This scientific session will focus aims to integrate across the multiple scales of peat carbon oxidation. We will explore:
Microscale Processes: Understanding the role of biogeochemistry and microorganisms in peat decomposition and the processes that determine peat carbon oxidation potentials and rates.
Intermediate-Scale Measurements: Applying techniques and methodologies to measure carbon turnover and emissions, the insights they provide in underlying processes, and techniques for upscaling.
Challenges in Upscaling: Addressing the links between small-scale processes and ecosystem-scale emissions. This includes modeling approaches and integrative methods to connect scales.
Solicited author:
Dominik Zak
Orals: Wed, 6 May, 10:45–12:30 | Room 2.95
Peatlands store a substantial fraction of the global soil carbon pool. Widespread drainage and land-use change have accelerated peat decomposition, while current restoration efforts aim to slow or reverse peat carbon oxidation and associated greenhouse gas emissions through rewetting. Understanding when and to what extent rewetting restores carbon sequestration and long-term peat accumulation remains a key scientific and management challenge.
Over recent decades, substantial progress has been made in identifying the biogeochemical controls on peat carbon turnover in rewetted systems. Water table dynamics, hydrological connectivity, redox conditions, substrate availability, nutrient status, and vegetation composition jointly regulate microbial processes driving organic matter decomposition and carbon fluxes. Yet, key questions remain: what really drives carbon turnover in peatlands? Is it “the overriding role of the water table”, the “iron gate” of mineral interactions, or the “iron wheel”? Could there even be a single enzyme controlling global carbon storage (Wen et al., 2019)? These questions highlight how peat carbon cycling defies simple explanations and directly challenges long-standing paradigms. Classical concepts emphasizing intrinsic substrate recalcitrance, single inhibitory controls (e.g., phenolics or water table position), or strictly separated aerobic–anaerobic microbial pathways fail to capture the complexity of carbon stabilization and turnover observed in rewetted peatlands (Zak et al., 2019). Instead, emerging evidence points to a network of interacting, context-dependent processes, including microbial community turnover, mineral–organic interactions, and dynamic redox condition changes, underpinning peat carbon persistence.
Yet, these mechanisms are typically studied at micro- to plot scales, while restoration success and climate feedbacks are evaluated at ecosystem to landscape scales, posing persistent challenges for upscaling. In this contribution, we synthesize current insights into carbon cycling in rewetted riparian peatlands by explicitly linking microbial and biogeochemical controls on carbon decomposition with restoration approaches aimed at managing carbon fluxes. Emphasis is placed on spatial and temporal heterogeneity in peat properties, hydrology, and microbial functioning, and on how this variability propagates uncertainty in carbon balance assessments and model predictions.
By integrating process-based understanding with measurements and modeling perspectives, both recent advances and remaining knowledge gaps in predicting peat carbon cycling under restoration will be highlighted. Re-assessing prevailing paradigms and strengthening cross-scale linkages are essential for designing effective rewetting strategies.
References
Wen, Y., Zang, H., Ma, Q., Evans, C. D., Chadwick, D. R., & Jones, D. L. (2019). Is the ‘enzyme latch’or ‘iron gate’the key to protecting soil organic carbon in peatlands?. Geoderma, 349, 107-113.
Zak, D., Roth, C., Unger, V., Goldhammer, T., Fenner, N., Freeman, C., & Jurasinski, G. (2019). Unraveling the importance of polyphenols for microbial carbon mineralization in rewetted riparian peatlands. Frontiers in Environmental Science, 7, 147.
How to cite: Zak, D., Jurasinski, G., Christiansen, J., Liebner, S., Petersen, R., Audet, J., Vroom, R., and Hermansen, N.: The complexity of carbon cycling in peatlands: a biogeochemical perspective, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17613, https://doi.org/10.5194/egusphere-egu26-17613, 2026.
Northern peatlands are major carbon sinks, but their response to warming is difficult to predict because carbon uptake depends on complex interactions between climate, vegetation and drainage. We tested whether the composition of dissolved organic matter (DOM) in peat pore water reflects the biogeochemical functioning of the system and, therefore, can predict the carbon sink response to increased temperature. Using 16 peatland mesocosms subjected to contrasting climatic and hydrological conditions, we measured noon-time CO2 exchange and analyzed DOM optical properties. Interaction forest models were used to predict carbon balance from peatland characteristics combined with DOM composition data. The CO2 sink strengthened with warming in mesocosms with low DOM aromaticity, marked by high protein-like and microbially derived fluorescence, but remained weak when DOM was more aromatic. These results show that DOM composition is a sensitive indicator of peatland carbon balance under warming and can improve predictions of future carbon sink behavior.
How to cite: Berggren, M., Salimi, S., Tafazoli, M., and Scholz, M.: Dissolved organic matter composition predicts the carbon sink in a northern peatland warming experiment, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-20511, https://doi.org/10.5194/egusphere-egu26-20511, 2026.
