To meet the Paris Agreement temperature goal, allowable carbon emissions in the future are tightly limited. It is very likely that the 1.5°C temperature limit will be at least temporarily exceeded (overshoot) under an emission pathway following current climate policies and actions. Peatlands store large amounts of soil carbon, the destabilization of which could potentially cause large amplifying feedback on global warming. Using the reduced-complexity Earth system model OSCAR v3.1.2 and a new peat carbon module, we assessed whether carbon emissions from northern peatlands triggered by climate change will increase the chance and intensity of temperature overshoot. We found that, although northern peatlands continue to accumulate carbon, they represent positive feedback under climate change through their high CH₄ emissions. For a 1°C increase in peak temperature anomaly, emissions from peatlands further contribute to the peak temperature by 0.02 (0.01-0.02) °C. Considering northern peatlands would lead to a reduction in the carbon budget by about 40 (16-60) GtCO₂, or 8.6% for 1.5°C, and a reduction of about 105 (45-166) GtCO₂ reduction (or 4.2% relative decrease) for 2.5°C. Our findings highlight the importance of properly accounting for northern peatland emissions for estimating climate feedbacks, especially under overshoot scenarios.

How to cite: Zhu, B., Qiu, C., Gasser, T., Ciais, P., and Lamboll, R. D.: Warming of Northern Peatlands Increases the Global Temperature Overshoot Challenge, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17896, https://doi.org/10.5194/egusphere-egu24-17896, 2024.

Peatlands are essential for providing crucial ecosystem services such as carbon sequestration, water regulation, and biodiversity conservation. However, in Ireland, these vital ecosystems have undergone significant degradation due to practices like land use alterations, drainage, and peat extraction activities. The collective impact of these disturbances, amplified by the influence of climate change, presents a substantial threat to the resilience of Irish peatlands. Here we evaluate the impact of climate gradients on Irish Peatland Resilience at a national scale through the application of a mechanistic model. We identify critical tipping points that signify shifts between peatlands and forests and assess how these vary with climate, and how these impact ecosystem carbon stores. Through  this approach we delineated various peatland types prevalent in Ireland, such as western blanket bogs, mountain blanket bogs, and raised bogs. Furthermore, model outputs were used to derive the resilience index for these diverse peatland systems, providing an indication of their capacity to withstand environmental changes. The insights from this research offer valuable guidance to help target national peatland restoration strategies. Ultimately, this study contributes to the broader goal of sustainable peatland management and preservation amidst changing environmental conditions.

How to cite: Sabokrouhiyeh, N., Van der Velde, Y., Connolly, J., and Kettridge, N.: Irish Peatland Resilience and Presence Across National Climate Gradients , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5786, https://doi.org/10.5194/egusphere-egu24-5786, 2024.

Northern peatlands act as a global carbon sink. At the same time, they are a major source of methane. Rising temperatures due to global warming may severely change carbon dynamics. However, long-term studies to evaluate the impact of global warming on northern peatland ecosystems are rare. Here, we monitored carbon dioxide (CO2) and methane (CH4) dynamics at a subarctic/boreal fen in northern Finland throughout 13 years (2007-2019) using the eddy covariance technique accompanied by measurements of abiotic and biotic drivers. Mean yearly CH4 and CO2 exchange were +21.7 g CH4 and –0.14 kg CO2, respectively. The peatland was an average sink of carbon, with a mean annual uptake of –21.4 g C. It remained also a sink during the exceptionally warm summer of 2018 (–52.3 g C y^-1). Soil temperatures strongly drove CH4 emissions whereby summer soil temperatures governed the annual budget (p < 0.001) and summer emissions determined the annual budget (45-57%, p < 0.001). Observed warming in late summer (+2.1 °C, 2007-2019) did not increase CH4 emissions as soil temperatures remained unchanged. Air and soil temperatures during the growing season and the number of snow-free days controlled annual net CO2 exchange (p=0.003). We found an increasing trend in respiration and primary production in the late growing season, keeping net CO2 exchange equally. Warmer temperatures in the late growing season increased respiration, however, primary production responded only positively to warmer temperatures in spring. Instead, warmer late summers and longer extended autumn growing seasons likely delayed autumn senescence and increased greenness, keeping primary production high. Our results suggest that with ongoing global warming and rising summer soil temperatures, methane emissions from boreal peatlands will further increase, feedbacking on the climate through its high global warming potential. The carbon sink potential will be determined by the number of snow-free days and growing season temperatures. Vegetation changes in the late growing season may offset higher respiration due to warming.  

