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Climate change induced drying and flooding may alter the redox conditions of organic matter decomposition in peat soils. The seasonal and intermittent changes in pore water solutes (NDue to image rights restrictions, multiple line equation(s) cannot be graphically displayed. , Fe2+, SODue to image rights restrictions, multiple line equation(s) cannot be graphically displayed. , H2S, acetate) and dissolved soil gases (CO2, O2, CH4, H2) under natural water table fluctuations were compared to the response under a reinforced drying and flooding in fen peats. Oxygen penetration during dryings led to CO2 and CH4 degassing and to a regeneration of dissolved electron acceptors (NODue to image rights restrictions, multiple line equation(s) cannot be graphically displayed., Fe3+ and SODue to image rights restrictions, multiple line equation(s) cannot be graphically displayed. ). Drying intensity controlled the extent of the electron acceptor regeneration. Iron was rapidly reduced and sulfate pools ∼1mmol L-1 depleted upon rewetting and CH4 did not substantially accumulate until sulfate levels declined to ∼100 µmol l-1. The post-rewetting recovery of soil methane concentrations to levels ∼80 µmol l-1 needed 40-50 days after natural drought. This recovery was prolonged after experimentally reinforced drought. A greater regeneration of electron acceptors during drying was not related to prolonged methanogenesis suppression after rewetting. Peat compaction, solid phase content of reactive iron and total reduced inorganic sulfur and organic matter content controlled oxygen penetration, the regeneration of electron acceptors and the recovery of CH4 production, respectively. Methane production was maintained despite moderate water table decline of 20 cm in denser peats. Flooding led to accumulation of acetate and H2, promoted CH4 production and strengthened the co-occurrence of iron and sulfate reduction and methanogenesis. Mass balances during drying and flooding indicated that an important fraction of the electron flow must have been used for the generation and consumption of electron acceptors in the solid phase or other mechanisms. In contrast to flooding, dry-wet cycles negatively affect methane production on a seasonal scale but this impact might strongly depend on drying intensity and on the peat matrix, whose structure and physical properties influence moisture content. [ABSTRACT FROM AUTHOR]

Permafrost thaw in northern peatlands causes collapse of permafrost peat plateaus and thermokarst bog development, with potential impacts on atmospheric greenhouse gas exchange. Here, we measured methane and carbon dioxide fluxes over 3 years (including winters) using static chambers along two permafrost thaw transects in northwestern Canada, spanning young (~30 years since thaw), intermediate and mature thermokarst bogs (~200 years since thaw). Young bogs were wetter, warmer and had more hydrophilic vegetation than mature bogs. Methane emissions increased with wetness and soil temperature (40 cm depth) and modelled annual estimates were greatest in the young bog during the warmest year and lowest in the mature bog during the coolest year (21 and 7 g C-CH 4  m -2  year -1 , respectively). The dominant control on net ecosystem exchange (NEE) in the mature bog (between +20 and -54 g C-CO 2 m -2  year -1 ) was soil temperature (5 cm), causing net CO 2 loss due to higher ecosystem respiration (ER) in warmer years. In contrast, wetness controlled NEE in the young and intermediate bogs (between +55 and -95 g C-CO 2 m -2  year -1 ), where years with periodic inundation at the beginning of the growing season caused greater reduction in gross primary productivity than in ER leading to CO 2 loss. Winter fluxes (November-April) represented 16% of annual ER and 38% of annual CH 4 emissions. Our study found NEE of thermokarst bogs to be close to neutral and rules out large CO 2 losses under current conditions. However, high CH 4 emissions after thaw caused a positive net radiative forcing effect. While wet conditions favouring high CH 4 emissions only persist for the initial young bog period, we showed that continued climate warming with increased ER, and thus, CO 2 losses from the mature bog can cause net positive radiative forcing which would last for centuries after permafrost thaw., (© 2024 The Author(s). Global Change Biology published by John Wiley & Sons Ltd.)

Vast stores of millennial-aged soil carbon (MSC) in permafrost peatlands risk leaching into the contemporary carbon cycle after thaw caused by climate warming or increased wildfire activity. Here we tracked the export and downstream fate of MSC from two peatland-dominated catchments in subarctic Canada, one of which was recently affected by wildfire. We tested whether thermokarst bog expansion and deepening of seasonally thawed soils due to wildfire increased the contributions of MSC to downstream waters. Despite being available for lateral transport, MSC accounted for ≤6% of dissolved organic carbon (DOC) pools at catchment outlets. Assimilation of MSC into the aquatic food web could not explain its absence at the outlets. Using δ 13 C-Δ 14 C-δ 15 N-δ 2 H measurements, we estimated only 7% of consumer biomass came from MSC by direct assimilation and algal recycling of heterotrophic respiration. Recent wildfire that caused seasonally thawed soils to reach twice as deep in one catchment did not change these results. In contrast to many other Arctic ecosystems undergoing climate warming, we suggest waterlogged peatlands will protect against downstream delivery and transformation of MSC after climate- and wildfire-induced permafrost thaw., (© 2021 The Authors. Global Change Biology published by John Wiley & Sons Ltd.)