Permafrost peatlands represent a large organic carbon stock and are currently a net carbon sink. However, some permafrost regions will develop anoxic conditions due to soil subsidence and waterlogging in the future. Under these conditions, it is estimated that methane (CH4) emissions will increase due to the higher availability of newly mobilized dissolved organic matter (DOM) for microorganisms. However, little attention has been given to redox-active functional groups within DOM, which could also play a role in lowering CH4 emissions. On the one hand, oxidized redox-active DOM could suppress methanogenesis thermodynamically, while on the other hand it could act as an electron acceptor for anaerobic CH4 oxidation (AOM). Both processes would decrease net CH4 release. However, the change in redox-active moieties in DOM across thaw in permafrost peatlands and their role in AOM have not been determined yet. In this project, we therefore aim (i) to quantify the changes in abundance and oxidation state of redox-active DOM along a thaw gradient and (ii) to determine the effect of oxidized redox-active DOM on AOM. To achieve this, we collected porewater samples over four depths (10-40 cm) across multiple thaw stages during July and September 2025 in a thawing permafrost peatland in Sweden (Stordalen Mire, Abisko). We analyzed the electron accepting and donating capacity of the anoxic porewater via mediated electrochemical reduction and oxidation, respectively. We found that the electron accepting capacity attributable to DOM significantly decreases from recently thawed to fully thawed sites (from 1.68±0.65 to 0.77±0.58 mmol e- g-1 C-1, p<0.01). Further, mean electron donating capacity attributable to DOM was positively correlated to the average CH4 flux per site (R=0.53, p<0.05), suggesting that more reduced redox-active DOM co-occurs with a higher CH4 release. Additionally, microcosm experiments with water-extracted DOM from the peat and 13C-labeled CH4 were performed in order to quantify the rates of methane oxidation in the presence and absence of redox-active DOM. We used a combination of electrochemical, isotope-tracing and molecular biology techniques to track the reduction of amended DOM, production of 13C-CO2 and the change in abundance of methane-oxidizing microorganisms. Overall, this work will help to assess the importance of redox-active DOM for CH4 cycling in thawing permafrost peatlands.
How to cite: Voggenreiter, E., Hahn, Z., Valenzuela, E. I., Hudson, J., Kappler, A., and van Grinsven, S.: Role of redox-active dissolved organic matter for methane cycling in thawing permafrost peatlands, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5304, https://doi.org/10.5194/egusphere-egu26-5304, 2026.
Peatlands are globally important sources and sinks of methane (CH4), yet the extent to which land-use change alters the balance between methanogenesis and methane oxidation across peatland types remains poorly constrained. Here, we quantify potential methane production and aerobic methane oxidation across 27 peatland sites within the EU Biodiversa+ project network, spanning Estonia, Finland, Germany, and Czechia and encompassing pristine, drained, and rewetted bogs and fens.
We combined laboratory incubation assays with molecular approaches to assess methane cycling potential in both the aerobic peat layer and below the water table. Potential CH4 production and oxidation rates were measured under controlled conditions, alongside quantitative PCR targeting methanogenic (mcrA), methanotrophic (pmoA), and total bacterial (16S rRNA) genes. Shotgun metagenomics and 16S rRNA gene sequencing were used to explore the genomic potential for methane oxidation and to identify microbial taxa involved.
Preliminary results indicate that pristine peatlands exhibit the highest potential rates of both methane production and oxidation. Drained sites show strongly reduced methanogenic potential, while rewetted sites display partial recovery, with rates generally remaining lower than in pristine systems. Higher methane oxidation rates in long-term rewetted sites (>15 years) suggest that functional recovery may increase with time since rewetting. When separated by peatland type, bogs show higher methane cycling potentials than fens across all land-use categories.
Pristine peatlands consistently showed highest methanogen gene abundances compared to rewetted and drained, particularly in the anaerobic peat layer. Methanotrophic gene abundances were highest in pristine peatlands in the aerobic layer; however, anaerobic layers of rewetted and drained peatlands harbored higher methanotrophic communities than in their aerobic layers. This suggests that methanotrophic communities in managed peatlands may establish deeper in the peat profile, potentially in response to oxygenic microsites or dynamic redox conditions. In rewetted and drained sites, pmoA gene abundance explained ~20% of the variation in methane oxidation rates, and mcrA explained ~10% in rewetted sites.
Overall, these findings suggest that drainage substantially suppresses methanogenic potential, while rewetting promotes partial functional recovery, particularly in bog systems and on timescales of at least decades. Integrating process-based and molecular data provides new insight into how land-use change shapes peatland methane cycling.
How to cite: Zivkovic, T., Deinert, S., Peltoniemi, K., Hultman, J., Korrensalo, A., Hájek, T., Urbanová, Z., Truu, J., Truu, M., Kull, A., and Liebner, S.: Land-use effects on microbial methane dynamics across European peatlands, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18049, https://doi.org/10.5194/egusphere-egu26-18049, 2026.
Peatlands, known to be important carbon sinks, have been transformed into sources of carbon due to human activities, contributing around 1 GtCO2 equivalents annually to global emissions. Denmark's Green Deal aims to restore 100,000 hectares of peatlands by 2030 to mitigate these emissions, with studies indicating that rewetting drained peatlands could significantly reduce greenhouse gas emissions. Microbial communities play a central role in peatland carbon cycling, driving the production of CO2 and CH4 through decomposition. Moreover, microbial communities are sensitive to changes in moisture conditions, particularly during dry and rewetting cycles. Previous studies show that CO2 rose during drought but returned to control levels during rewetting, while CH4 fluxes fell and remained suppressed throughout the rewetting period. Moreover, it has been found that microbial communities differed to a lesser extent between drained and rewetted peatland, than in drained and undrained peatlands, highlighting the importance of restoration.