How to cite: Kübert, A., Aurela, M., Hatakka, J., Laurila, T., Linkosalmi, M., Rainne, J., Tuovinen, J.-P., Vekuri, H., and Lohila, A.: Peatland carbon dynamics in a changing climate: A 13-year flux time series of a fen in Northern Finland , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5132, https://doi.org/10.5194/egusphere-egu24-5132, 2024.

Northern peatlands are recognised as important long-term carbon sinks. However, measurements from a number of peatland sites reveal a large amount of interannual variability in their net carbon dioxide (CO₂) balance. Differences in both weather conditions and plant phenology (i.e. the seasonal development of the vegetation canopy) between years are thought to be key here. Timing of the growing season (i.e. start, end, length) regulates the period over which vegetation can actively photosynthesise. Hence, a longer growing season is often related to increased seasonal CO₂ uptake for example. At the same time, meteorological conditions (e.g. air temperature, water-table depth) affect not only plant physiology, but also its phenological cycle. Our current understanding of the complex interplay between these two main drivers of peatland carbon dynamics has been limited by a lack of long-term phenology studies. This work explores a unique, decade-long record of phenocam and eddy-covariance data from Degerö Stormyr, a northern Swedish peatland. We used structural equation modelling (SEM) to identify the pathways regulating CO₂ uptake, and found that phenology plays an important ‘mediator’ role over the growing season. Our analysis of the interannual and seasonal variability in the drivers of CO₂ uptake further suggest that increases in vegetation greenness are linked to increased CO₂ uptake over the growing season. These findings provide valuable insight on the controls of peatland carbon dynamics, and its feedbacks with future climate change.

How to cite: Simpson, G., Järveoja, J., Nilsson, M., and Peichl, M.: Phenology controls on CO2 exchange in a northern peatland: insights from a decade-long record of phenocam imagery and eddy-covariance data, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14977, https://doi.org/10.5194/egusphere-egu24-14977, 2024.

Arctic wetlands have been identified as significant emitters of CH₄, accounting for about 2% of the global methane budget, but the underlying processes remain poorly constrained. These wetlands show not only a considerable variability in CH₄ flux estimates, but also varying levels of emissions between different regions and even among various elements within the same wetland. The pronounced spatial variability in ecosystem characteristics across scales requires observational approaches that can cover larger landscapes while still being capable of resolving fine-scale details.

This study presents findings based on flux chamber measurements with a portable gas greenhouse analyser for CH4/CO2/H2O (LI-7810), conducted at the Trail Valley Creek research station in the Canadian NW Territories. We collected data from two polygonal mires and a small gulley, all plots organized as transects across moisture gradients. Our approach included analysing variations in CH₄ fluxes across microsites within wetland complexes, such as rims, trenches, or polygon centres. In addition to greenhouse gas signals, we examined soil parameters (pH, temperature, moisture) and vegetation (height, composition, green fraction) to understand their influence on CH₄ fluxes. Random forest models highlighted soil moisture at 12 cm as a primary control factor, explaining 41% of the predictive power and demonstrating higher accuracy compared to linear models for CH₄ flux prediction. Based on partial dependence analyses, we classified our measurements into three groups based on soil moisture at 12 cm. In the low moisture scenario, soil moisture at deeper levels (30 cm) was more influential, while in medium moisture conditions, soil temperature at 10 and 20 cm depths played a crucial role. In the high moisture category, the presence of Carex aquatilis was a key factor influencing the CH₄ flux. 

Our study also showed that the CH₄ flux varied significantly among different wetland elements. The gully area showed the lowest rate, whereas the polygonal mires had higher fluxes. Notably, within a polygonal mire, the rim exhibited lower flux compared to the wet polygonal centres and trenches, the latter showing the highest emissions. These findings underscore the complexity and variability of CH₄ fluxes in Arctic wetland ecosystems and highlight the importance of considering both soil and vegetation characteristics in understanding and predicting CH₄ emissions from these critical regions.

The authors acknowledge funding from the European Research Council (ERC synergy project Q-Arctic, grant agreement no. 951288).

How to cite: Ivanova, K., Goeckede, M., Vogt, J., and Kuechenmeister, A.: Impact of soil and vegetation characteristics on CH4 fluxes in Arctic wetlands of the Northwest Territories, Canada , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6460, https://doi.org/10.5194/egusphere-egu24-6460, 2024.

Draining peatlands results in oxic soil conditions that causes microbial oxidation of peat. Drained peatlands are a large source for CO₂ emissions, contributing 2-5% to the total anthropogenic greenhouse gas emissions. Understanding processes that contribute to peat oxidation are useful to simulate, predict and project CO₂ emission in different environmental conditions. In wet conditions, soil is anoxic, which leads to an increase in methane (CH₄) emission. Wetlands, including peatlands, are the largest natural source of CH₄. Weather conditions, water table height, substrate availability, and vegetation type play a crucial role in the amount of CH₄ that is emitted. The dynamic of CH₄ production and oxidation, driven by the above mentioned factors, is complex. Nevertheless, for both CO₂ and CH₄, it is essential to be able to simulate these fluxes with a mechanistical model for monitoring and predicting greenhouse gas emission from peatlands.