Despite occupying a small fraction of the landscape, fluvial networks are disproportionately large emitters of CO 2 and CH 4 , with the potential to offset terrestrial carbon sinks. Yet the extent of this offset remains uncertain, because current estimates of fluvial emissions often do not integrate beyond individual river reaches and over the entire fluvial network in complex landscapes. Here we studied broad patterns of concentrations and isotopic signatures of CO 2 and CH 4 in 50 streams in the western boreal biome of Canada, across an area of 250,000 km 2 . Our study watersheds differ starkly in their geology (sedimentary and shield), permafrost extent (sporadic to extensive discontinuous) and land cover (large variability in lake and wetland extents). We also investigated the effect of wildfire, as half of our study streams drained watersheds affected by megafires that occurred 3 years prior. Similar to other boreal regions, we found that stream CO 2 concentrations were primarily associated with greater terrestrial productivity and warmer climates, and decreased downstream within the fluvial network. No effects of recent wildfire, bedrock geology or land cover composition were found. The isotopic signatures suggested dominance of biogenic CO 2 sources, despite dominant carbonate bedrock in parts of the study region. Fluvial CH 4 concentrations had a high variability which could not be explained by any landscape factors. Estimated fluvial CO 2 emissions were 0.63 (0.09-6.06, 95% CI) and 0.29 (0.17-0.44, 95% CI) g C m -2  year -1 at the landscape scale using a stream network modelling and a mass balance approach, respectively, a small but potentially important component of the landscape C balance. These fluvial CO 2 emissions are lower than in other northern regions, likely due to a drier climate. Overall, our study suggests that fluvial CO 2 emissions are unlikely to be sensitive to altered fire regimes, but that warming and permafrost thaw will increase emissions significantly., (© 2019 John Wiley & Sons Ltd.)

Carbon release from thawing permafrost soils could significantly exacerbate global warming as the active-layer deepens, exposing more carbon to decay. Plant community and soil properties provide a major control on this by influencing the maximum depth of thaw each summer (active-layer thickness; ALT), but a quantitative understanding of the relative importance of plant and soil characteristics, and their interactions in determine ALTs, is currently lacking. To address this, we undertook an extensive survey of multiple vegetation and edaphic characteristics and ALTs across multiple plots in four field sites within boreal forest in the discontinuous permafrost zone (NWT, Canada). Our sites included mature black spruce, burned black spruce and paper birch, allowing us to determine vegetation and edaphic drivers that emerge as the most important and broadly applicable across these key vegetation and disturbance gradients, as well as providing insight into site-specific differences. Across sites, the most important vegetation characteristics limiting thaw (shallower ALTs) were tree leaf area index (LAI), moss layer thickness and understory LAI in that order. Thicker soil organic layers also reduced ALTs, though were less influential than moss thickness. Surface moisture (0-6 cm) promoted increased ALTs, whereas deeper soil moisture (11-16 cm) acted to modify the impact of the vegetation, in particular increasing the importance of understory or tree canopy shading in reducing thaw. These direct and indirect effects of moisture indicate that future changes in precipitation and evapotranspiration may have large influences on ALTs. Our work also suggests that forest fires cause greater ALTs by simultaneously decreasing multiple ecosystem characteristics which otherwise protect permafrost. Given that vegetation and edaphic characteristics have such clear and large influences on ALTs, our data provide a key benchmark against which to evaluate process models used to predict future impacts of climate warming on permafrost degradation and subsequent feedback to climate., (© 2016 The Authors. Global Change Biology Published by John Wiley & Sons Ltd.)

The quantitative impact of intense drought and rewetting on gas exchange in ombrotrophic bogs is still uncertain. In particular, we lack studies investigating multitudes of sites with different soil properties and nitrogen (N) and sulfur (S) deposition under consistent environmental conditions. We explored the timing and magnitude of change in CO2 (Respiration, Gross Primary Production - GPP, and Net Exchange - NE) and CH4 fluxes during an initial wet, a prolonged dry (~100 days), and a subsequent wet period (~230 days) at 12 °C in 14 Sphagnum peat mesocosms collected in hollows from bogs in the UK, Ireland, Poland, and Slovakia. The relationship of N and S deposition with GPP, respiration, and CH4 exchange was investigated. Nitrogen deposition increased CO2 fluxes and GPP more than respiration, at least up to about 15 kg N ha(-1)  yr(-1) . All mesocosms became CO2 sources during drying and most of them when the entire annual period was considered. Response of GPP to drying was faster than that of respiration and contributed more to the change in NE; the effect was persistent and few sites recovered "predry" GPP by the end of the wet phase. Respiration was higher during the dry phase, but did not keep increasing as WT kept falling and peaked within the initial 33 days of drying; the change was larger when differences in humification with depth were small. CH4 fluxes strongly peaked during early drought and water table decline. After rewetting, methanogenesis recovered faster in dense peats, but CH4 fluxes remained low for several months, especially in peats with higher inorganic reduced sulfur content, where sulfate was generated and methanogenesis remained suppressed. Based on a range of European sites, the results support the idea that N and S deposition and intense drought can substantially affect greenhouse gas exchange on the annual scale., (© 2016 John Wiley & Sons Ltd.)