Our aim in this study was to evaluate peatland restoration effectiveness in carbon sequestration and to improve the understanding of microbial controls on carbon dynamics in these ecosystems. To achieve this, we monitored CO2 and CH4 fluxes in restored and unrestored peatlands during spring and summer 2025, alongside assessments of microbial activity and community composition.
Preliminary results indicate that raising the water table in degraded peatlands reduces both CO2 and CH4 emissions, suggesting improved carbon storage following restoration. Despite decades of drainage, both sites retained high organic carbon stocks. Bacterial community composition differed more strongly between restored and unrestored sites than between seasons, and topsoil communities showed greater divergence from mid- and subsoil layers. Microbial activity analyses revealed that anoxic conditions limited bacterial growth, whereas fresh litter inputs and elevated temperatures stimulated it.
These findings deepen our understanding of how restoration influences peatland carbon processes and microbial ecology. By identifying conditions that promote carbon storage, this research supports the development of management strategies that enhance peatlands’ capacity to function as effective carbon sinks, contributing to climate change mitigation.
How to cite: Cruz Paredes, C., Olvasstovu Midjord, K., Aguilar Vilar, C., and Herzog, S.: Impact of peatland restoration on CO2 and CH4 emissions and microbial communities , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9827, https://doi.org/10.5194/egusphere-egu26-9827, 2026.
Peat soils store a disproportionate share of terrestrial carbon, yet agricultural drainage accelerates peat oxidation, converting long-term carbon sinks into substantial sources of greenhouse gases (GHGs). We conducted a two-year mesocosm experiment to quantify how water table level (WTL) and organic amendment type interactively regulate peat oxidation and emissions of CO2, CH4, and N2O under agricultural management. Three hydrological regimes were applied over 730 days: permanently saturated conditions (WTL 0 cm) during the first year, moderate drainage (WTL 20 cm) during the second year, and a continuously deeply drained business-as-usual control (WTL 40 cm). Each regime was combined with five amendments such as Miscanthus biochar, Miscanthus chips, paper waste, biosolids, and cereal straw and an unamended control.
Moderate drainage (WTL 20 cm) emerged as a critical threshold that constrained peat oxidation while strongly suppressing methanogenesis. Although CO2 emissions increased relative to saturated conditions, CH₄ fluxes declined by more than 90% compared with WTL 0 cm, where CH4 dominated total GHG output. This shift resulted in a 27-35% reduction in net CO2 -equivalent emissions, demonstrating a clear climate benefit of maintaining a moderately lowered water table. Labile, low C:N amendments (biosolids and straw) intensified CO2 and N2O emissions under WTL 20 cm, reflecting rapid microbial activation following oxygen exposure and enhanced peat decomposition. In contrast, Miscanthus biochar consistently reduced GHG emissions across hydrological conditions, lowering cumulative CO2-equivalent emissions by up to 52% relative to the deeply drained control after 730 days. chemical recalcitrance of biochar, high microporosity, and redox-buffering capacity promoted CH4 oxidation, limited N2O production, and stabilized native peat carbon against oxidative loss.
Our findings demonstrate that peat oxidation and associated GHG emissions can be substantially mitigated through the combined application of moderate water table regulation and stable, recalcitrant organic amendments. Integrating WTL management at -20 cm with biochar addition represents a robust, climate smart strategy for reducing emissions from agricultural peatlands while preserving long-term soil carbon stocks.
How to cite: Peduruhewa, J. H., Rhymes, J. M., Evans, C., Chadwick, D., and Jones, D.: Water table regulation and biochar amendments govern peat oxidation and greenhouse gas emissions in agricultural peatlands, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5981, https://doi.org/10.5194/egusphere-egu26-5981, 2026.
Globally, peatlands store one third of global soil carbon. Peatlands accumulate carbon under waterlogged anoxic conditions, but drainage increases oxygen availability causing peatland degradation. Therefore, drainage is responsible for ~2% of anthropogenic greenhouse gas (GHG) emissions. GHG emission estimates from drained peatlands are often based on hydrological proxies. In this research, we propose to improve these estimates by adding the redox potential that controls peat degradation more directly compared to hydrological proxies. We quantified in-situ soil production rates of CO2 and CH4 by combining in-situ redox potential measurements with corresponding laboratory basal respiration rates scaled to in-situ soil temperature. Using this approach, we estimated soil CO2 and CH4 production rates for 12 field sites over multiple years and validated these estimates by comparing them to aboveground Net Ecosystem Carbon Balance (NECB) measurements. We show that (1) laboratory incubation measurements can serve as a strong basis to estimate field-scale CO2 and CH4 emissions, (2) compared to water table depth, the redox potential is a more reliable parameter for estimating soil CO2 production, and (3) anaerobic respiration processes contribute substantially to peat decomposition and soil CO2 production. Our results provide valuable new insights for assessing GHG emissions from drained peatlands and enhances our understanding of aerobic and anaerobic peat decomposition processes.
How to cite: van der Velde, Y., Boonman, J., Tolunay, D., Keuskamp, J., Heffernan, L., Buzacott, A., Harpenslager, S. F., van Dijk, G., and Hefting, M.: Anaerobic decomposition contributions to greenhouse gas emissions of agriculturally used peatlands. , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14965, https://doi.org/10.5194/egusphere-egu26-14965, 2026.