PEATLAND-VU is a 1D process based model, consisting of four submodels for 1) soil physics (water table, soil temperature and soil moisture), 2) biomass production, 3) CH₄ production, oxidation and transport (diffusion, ebullition and plant transport), and 4) CO₂ production. Here, CO₂ production is represented as the sum of decomposition from different soil organic matter (SOM) pools, like litter, root exudates, microbial biomass, and peat.

We calibrated the PEATLAND-VU model for two intensively used drained peat meadows and a wet Sphagnum-reed peatland in the Netherlands. These sites have 2-4 years of CO₂ flux and CH₄ flux (Sphagnum-reed peatland only) data. In our presentation we will show that the model performed well for simulating CO₂ and CH₄ fluxes. We will focus on the contribution of peat oxidation to the total CO₂ emission, and show results of different water table management and future climate scenarios. Furthermore, for the Sphagnum-reed peatland the modelled CH₄ production, CH₄ oxidation, and the transport pathways resulting in the net CH₄ flux will be discussed.

How to cite: van den Berg, M., van Huissteden, J., Lippmann, T. T. R., Boonman, J., Buzacott, A. J. V., and van der Velde, Y.: Modelling CO2 and CH4 fluxes from drained and natural peatlands with the PEATLAND-VU model, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18513, https://doi.org/10.5194/egusphere-egu24-18513, 2024.

We measured CO₂ and CH₄ fluxes using chambers and eddy covariance (only CO₂) from a moist moss tundra in Svalbard. The average net ecosystem exchange (NEE) during the summer (9 June-31 August) was negative (sink) with -0.139±0.032 µmol m^-2s^-1 corresponding to -11.8 g C m^-2 for the whole summer. The cumulated NEE over the whole growing season (day no. 160 to 284) was -2.5 g C m^-2. The CH₄ flux during the summer period showed a large spatial and temporal variability. The mean value of all 214 samples was 0.000511±0.000315 µmol m^-2s^-1 which corresponds to a growing season estimate of 0.04 to 0.16 g CH₄ m^-2. Thus, we find that this moss tundra ecosystem is closely in balance with the atmosphere during growing season when regarding exchanges of  CO₂ and CH₄. The sink of CO₂ as well as the source of CH₄ are small in comparison with other tundra ecosystems in high Arctic.

Air temperature, soil moisture and greenness index contributed significantly to explain the variation in ecosystem respiration (R_eco) while active layer depth, soil moisture and greenness index were the variables that best explained CH₄ emissions. Estimate of temperature sensitivity of R_eco and gross primary productivity (GPP) showed that the sensitivity is slightly higher for GPP than for R_eco in the interval 0 – 4.5 ºC, thereafter the difference is small up to about 6 ºC and then it began to raise rapidly for R_eco. The consequence of this, for a small increase in air temperature of 1 degree (all other variables assumed unchanged) was that the respiration increased more than photosynthesis turning the small sink into a small source (4.5 gC m^-2) during the growing season. Thus, we cannot rule out that the reason why the moss tundra is close to balance today is an effect of the warming that has already taken place in Svalbard.

How to cite: Lindroth, A., Pirk, N., Jonsdottir, I., Stiegler, C., Klemedtsson, L., and Nilsson, M.: CO2 and CH4 exchanges between moist moss tundra and atmosphere on Kapp Linne, Svalbard, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18409, https://doi.org/10.5194/egusphere-egu24-18409, 2024.

Northern peatlands are significant carbon reservoirs, serving as long-term atmospheric carbon dioxide sinks and sources of methane and nitrogen dioxide. However, methane processes interacting with environmental changes in Northern peatlands, remain unclear. Therefore, the need for better simulation of key processes of methane in peatlands is still urgent. In this study we used the process-based CoupModel combining the long-term in-situ measurements to successfully constrain the energy, water and carbon fluxes modeling in a boreal peatland (CH4, r²=0.62). We noticed that plant transportation is the most dominant pathway for methane emissions from this peatland (57.87% of total CH4 emission), followed by surface diffusion (31.06%) and ebullition (11.07%). The relationship between CH4 fluxes and water table depth is non-linear, and the dominant CH4 emission pathway varies as the water table regime changes. Our study provided new insights into the emission mechanisms of methane in boreal minerotrophic mire and contributed to a better understanding of boreal peatlands for both modelling and observation communities.

