost degradation.
How to cite: Lee, H., Althuizen, I., Christiansen, C., and Westermann, S.: Changes in vegetation properties in permafrost affected peatland ecosystem in northern Norway undergoing rapid permafrost degradation, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18164, https://doi.org/10.5194/egusphere-egu25-18164, 2025.
Much of the organic-rich permafrost deposits in the Arctic lie in riverine floodplains where thaw due to polar amplification of climate change has accelerated bank erosion, leaving permafrost carbon deposits vulnerable to degradation by microorganisms. As sediments harbored in the riverbank erode, they are subjected to sediment transport processes, interact with the water column, and are eventually re-deposited in barforms on an opposing riverbank and incorporated to build new land with ensuing forest succession. Using a space-for-time substitution across these deposits and a suite of culture-independent amplicon and shotgun metagenomic sequencing of samples with ages from modern to several thousand years old collected from the Yukon River and its major tributary the Koyukuk River, we set out to understand microbial community succession associated with this process, and connect this with rates of carbon cycling in the subsurface. Because dioxygen is a special molecule concerning the fate of organic carbon in soils and sediments, we also developed a useful ’sequencing-as-sensing’ approach that leverages recent developments in protein language models to assess the time-integrated fraction of the microbial community capable of aerobic biology and oxidative attack of extracellular organic matter. Results revealed that permafrost deposits operate as a ‘seed bank’ that generates a pattern of succession toward an aerobic community capable of rapid carbon degradation during erosion and transport—a pattern that may help explain why carbon burial in river floodplains is so efficacious.
How to cite: Fischer, W., Huy, K., Magyar, J., Richter, P., Flamholz, A., Bar-On, Y., Anadu, J., Ke, Y., Geyman, E., Lamb, M., Mutter, E., Smith, I., and West, J.: Microbial community dynamics following riverbank erosion across permafrost floodplains in the Yukon River basin, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-20717, https://doi.org/10.5194/egusphere-egu25-20717, 2025.