Agricultural use of peat soils results in large amounts of GHG emissions. Drainage of peat soils leads to mineralisation and thus CO2 emissions. Wet conditions and copious amounts of carbon in fertilised peat soils generally also lead to high N2O emissions. Water infiltration systems (WIS) could regulate the groundwater table (GWT), allowing agricultural use of these soils while at the same time reducing peat oxidation, CO2-emissions and land subsidence. These changes to the groundwater will also affect N cycling processes yet it remains unclear how N2O emissions will be affected. We hypothesised that 1) active drainage reduces N2O emissions due to increased GWT stability, 2) a high GWT reduced N2O emissions due to limited mineralisation and 3) active drainage prevents large peaks in N2O emissions otherwise expected from fertilisers with a high mineral N content.
In this study, we conducted two one-year field studies. In the first study (2024), we tested how N2O emissions from peat soils were affected by grazing (urine and dung patches) and groundwater management (GWT and WIS). Treatments consisted of urine, dung patches and compaction or combinations thereof. These were laid out in a full factorial block design on 4 field parcels. In the second study (2025) we tested how different fertilisers affect N2O emissions from peat soils under two GWTs. Treatments consisted of an unfertilised control, standard synthetic fertilisers (CAN and Urea), Urea + urease- or nitrification inhibitor, cattle slurry and manure derived bio-based fertilisers (liquid and solid fraction of cattle slurry and ammonium sulphate). In both studies N2O emissions were measured using a closed chamber technique and gas monitor. In addition, grass yield and nitrogen uptake were recorded.
In 2024, N2O emissions were highest from all treatments containing urine patches. N2O emissions were highest from the field with a GWT. This could be explained by higher nitrogen mineralisation of peat, resulting in a high carbon availability for denitrification and thus increased N2O fluxes. Surprisingly we did not see an effect of WIS on N2O emissions. In 2025 GWT did not affect N2O emissions, yet crop N uptake was higher from the field with a low GWT. Emissions from ammonium sulphate (1% of applied N) were highest compared to the other fertilisers. Surprisingly all other treatments resulted in similarly low N2O emissions (<0.5%) with no effect of nitrification or urease inhibitor. Perhaps conditions such as temperature and precipitation inhibited emissions in 2025.
How to cite: Porre, R., Ros, M., Blondeau, E., and Velthof, G.: N2O emissions from fertilised peat soils under different water infiltration systems and groundwater levels, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-20061, https://doi.org/10.5194/egusphere-egu26-20061, 2026.
Advanced process-oriented models can reliably predict emissions of carbon containing greenhouse gases (CO₂ and CH₄) from both peatlands and arable soils. However, changes in land use, such as the conversion of peatlands into arable land or grassland following drainage, or the rewetting of drained peatlands, make it challenging for a single model to simulate soil processes and greenhouse gas emissions accurately across such different conditions.
We evaluated the LandscapeDNDC (LDNDC) model (Kraus et al., 2015) by comparing its simulations with field measurements of soil properties and CO2 and CH4 exchange rates (Eickenscheidt et al., 2015; Hommeltenberg et al., 2015). The default distribution of soil organic carbon (SOC) into pools with different decomposability, which is typically initialized in models based on the C:N ratio of soil organic matter (SOM), was ineffective for soils with a high organic matter content (>10% organic C). To address this, we distributed SOC into particulate and mineral-associated fractions (POM and MAOM) based on the concept of Lavallee et al (2020). Furthermore, we divided the MAOM into fast- and slow-decomposable pools, according to the C:N ratio of total organic matter (OM). The initial fraction of POM in total OM was derived from the total C content using the function proposed by Rühlmann (2020). Incorporating these changes into LDNDC’s soil biochemistry module improved agreement with observations and resolved the problem of underestimating ecosystem respiration in drained peatlands used for grassland or crop production. The improved initialization of SOC pools in the LDNDC model should enable more precise simulation of soil C stocks and GHG emissions at regional level, where soils with a wide range of SOC content need to be considered simultaneously.
References
Eickenscheidt, T., Heinichen, J., Drösler, M., 2015. The greenhouse gas balance of a drained fen peatland is mainly controlled by land-use rather than soil organic carbon content. Biogeosciences 12, 5161–5184. https://doi.org/10.5194/bg-12-5161-2015
Hommeltenberg, J., Mauder, M., Drösler, M., Heidbach, K., Werle, P., Schmid, H.P., 2014. Ecosystem scale methane fluxes in a natural temperate bog-pine forest in southern Germany. Agricultural and Forest Meteorology 198–199, 273–284. https://doi.org/10.1016/j.agrformet.2014.08.017
Kraus, D., Weller, S., Klatt, S., Haas, E., Wassmann, R., Kiese, R., Butterbach-Bahl, K., 2015. A new LandscapeDNDC biogeochemical module to predict CH4 and N2O emissions from lowland rice and upland cropping systems. Plant Soil 386, 125–149. https://doi.org/10.1007/s11104-014-2255-x
Lavallee, J.M., Soong, J.L., Cotrufo, M.F., 2020. Conceptualizing soil organic matter into particulate and mineral-associated forms to address global change in the 21st century. Global Change Biology 26, 261–273. https://doi.org/10.1111/gcb.14859
Ruehlmann, J., 2020. Soil particle density as affected by soil texture and soil organic matter: 1. Partitioning of SOM in conceptional fractions and derivation of a variable SOC to SOM conversion factor. Geoderma 375, 114542. https://doi.org/10.1016/j.geoderma.2020.114542
How to cite: Blagodatsky, S., Kraus, D., Braumann, F., Klatt, J., Drösler, M., Kiese, R., and Sheer, C.: Simulation of CO2 and CH4 emissions from peatlands and organic soils: an improvement of SOC pool initialization in LDNDC model, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11059, https://doi.org/10.5194/egusphere-egu26-11059, 2026.