How to cite: Wu, M., Duan, W., Noumonvi, K., Ratcliffe, J., Nilsson, M., Peichl, M., and Jansson, P.-E.: Modelling the northern peatland methane fluxes with a process-based model, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9601, https://doi.org/10.5194/egusphere-egu24-9601, 2024.

Canada’s peatlands hold more than half of the organic carbon stocks stored in all Canadian soils. Over 90% of these peatlands are in the boreal and subarctic regions that are undergoing accelerated climate warming. Climate models project that the rate of warming will continue through the 21^st century, with the greatest warming occurring during the non-growing season (NGS). Given that NGS carbon dioxide (CO₂) emissions are mainly driven by microbial respiration, warming, even at sub-zero temperatures, is expected to increase the CO₂ emissions during the NGS. Therefore, understanding the factors that regulate CO₂ emissions during the NGS is critical for predicting the fate of the climate-sensitive peat organic carbon stocks. In this presentation, we examine the role of environmental variables in NGS CO₂ emissions at a Canadian peatland research site to infer how these emissions may evolve under climate warming scenarios. We developed a support-vector regression machine-learning model whose results imply that soil moisture, soil temperature, snow cover, and photosynthesis are key predictor variables explaining the variability of net ecosystem CO₂ fluxes during the NGS. The model was applied to a 13-year (1998-2010) continuous record of eddy covariance flux measurements at the Mer Bleue Bog (located near Ottawa, Canada). The CO₂ fluxes were most sensitive to the net radiation above the canopy, wind speed, soil temperature, and soil moisture. Next, we used regional climate projections for the site to forecast future changes in the net ecosystem exchange of CO₂ during the NGS. Under the highest radiative forcing scenario, the NGS Mer Bleue peatland CO₂ emission rates could experience a 103% increase by 2100. Time permitting, we will also discuss results from a laboratory incubation CO₂ experiment with soils from Canadian boreal and temperate peatlands under variable moisture and temperature conditions. The incubation temperature ranged from −10 to +35°C and included freeze–thaw events. The results showed that CO₂ production rates increased more sharply with temperature for the boreal peatland soils than the temperate ones. This indicates that boreal peatlands may increase future NGS CO₂ losses to a larger degree than temperate peatlands. Our results thus further highlight the potential for a strong positive climate feedback loop from accelerated peatland CO₂ emissions. They also point to the need for more realistic representations of northern soil processes in earth system models.

How to cite: Rezanezhad, F., Rafat, A., Byun, E., Slowinski, S., Hettinga, K., Saraswati, S., Persaud, B., Quinton, W. L., Humphreys, E. R., Webster, K., Liu, H., Lennartz, B., Strack, M., and Van Cappellen, P.: How will climate warming impact winter CO2 emissions from northern peatlands?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5924, https://doi.org/10.5194/egusphere-egu24-5924, 2024.

Peatlands store about one-third of global soil organic carbon. The carbon dynamics and storage of peatlands depend on the balance between plants’ carbon uptake and microbial carbon decomposition. As a result of global warming and climate-driven ecohydrological changes, the plant community composition of peatlands is projected to change, affecting the carbon sequestration and storage capacity of these ecosystems both directly and indirectly by modulating water flows. However, while there has been a notable focus on studying the variation in the water table position of peatlands and its consequential influence on the dynamics of peatland soil carbon, the impacts of peatland plant community composition have been largely overlooked. To accurately predict peatland carbon dynamics, land surface models need to account for the diversity of peatlands plant types and the competitive interactions among them. We incorporated six plant functional types (PFT) into the ORCHIDEE-PEAT model to represent mosses, grasses, shrubs, and trees growing in peatlands. Areas covered by each PFT are functions of the bioclimatic limitations, mortality, and establishment of each PFT, as well as competitions among PFTs. The model will be employed to assess the effect of climate change on peatland vegetation dynamics and carbon fluxes.

How to cite: Qiu, C. and Ciais, P.: Modelling sub-grid peatland vegetation dynamics in the ORCHIDEE-PEAT land surface model, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7100, https://doi.org/10.5194/egusphere-egu24-7100, 2024.

Peatlands are an important global carbon (C) reservoir storing at least one-third of global soil organic carbon (SOC), but little is known about the stability of these vast C stocks under climate change. Here, we examine the impact of four years of warming (+0, +2.25, +4.5, +6.75, +9 °C) and two years of elevated atmospheric CO₂ concentration (eCO₂) on the molecular composition of SOC to infer SOC sources (microbe-, plant- and fire-derived) and stability in a boreal peatland. We show that while warming alone decreased plant- and microbe-derived SOC due to enhanced decomposition, warming combined with eCO₂ increased plant-derived SOC compounds. Further, using biopolymers distinct to either leaf/needle (cutin) or root (suberin), we observed increasing root-derived inputs and declining leaf-derived C inputs into SOC under warming and eCO₂. Unsurprisingly, SOC derived from historical pyrolysis (pyrogenic C) was unaffected by warming or eCO₂. The decline in SOC compounds with warming and gains from new root-derived C under eCO₂, suggest that warming and eCO₂ may shift peatland C budget towards pools with faster turnover. Together, our results indicate that climate change may increase inputs and enhance decomposition of SOC potentially destabilising C storage in peatlands.

How to cite: Nicholas, O., Michael, S., Samuel, A., Paul, H., Colleen, I., Rachel, W., Joel, K., Guido, W., and Avni, M.: Climate warming and elevated CO2 alter peatland soil carbon sources and stability , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5368, https://doi.org/10.5194/egusphere-egu24-5368, 2024.

Temperate swamps hold substantial carbon (C) in their standing biomass and can potentially accumulate peat. In Southern Ontario, Canada, swamp peats are estimated to store ~1.1 Pg C, with this C accumulation supported by distinct hydroclimatic conditions. Previous studies on swamps C fluxes are mostly based on short-term (<5 years) field measurements that limit our understanding of the long-term (>30 years) interactions and feedbacks that exist between temperate swamp C flux and biophysical conditions. In this study, we adopted a process-based model (CoupModel, www.coupmodel.com) to simulate daily plant processes, energy, water, and C fluxes in one of the most well-preserved swamps in Southern Ontario, Beverly Swamp, over a 40-year period (1983-2023). CoupModel reproduced the measured C flux and controlling variables with (coefficient of determination, R²) values of 0.75, 0.94 & 0.6 for soil respiration, surface soil temperature (0-5 cm) and water table depth, respectively. Analysis of the interrelationships (R² values) between the simulated carbon flux and biophysical conditions showed that 88%, 51%, 31%, 68% of soil respiration rates were explained by soil surface temperature, soil volumetric moisture contents (0-30 cm), water table depth and gross primary productivity, respectively.  Our model simulation showed the swamp’s C uptake capacity, as net ecosystem exchange, dwindled over the simulated period but it was a net C sink in most years. This decreasing trend can be attributed to warmer and drier conditions in the region, which may be exacerbated with future climate change predictions. Overall, the study shows that processed-based models (CoupModel) are effective tools for improving our understanding of long-term C dynamics of temperate forested wetlands and the interactions that exist between C flux components and abiotic conditions. This has implications for informed decision-making on the management of temperate swamp ecosystems and the C stored within them.

How to cite: Afolabi, O., He, H., and Strack, M.: Process-based modelling of long-term carbon dynamics in a temperate swamp peatland, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4204, https://doi.org/10.5194/egusphere-egu24-4204, 2024.

We analyzed 10 years (2013-2022) of CO₂ and CH₄ flux data measured using the eddy covariance method in the Biebrza National Park in north-eastern Poland. The Biebrza wetlands are among the largest in Central Europe, comprising a contiguous area of more than 250 km².  The measurement site (53°35′30.8′′ N, 22°53′32.4′′ E, 109 m a.s.l.) was located in the central basin of Biebrza valley at the area dominated by patches of reeds, high sedges, and rushes, very typical of Biebrza wetlands. In the analyzed period the studied ecosystem was affected by severe droughts in 2015 and 2018-2020. Moreover, on April 20–25, 2020, the Biebrza National Park was touched by huge fires that consumed over 5,500 ha of landscape. The measurement site was located at the north-eastern edge of the burned area and the entire source area of eddy-covariance system was affected by the fire. The system suffered some damage, but flux measurements were re-established about a week after the fire. 

The response of the CH₄ flux to changes in hydrometeorological conditions is quite simple - the thermally determined annual course of CH₄ is strongly modified by the water table level (WTL). The annual emission of CH₄ reached 21 gC-CH₄·m^-2·yr^-1 in the wettest year and dropped even below 1 gC-CH₄·m^-2·yr^-1 in dry years. The CO₂ exchange response is more complex. In the case of net ecosystem exchange (NEE), a linear relationship is observed between the average WTL and the annual sum of CO₂ flux. In wet years the studied peatland was a significant sink of CO₂ (down to −250 gC-CO₂·m^-2·yr^-1) whereas in dry years we observed a substantial release of CO₂ (up to +300 gC-CO₂·m^-2·yr^-1). A similar linear relation was observed for ecosystem respiration (ER), which ranged from 830 to 1400 gC-CO₂·m^-2·yr^-1 in wet and dry years respectively. In contrast, gross ecosystem production (GEP) followed WTL changes only in the first 3 years of observations. Vegetation then switched to drier conditions and GEP remained on similar level up to 2020, when it increased significantly after the April fire. Excluding 2020, GEP varied in the range of 910-1250 gC-CO₂·m^-2·yr^-1.