Peat soil degradation in the Netherlands contributes an estimated 4.6–7 Mt CO₂ annually, accounting for approximately 3% of national greenhouse gas emissions. In response, the Dutch Climate Agreement (2019) established a target to reduce net CO₂ emissions from fen meadows by 1 Mt CO₂ per year by 2030. To achieve this objective, the Dutch National Research Programme on Greenhouse Gases in Peatlands (NOBV) implemented an intensive monitoring network that integrates chamber-based measurements with both on-site and airborne eddy covariance (EC) observations. A primary challenge in this context is attributing and upscaling CO₂ emissions across diverse peat types, soil conditions, groundwater regimes, and grassland management practices.
Direct measurement of peat oxidation at the ecosystem scale is not feasible; instead, it must be inferred from EC fluxes that encompass autotrophic respiration, heterotrophic decomposition, and management-induced vegetation turnover resulting from mowing and regrowth. Attribution remains challenging because conventional emission–response functions emphasise groundwater levels while neglecting soil physical properties and vegetation dynamics, which is a significant limitation in highly degraded, nutrient-rich peatlands.
Our modelling strategy consists of two components. First, we employ machine learning to analyse the data without imposing prior assumptions. Shapley-based attribution quantifies the contributions of groundwater depth, meteorological forcing, vegetation state, and mowing timing to fluxes, along with their interactions. These models identify nonlinear thresholds and regime-dependent behaviours that are challenging to specify a priori. We compare response structures across sites to assess sensitivities, rather than prescribing specific management scenarios.
Second, we develop a physics-based deep learning framework that integrates biophysically meaningful equations with adaptable learning components. Groundwater dynamics regulate oxygen availability and determine the proportion of organic matter exposed to air. Soil moisture profiles are used to characterise oxic and anoxic zones. Bulk density and porosity, which define degraded peat, constrain oxygen diffusion and moisture retention. By explicitly representing vegetation growth and mowing disturbances, we distinguish autotrophic respiration from peat oxidation.
Integrating soil physics and groundwater dynamics within a deep learning framework enhances both temporal robustness and cross-site transferability while maintaining model flexibility. This approach enables inference of peat oxidation from EC observations in a mechanistically consistent manner, thereby providing a robust foundation for evaluating mitigation strategies in intensively managed peatlands.
How to cite: Bataille, L., Kruijt, B., van der Poel, L., Franssen, W., Jans, W., van Huissteden, C., Zhao, H., Berghuis, H., Biermann, J., Andueza Kovacevic, I., Engel, F., Zerrudo, J., Ingle, R., Lippman, T. J., Cabezas-Dueñas, I., Nouta, R., Boon, V., Buzacott, A., van der Velde, Y., and Hutjes, R.: Deciphering eddy-covariance CO₂ flux patterns in Dutch peatlands, from machine-learning to physics-based deep-learning, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-2034, https://doi.org/10.5194/egusphere-egu26-2034, 2026.
Posters on site: Wed, 6 May, 14:00–15:45 | Hall X1
Organic soils can contribute significantly to greenhouse gas (GHG) emissions, particularly when drained. In the Netherlands, large areas of peat soils have been drained for agricultural use, resulting in peat oxidation, increased CO₂ emissions, and land subsidence. Microorganisms are the driving force behind peat degradation at a landscape scale, yet their activity is determined by the conditions at the pore scale. Understanding peat decomposition dynamics across landscapes therefore requires mechanistic understanding of microscale controls that link microbial processes to larger-scale subsidence and GHG emission patterns.
One factor shaping microscale conditions is the peat pore space and its architectural properties, including pore size distribution and connectivity. In the field, these properties are dynamic and respond to drainage and rewetting, as well as to microbial decomposition. Microorganisms are therefore both constrained by pore space properties and actively modify them. In contrast to natural peatlands, drained Dutch peatlands commonly exhibit a compacted, well-decomposed top layer with low pore volume that transitions into more porous and less decomposed peat with depth.
In this study, we aim to investigate how the volume and architecture of the peat pore space affect microbial metabolism and the resulting peat organic matter decomposition and GHG production. Using intact peat samples, we will establish field-relevant pore space volumes and architectures, as well as the microbial communities that inhabit them. In addition, we test a controlled laboratory setup in which homogenised peat is repacked to generate contrasting levels of pore space volume, while pore architecture is manipulated to create different pore size distributions. This design allows us to disentangle the effects of pore space volume from those of pore architecture. Pore structures will be resolved using X-ray microtomography, complemented by microbial community analysis and measurements of basal respiration.