Acknowledgements: Funding for this research was provided by the National Science Centre, Poland under project UMO-2020/37/B/ST10/01219 and University of Lodz under project 4/IDUB/DOS/2021. The authors thank the authorities of the Biebrza National Park for allowing the continuous measurements in the area of the Park.

How to cite: Fortuniak, K., Pawlak, W., Siedlecki, M., and Górowski, J.: The impact of wildfire and droughts on the GHGs exchange in temperate wetland., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6668, https://doi.org/10.5194/egusphere-egu24-6668, 2024.

Rising air temperatures are leading to both an increase in frequency of freeze-thaw cycles (FTCs) during the winter months, and increased fire frequency and severity during the growing season in northern temperate peatlands. Both FTCs and fires have been shown to impact plant and microbial community composition, nutrient availability, and plant-microbe interactions. Ultimately such changes may affect carbon cycling in peatlands. While examples from the vegetation are numerous, no study has assessed the resilience of peatland microbial communities and carbon cycling to the combined disturbance effect of fire and FTCs. The objectives of this study were to (a) determine how peatland microbial community structure and activity are affected following fire, and (b) assess if the impact of FTCs on peatland microbial communities and soil carbon stores is affected by fire history. To address these objectives, we conducted an FTC and incubation experiment using surface peat (2 – 15 cm) from a pristine peatland and nearby peatland that burned in 2006 located in southern Sweden. Peat from both sites was exposed to 15 FTCs, with each FTC consisting of 18 hours at -20 °C followed by 6 hours at +20 °C. Following the termination of the FTCs we incubated the peat at +20 °C for 40 days, measuring peat respiration as the change in headspace greenhouse gases throughout. We measured peat pore water chemistry, hydrolytic enzyme kinetics, and microbial community assembly using metagenomics before and after the FTCs and incubation. Extracellular enzyme kinetics and pore water chemistry data suggest a legacy effect of the fire, whereby the pristine site exhibits greater enzyme degradation and greater lability of dissolved organic matter before and after FTCs. We also saw greater rates of respiration in peat from the pristine site. We found that FTCs in fire affected peat caused an increase of dissolved organic carbon and aromatic compounds in peat pore water, leading to a reduction in extracellular enzyme and respiration rates. We conclude that while FTCs have the potential to disrupt the stability of peatlands, the legacy of fire exerts a greater constrains on biogeochemical processes. This project highlights that growing season disturbances may have a longer lasting impact on peatland resilience.

How to cite: Heffernan, L., Peacock, M., Mehrshad, M., Papadopoulou, S., Robroek, B. J. M., and Davidson, S. J.: Compounding effect of fire history and freeze thaw cycles on ecosystem resilience in northern temperate peatlands, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11533, https://doi.org/10.5194/egusphere-egu24-11533, 2024.

Temperate peatlands and heathlands are at increasing risk of severe wildfires under future climates which may combust legacy carbon stocks. The moisture content of the different fuel layers determines the threat posed. The controls on fuel moisture and their response to extreme weather have previously been unknown. Here, we show that controls differ between fuel layers. Fine dead fuel moisture is dominated by weather, live fuel by temporal controls including season and phenology, and soil organics by elevation and soil type. This separation of controls in time and space produces a landscape resistance to severe wildfire. However, extreme weather events break the phenological control on live fuel moisture and the landscape control of organics, resulting in low moisture content across all fuel types. This leads to the most severe conditions for fire ignition, spread and impact in traditionally non-fire prone regions, producing a landscape susceptible to severe environmental impacts and carbon emissions within a new summer wildfire regime.

How to cite: Ivison, K., Little, K., Graham, L., and Kettridge, N.: Extreme weather breaks phenological and landscape controls on temperate peatland fuel moisture; implications for carbon stock release through changing wildfire regimes, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11396, https://doi.org/10.5194/egusphere-egu24-11396, 2024.

Peatlands play an essential role for the global climate, providing a large storage of carbon (C) and the largest natural source of methane (CH₄). Previous studies revealed that carbon dioxide (CO₂) flux varies at the seasonal scale depending on plant phenology and species compositions. In addition to the C sink-strength, allocation of newly assimilated C is another important process to estimate C pool size and turnover, and also a key to understand the connection between plant-assimilated CO₂ and CH₄ emissions. To date, seasonal variations in the link between plant CO₂ uptake and CH₄ emissions in response to phenology have not been investigated in detail.

To reveal diurnal and seasonal dynamics of CO₂ and CH₄ flux with a high temporal resolution, we used data from an automated chamber system established in an oligotrophic minerogenic mire complex in northern Sweden (Degerö Stormyr). To identify the role of plant species composition, experimental plots without vascular plants (moss plots) and without any vegetation (bare peat plots for assessing heterotrophic respiration) were established next to the natural control plots. We conducted two in-situ ¹³C pulse labelling experiments at two distinct phenology stages (green-up and senescence) during 2023. The fate of the newly assimilated ¹³C was tracked through the entire C flow from plants (vascular plants and mosses), to dissolved organic and inorganic ¹³C in pore water, to ¹³CO₂ and ¹³CH₄ flux. The main objectives were to investigate 1) seasonal variations in the C allocation pattern and turnover time, and 2) the separate roles of vascular plants and mosses in regulating C allocation dynamics.

Our results indicate that in the green-up stage, both natural and moss plots released around 20% of the total newly assimilated ¹³C as CO₂ flux during the 30 days after the labelling. In the senescence stage, the amount in the moss plots increased to 26 ± 3%, while that of natural plots remained at 20%. In comparison, release of newly assimilated C as CH₄ did not show any seasonal variations in neither natural nor moss plots, highlighting a close link between plant C uptake and CH₄ emission. However, existence of vascular plants increased the proportional release as CH₄ emission tenfold from 0-0.02% of total ¹³C uptake in moss plots to 0.1-0.2% in natural plots.

These results highlight the importance of plant species composition and phenology in regulating the allocation of assimilated carbon in northern peatlands.

How to cite: Hikino, K., Hartmann, A., Öquist, M., Järveoja, J., Nilsson, M., and Peichl, M.: Seasonal dynamics in the allocation of newly assimilated carbon in a northern peatland, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5174, https://doi.org/10.5194/egusphere-egu24-5174, 2024.

To study long-term impacts of nutrient addition on carbon sequestration capacity, we investigated changes in vegetation and ecosystem CO₂ exchange at Mer Bleue Bog, Canada in plots that had been fertilized with nitrogen (N) or with N plus phosphorus (P) and potassium (K) and in non-fertilized control plots for 13-18 years. The vegetation structure and species composition were measured in all treatments mid July 2001-2018 (14 measurement years) using a point intercept method. Gross photosynthesis, ecosystem respiration, and net CO₂ exchange were measured weekly during June–August 2001-2016 (7 measurement years, usually every two years) using climate-controlled chambers. Using Bayesian approach, we analyzed whether there were changes over time in vegetation and ecosystem CO₂ exchange and whether those trends differed between treatments. We found that shrubs had become taller and more abundant at the unfertilized plots during the 18 study years likely owing to warmer summers and a drying trend that favor shrubs. At the fertilized plots, the increase in shrub height was greater and faster than in unfertilized plots, and the addition of PK with N further accelerated growth of the shrub canopy. Among the dwarf shrubs, only Chamaedaphne calyculata benefitted from the fertilization. No change towards more gramineous vegetation was observed. Because the plants at the bog are N-P co-limited rather than N-limited, PK addition alleviated growth limitation. Sphagnum cover decreased with the increasing nutrient load. Ecosystem respiration increased in all treatments, but it increased faster and more in fertilized plots than in unfertilized plots. In all treatments, increases in ecosystem respiration resulted in less net CO₂ uptake during the recent ten years (since 2008), because gross photosynthesis rates did not compensate for increases in ecosystem respiration. In general, the magnitude of this trend of reduced net C sink potential did not differ markedly in unfertilized from fertilized plots. These CO₂ flux trends could be explained by changes in nutrient availability, a larger proportion of nongreen biomass in dense stands and enhanced peat decomposition. Our long-term field experiment revealed that ecosystem responses to the combination of nutrient addition and drying must be considered when evaluating the impact of climate change on the carbon sink potential of peatlands.

How to cite: Larmola, T., Bubier, J., Liski, E., Kostensalo, J., Moore, T., Antila, J., Humphreys, E., and Juutinen, S.: Long-term changes and impacts of nutrient addition to vegetation and CO2 fluxes at ombrotrophic Mer Bleue Bog, Canada, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4287, https://doi.org/10.5194/egusphere-egu24-4287, 2024.

Permafrost peatlands, primarily occurring at northern latitudes, are a major stock of organic carbon. Although these peatlands have historically acted as a carbon sink, they are expected to transition to a carbon source due to the mobilization and rapid decomposition of accumulated organic carbon by microorganisms upon thawing. Predictions of the timescale of this transition are limited by insufficient understanding of the controls on organic carbon decomposition. One major control on microbially mediated decomposition and release of greenhouse gases carbon dioxide (CO₂) and methane (CH₄) is the interaction of organic carbon with minerals (predominantly high surface area iron minerals). Although well studied in common soil systems, the role of organic carbon-mineral interactions in carbon cycling is poorly understood in permafrost peatlands. This knowledge gap is particularly critical in the case of permafrost thaw, during which redox conditions may switch from oxic to anoxic due to extensive waterlogging.