We expect that variation in total pore volume, pore size distribution, and pore connectivity will alter microscale chemical and biological conditions, thereby impacting microbial metabolism, peat organic matter decomposition, and GHG emissions. By linking peat physical structure to microbial processes, this work seeks to provide mechanistic insights into peat decomposition, CO₂ emissions, and land subsidence.
How to cite: Rits, L., Erkens, G., Hefting, M. M., Keuskamp, J. A., and Kowalchuk, G. A.: Pore structure controls on microbial decomposition of peat organic matter and GHG production, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-21201, https://doi.org/10.5194/egusphere-egu26-21201, 2026.
Deep peat is typically more decomposed than shallow peat, and tends to be less available for microbial respiration, producing less methane and carbon dioxide per gram of stored carbon. Understanding why deep peat exhibits slower rates of decomposition – and especially the interplay of redox conditions and organic matter composition – is important for understanding the effects of peat drying and exposure of deep peat at the surface.
To investigate whether the metabolic capabilities of the deep peat microbiome or the reactivity of the peat itself limited breakdown of deep peat organic matter, we conducted a controlled incubation experiment. Incubations were set up to compare deep (>1m deep) and shallow peat (<30cm) from two temperate peatlands (an ombrotrophic, Sphagnum-dominated bog and a minerotrophic, graminoid-dominated fen). Peat samples were incubated under oxic and anoxic conditions, and a subset of vials were inoculated with a shallow microbial community extract, a shallow dissolved organic carbon (DOC) extract or a deep DOC extract from the corresponding site. Headspace gas concentrations (CO2 and CH4) were determined over the incubation period, while water samples were taken over the same period to observe changes in DOC concentrations and composition. Microbial community samples were collected at the beginning and end of the incubation period, and 16S rRNA gene sequencing was used to determine shifts in community composition.
We observed that exposure to oxygen and addition of the shallow microbial community increased microbial respiration in comparison to the anoxic deep peat controls. This suggests that the deep peat microbiome is metabolically capable of breaking down deep organic matter, but less efficient, and that without oxygen, the deep peat is less thermodynamically available. However, the amended deep peats do not exhibit CO2 production rates as high as those in the shallow peat control, indicating that organic matter recalcitrance still governs degradation rates even under aerobic conditions, with implications for the fate of deep peat carbon stocks exposed to oxygen.
How to cite: Sneddon-Jenkins, N., Vreeken, M., Oakeshott, A., Cheung, S., Ring-Hrubesh, F., Gallego-Sala, A., Pancost, R., and Bryce, C.: Constraints on Deep Peat Decomposition: Roles of Redox Conditions, Microbial Communities, and Organic Matter Reactivity, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17664, https://doi.org/10.5194/egusphere-egu26-17664, 2026.
Degradation of the UK’s peatlands has turned these landscapes from long-term carbon sinks to net sources, with lowland peatlands contributing a majority of these emissions. Rewetting is the primary means of restoring these peatlands, with the aim of limiting microbial aerobic decomposition of organic matter by raising the water table and reestablishing anoxic conditions. However, rewetting of former agricultural peat may also disrupt the cycling of redox-sensitive compounds, mobilise organic and mineral-bound nutrients, and modify the source of water supplying the peatland. How microbial communities respond to these hydrological and geochemical alterations remains unclear, even though they represent the primary control on peatland carbon balance and ecosystem function.
We have established a multi-year study at a former dairy farm on lowland peat soils in the Somerset Levels. We are conducting paired comparisons of drained and rewetted peat profiles within the same context that have resulted from blocking drainage ditches with sheet pile dams. Ditch blocking has been conducted at the site to facilitate rewetting but is also expected to alter the availability of nutrients within the peatland. We are investigating the primary geochemical controls on the microbiome, combining seasonal geochemical characterisation (water-extractable NO3-, NO2-, NH4+, PO43-, Fe2+, Fe3+), 16S rRNA gene sequencing; and bulk peat organic matter characterisation. Our findings highlight some of the challenges in restoring agricultural peatlands with both legacy and catchment-derived nutrient inputs. We find that macronutrient availability (in particular, water-extractable NH4+ and PO43-) remains elevated under the rewetting scenario, suggesting a potential legacy influence of prior land use on nutrient cycling. Moreover, across much of the peat profile, the major microbial constituents are shared between the drained and rewetted sites despite intervention. We identify taxa which may serve as markers of the redox interface, such as microaerophilic iron-oxidising bacteria, and explore the utility of such microbial indicators as a potential approach for predicting peatland function. The project demonstrates how microbial community sequencing can shed light on in-situ elemental cycling to inform ongoing management practices.
How to cite: Ring-Hrubesh, F., Alarcon-Prado, P., Powell, B., Randle, L., May, E., Zhang, Y., Vreeken, M., Pancost, R., and Bryce, C.: Tracking microbial responses to rewetting and nutrient mobilisation during agricultural peatland restoration, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-19491, https://doi.org/10.5194/egusphere-egu26-19491, 2026.