            In this work, we investigated the interaction between organic carbon and minerals and their effect on carbon cycling in thawing permafrost peatlands. We chose Stordalen mire near Abisko, Sweden, as a representative field site as it includes a thaw gradient from intact permafrost plateaus to thaw ponds and fully thawed wetlands. Specifically, we investigated whether interaction with iron minerals protected organic carbon from microbial decomposition and release as CO₂ and CH₄ over thaw in field manipulation and laboratory microcosm experiments. To do this, we synthesized iron mineral-organic carbon phases using organic matter from the peatlands and added them to the soil. We then followed dissolved organic carbon dynamics as well as CO₂ and CH₄ release. In addition, we tracked the fate of the minerals over thaw. In a complementary study, we characterized mineral-organic carbon phases present within the soil and thaw ponds. Upon addition of the mineral-organic carbon phases to the soil, we observed a small decrease in greenhouse gas release over the short term, consistent with the results from other soil systems. However, over the timescale of weeks, the greenhouse gas release increased substantially relative to control experiments, especially in the case of CO₂ (up to 130%). This increase could be attributed to the use of iron within the mineral-organic carbon phases as an electron acceptor by microorganisms, promoting organic carbon decomposition. The results of this work suggest that (a) iron mineral-associated organic carbon in permafrost peatlands may not be protected from microbial decomposition, and (b) increased water levels in permafrost peatlands due to thaw may result in increased greenhouse gas release, particularly CO₂.

How to cite: Joshi, P., Chauhan, A., Voggenreiter, E., Wunsch, K., and Kappler, A.: Role of mineral-organic matter interactions in carbon cycling in permafrost peatlands, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5008, https://doi.org/10.5194/egusphere-egu24-5008, 2024.

Permafrost-affected peatlands are hotspots globally because of their large carbon storage and climate sensitivity. However, there have been limited studies on the abundance and controlling factors of iron-associated organic carbon (Fe-OC) in these important ecosystems. Here we conducted a large-scale comparison study of soils across major terrestrial ecosystems—including croplands, forest, grasslands, wetlands and peatlands—to understand differences in the distribution of Fe-OC abundance. Our results show that the Fe-OC abundance of peatlands (13.3±9.6 g kg^-1) are higher than that in non-peat forming wetlands (6.4±4.5 g kg^-1) and mineral soils, such as croplands (9.1±9.3 g kg^-1), forest (10.5±11.1 g kg^-1) and grasslands (2.0±2.2 g kg^-1), implying the efficient binding capacity of iron minerals with OC in peatlands. Further, our field and laboratory investigations focus on Northeast China, the major peatland-dominant region in China with permafrost-affected and non-permafrost peatlands—including Sphagnum-dominated bogs and sedge-dominated fens, to clarify the processes and mechanisms of Fe-OC accumulation. We find that permafrost-affected peatlands contain near 5-fold higher Fe-OC than non-permafrost peatlands. Our parallel factor analysis of fluorescence excitation-emission matrix results shows that microbial-derived carbon accounts for 25.5-90.7% of Fe-OC in permafrost peatlands, with an average contribution of 56.0%. Moreover, we observed a positive correlation between the Fe-OC abundance and the proportion of OC derived from microbes. Iron minerals in permafrost peatlands tend to bind a greater proportion of labile carbon—whether derived from plants or microbes—than in non-permafrost peatlands, suggesting that the presence of permafrost offers an important mechanism for climate change mitigation. Furthermore, nutrients (such as nitrate, phosphate and C:N ratio) are major controlling factors for Fe-OC in non-permafrost peatlands (with a total effect of up to 96.9%), while reactive Fe (with an effect of up to 96.9%) and other factors (including pH, climate, FeRB and microbial-derived OC) positively influence Fe-OC in permafrost peatlands. These findings demonstrate that iron minerals act as a crucial ‘OC protectors’ that greatly boost the rusty carbon sink in cryogenic ecosystems. Future climate warming and permafrost thaw will not only reduce low-temperature protection of previously frozen carbon—some of them labile—but also diminish the mineral-association protection of a large quantity of carbon.

How to cite: Yang, L., Jiang, M., Yu, Z., and Zou, Y.: Iron-associated organic carbon as a major carbon sink in permafrost-affected peatlands of Northeast China, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1102, https://doi.org/10.5194/egusphere-egu24-1102, 2024.