Freshwater lakes, despite covering only ~ 3% of Earth’s surface, are among the largest natural sources of methane to the atmosphere. Current global estimates of lake methane emissions, however, remain uncertain and likely underestimated due to the scarcity of long-term and high resolution datasets and the spatial and temporal complexity of freshwater lakes. Methane fluxes from lakes are influenced by many factors such as lake depth, organic matter input, seasonal biogeochemical dynamics and vegetation composition, making upscaling from individual systems challenging. In this study, we investigate the temporal dynamics of methane emissions from a shallow peat lake in the Netherlands. The lake is characterized by rich submerged vegetation dominated by two species: Potamogeton perfoliatus and Nitellopsis obtusa. Continuous eddy covariance (EC) measurements of methane fluxes, collected since December 2021, were combined with various water quality data to assess seasonal and interannual variabilities. Our results show a clear seasonal pattern, with substantially higher methane emissions during summer months (average of 165 mg m-2 d-1), compared to autumn, winter and spring (average of 50, 15 and 68 mg m-2 d-1, respectively). Through strong positive correlations, both water and air temperature were identified as the main drives of methane emissions, with the redox potential at the lake water-sediments interface also showing strong negative correlation. Interestingly, two distinct emission peaks were observed each early summer and again in late summer to early autumn. These peaks are likely linked to the macrophyte life cycle, with an early-season peak preceding full plant development, a mid-summer decrease possibly associated with oxygen input from the vegetation, and a late-season increase due to plant decomposition. These findings highlight the role of aquatic vegetation in methane release from shallow peat lakes. Better quantifying these temporal drivers is important to improve regional and global methane budgets.
How to cite: Zygadlowska, O. M., Boon, V. E. N., Marinissen, J., Kosten, S., and van der Velde, Y.: Methane emission dynamics of a shallow dutch peat lake: Insights from long-term eddy covariance monitoring, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14097, https://doi.org/10.5194/egusphere-egu26-14097, 2026.
Peatlands are significant terrestrial ecosystems that play a large role in regulating many global processes, resulting in a high social, environmental, and cultural importance. Despite this global distribution, these systems are far from uniform with differences in their hydrology, geochemistry, vegetation, and microbial communities, all shaping carbon processing pathways. This study investigates how contrasting peatland types across tropical and temperate zones differ in their biogeochemical characteristics, and to identify the dominant environmental and microbial drivers underpinning this variation. We examined microbial community composition, nutrient profiles, dissolved porewater gases, and detailed organic matter (OM) characterisation of eight peatlands from Colombia (n=4), Uganda (n=1), and the United Kingdom (n=3) to determine the influence on carbon cycling. First, we find that peat, which serves as microbial substrate, becomes enriched in aromatic and alkyl macromolecules with depth, which correlates with an increase abundance of Bathyarchaea and Spirochaeta, whilst a decrease in Methanobacterium and Burkholderia. This is consistent with a shift towards more processed OM and decreased substrate availability. Results also indicate a pH control, in relation to peatland type, on the abundance of Acidobacteriota. Sites with lower pHs (~ 4) are observed to have more Acidobacteriota in comparison to higher sites (~ 6) where Chloroflexi dominate more. Together, these results suggest that local geochemistry exerts a stronger influence on microbial community structure than latitude, further influencing OM decomposition pathways and carbon preservation. Overall, our data indicates that peat carbon stability is governed primarily by site-specific geochemistry rather than regional climate alone, highlighting the need for process-based constraints in predicting peatland carbon emissions under future environmental changes.
How to cite: Oakeshott, A., Vreeken, M., Jenkins, M., Zhang, Y., Cheung, S., Benavides Duque, J. C., Alarcon Prado, P., Kansiime, F., Kayendeke, E., Kagaba, C., Gallego-Sala, A., Pancost, R., and Bryce, C.: Environmental Controls on Carbon Stability in Peatlands: Integrating Microbial, Geochemical, and Organic Matter Variation, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18795, https://doi.org/10.5194/egusphere-egu26-18795, 2026.
Peatlands form due to the slow rate of organic matter decomposition characteristic of waterlogged and anaerobic conditions. The resulting organic matter accumulation acts as a long-term store of organic carbon. However, historical use of peatlands, such as peat extraction and drainage, has been detrimental to the carbon storing capabilities of these environments. With the UK’s set aims to achieve a net zero greenhouse gas emissions by 2050 there is an increased interest in the restoration and management of peatlands to help achieve these goals. Biochar has previously been applied to the surface of a peatland, encapsulating carbon for long periods of time due to its refractory nature. This method proved an effective carbon store whilst having no recorded significant or detrimental impact on the peatland itself. However, biochar production is expensive, and therefore, there is a desire to find a cheaper alternative.
This study has assessed the application of lignocellulosic material, specifically Calluna Vulgaris (heather) brash, to a peatland as an alternative to biochar addition. This study was performed on Hatfield Moors in South Yorkshire, UK. Employing a triplicate random block design with doses of 1 cm and 2 cm depth heather brash application alongside controls with no heather brash application. The plots were visited on a monthly basis for two years and monitored for:
- Peatland surface water quality monitoring – water table height, pH, ionic conductivity, UV absorbance at 400 nm, and organic carbon concentration;
- Peatland surface water nutrient concentration (nitrate and phosphate concentration);
- Peatland surface water terminal electron acceptor concentration (iron and sulphate concentration);
- Gas exchange of peatland (net ecosystem respiration, gross primary productivity, net ecosystem exchange) ; and
- Degradation of Calluna Vulgaris over the course of the study.
The study shows that heather brash could be a viable alternative to biochar as a means of augmenting carbon storage within peatlands.
How to cite: Reilly, P., Fearns_Nicol, E., Worrall, F., Knapp, J., and Small, J.: Is the application of lignocellulosic material an effective carbon storage improvement technique to peatlands?, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9417, https://doi.org/10.5194/egusphere-egu26-9417, 2026.
A relationship between the net ecosystem carbon balance (NECB) and the depth to water table (WTD) has been commonly quoted and used to justify restoration (Evans et al. (2021). However, there are some curious aspects to this relationship. Firstly, the relationship is linear over all depths which implies that the link between the carbon losses and water table is constant, i.e. if the water table in a peat declines then the impact is the same at 10 cm depth as it is at 75 cm depth. A constant susceptibility to degradation with depth in the peat profile would not fit with our understanding of peat accumulation. Secondly, the relationship has no significant fit for peatlands which are reported as net sinks – it only works for net sources. Tiemeyer et al. (2021) provided an alternative relationship based upon a Gompertz function where a linear relationship becomes a constant value at the extremes of water table depth. So in this study we expanded the available dataset and used Bayesian hierarchical modelling with the available factorial and covariate information to re-assess the link between NECB and depth to the water table. Within the hierarchical modelling both linearizable and non-linearizable relationships were considered. The data were considered by global peatland type (boreal, temperate and tropical) and the temperate peatlands were also considered separately by sub-type (cropland, drained, grassland, natural and rewetted). There were 752 studies that we could consider – 447 studies of temperate peatlands.
Our study shows that:
- NECB of boreal and temperate peatlands were not significantly different from each other, or from zero, but tropical peatlands were significant sources.
- NECB of natural, rewetted and drained sub-types were not significantly different from each other, but cropland and grassland sub-types were significantly different from all other sub-types.
- By global type there were significant relationships with depth to water table for temperate and tropical peatlands but not for boreal peatlands, and the slopes were not significantly different between tropical and temperate.
- There is little evidence that a linear relationship between NECB with WTD exists: previous published versions of the relationship were dominated by results from grasslands which are generally drier and larger sources than other settings, but within grasslands there is no relationship.
- Where a relationship does exist, then a Gompertz function solves some of the interpretation problems of a linear relationship. Although the Gompertz function itself has a linear portion.
- All relationships fitted poorly for sinks.
The study shows that Simpsons paradox may govern the apparent relationship between NECB and water table and that once a suitable grouping factor is applied any relationship breaks down: the use of non-linear relationships does not resolve the problem.
This finding has important implications for the management of peatlands and shows that a relationship between NECB and WTD is not common – what does that mean for our understanding of peatland accumulation and degradation? Further, if not WTD as a control then what are the common drivers on NECB?
Evans et al. (2021). Nature, 593(7860), 548–552.
Tiemeyer et al. (2021). . Global Change Biology, 22(12), 4134–4149.
How to cite: Worrall, F., Lopez Saldana, G., Bechtold, M., Page, S., Salvi, S., Tansey, K., Al-Sarrouh, Y., and Jory, I.: Re-visiting the relationship between net ecosystem carbon balance (NECB) and the depth to the water table – a case of Simpson paradox?, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9234, https://doi.org/10.5194/egusphere-egu26-9234, 2026.
The existence of peatlands relies on the balance of primary productivity and oxidation of organic matter. Oxidation requires a terminal electron acceptor (TEA). The most energetically favourable TEA is O2 followed, in order of reducing energy return, by NO3, Mn, Fe, and SO4. Organic matter itself can become a TEA with the production of methane (CH4). Organic matter will degrade faster the better access to the more energetically favourable TEAs. Therefore, the fate of the organic matter turnover in peatlands is related to the supply of TEAs. Typically, water tables are raised to limit the access of TEAs into the peat porewater, however, it is not only high water tables that are required but also stagnant water tables otherwise fresh TEAs are brought into the porewater.
This study looked at the hydrological and biogeochemical controls on organic matter turnover along a peat-covered hillslope using bunds. Bunds are used in peatlands to manipulate the water table to create environments for peat-forming species such as sphagnum mosses. To our knowledge, this is the only study with continuous pre-fire baseline data prior to a wildfire in a peatland system. Nine bunded plots and nine control plots were monitored monthly over a two year period, with sampling conducted upslope, within, and downslope of each bund. Measurements included water table depth, soil water chemistry (pH, conductivity, DOC, absorbance, cations and anions), and ecosystem CO₂ fluxes.
Pre-fire results showed significant differences absorbance down the hillslope, but no significant differences attributable to bund presence. Concentrations of DOC, iron and sulphate, conductivity, and water table depth did not differ significantly between bunded and control plots. Ecosystem respiration showed no significant variation related to bunds or hillslope position.
Following a wildfire, water table depths did not differ significantly from pre-fire conditions across the hillslope or between bunded and control plots. Similarly, concentrations of TEAs, including iron and sulphate, showed no statistically significant post-fire change. DOC concentrations, absorbance, conductivity, and CO₂ fluxes also remained within the range of pre-fire data.
Neither bund installation nor wildfire caused detectable changes in water table behaviour or TEA availability at this site over the two year study.
How to cite: Fearns-Nicol, E., Hirst, C., Worrall, F., and Knapp, J.: When peat burns: Wildfire and the fate of terminal electron acceptors. , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-20652, https://doi.org/10.5194/egusphere-egu26-20652, 2026.
