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1. Responding to rising waters and temperatures: greenhouse gas flux from a high-latitude coastal wetland

   https://doi.org/10.1088/1748-9326/adff98  

   Kelsey, Katharine C; Leffler, A Joshua; Petit_Bon, Matteo; Barr, Briana N; Beard, Karen H (September 2025, Environmental Research Letters)

   Abstract Climate change is exposing coastal landscapes to more flooding, in addition to rapidly rising temperatures. These changes are critical in the Arctic where the effects of sea level rise are exacerbated by the loss of sea ice protecting coasts, subsidence as permafrost thaws, and a projected increase in storms. Such changes will likely alter the land-atmosphere gas exchange of high-latitude coastal ecosystems, but the effects of flooding with warming remain unexplored. In this work we use a field experiment to examine the interacting effects of increased tidal flooding and warming on land-atmosphere CO₂and CH₄exchange in the coastal Yukon–Kuskokwim Delta, a large sub-Arctic wetland and tundra complex in western Alaska. We inundated dammed plots to simulate two levels of future flooding: low-intensity flooding represented by one day of flooding per summer-month (June, July and August), and high-intensity flooding represented by three-consecutive days of flooding per summer-month, crossed with a warming treatment of 1.4 °C. We found that both flooding and warming influenced greenhouse gas (GHG) exchange. Low-intensity flooding reduced net CO₂uptake by 20% (0.78µmol m⁻²s⁻¹) regardless of temperature, and marginally increased CH₄emissions 0.83 nmol m⁻²s⁻¹(33%) under ambient temperature, while decreasing CH₄emissions by −1.96 nmol m⁻²s⁻¹(40%) under warming. In contrast, high-intensity flooding restored net CO₂uptake to control levels due to enhanced primary productivity under both temperature treatments. High-intensity flooding decreased CH₄emissions under ambient temperature by 0.76 nmol m⁻²s⁻¹(30%), but greatly increased emissions under warming by 4.68 nmol m⁻²s⁻¹(265%), presumably driven by increased plant-mediated CH₄transport. These findings reveal that GHG exchange responds rapidly and non-linearly to intensifying flooding, and highlight the importance of short-term flooding dynamics and warming in shaping future carbon cycling in this Arctic coastal wetland. 

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2. Response of CO ₂ and CH ₄ emissions from Arctic tundra soils to a multifactorial manipulation of water table, temperature and thaw depth

   https://doi.org/10.1088/2752-664X/ad089d  

   Best, K; Zona, D; Briant, E; Lai, Chun-Ta; Lipson, D A; McEwing, K R; Davidson, S J; Oechel, W C (November 2023, Environmental Research: Ecology)

   Goetz, Scott (Ed.)

   Abstract Significant uncertainties persist concerning how Arctic soil tundra carbon emission responds to environmental changes. In this study, 24 cores were sampled from drier (high centre polygons and rims) and wetter (low centre polygons and troughs) permafrost tundra ecosystems. We examined how soil CO₂and CH₄fluxes responded to laboratory-based manipulations of soil temperature (and associated thaw depth) and water table depth, representing current and projected conditions in the Arctic. Similar soil CO₂respiration rates occurred in both the drier and the wetter sites, suggesting that a significant proportion of soil CO₂emission occurs via anaerobic respiration under water-saturated conditions in these Arctic tundra ecosystems. In the absence of vegetation, soil CO₂respiration rates decreased sharply within the first 7 weeks of the experiment, while CH₄emissions remained stable for the entire 26 weeks of the experiment. These patterns suggest that soil CO₂emission is more related to plant input than CH₄production and emission. The stable and substantial CH₄emission observed over the entire course of the experiment suggests that temperature limitations, rather than labile carbon limitations, play a predominant role in CH₄production in deeper soil layers. This is likely due to the presence of a substantial source of labile carbon in these carbon-rich soils. The small soil temperature difference (a median difference of 1 °C) and a more substantial thaw depth difference (a median difference of 6 cm) between the high and low temperature treatments resulted in a non-significant difference between soil CO₂and CH₄emissions. Although hydrology continued to be the primary factor influencing CH₄emissions, these emissions remained low in the drier ecosystem, even with a water table at the surface. This result suggests the potential absence of a methanogenic microbial community in high-centre polygon and rim ecosystems. Overall, our results suggest that the temperature increases reported for these Arctic regions are not responsible for increases in carbon losses. Instead, it is the changes in hydrology that exert significant control over soil CO₂and CH₄emissions. 

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3. Short-term elevated CO _₂ enhances primary productivity and CH _₄ emissions in wet sedge arctic soils

   https://doi.org/10.1088/2752-664X/ae3831  

   Sirivat, Danielle; Luedke, Sara; Paw_U, K T; Lipson, D A; Oechel, W C; Bernabe, Kristine; Zona, Donatella (February 2026, Environmental Research: Ecology)

   Abstract The Arctic tundra is a significant source of CH₄generated through anaerobic methanogenesis, and vegetation explains much of the heterogeneity in CH₄fluxes across the Arctic landscape. Wet sedge-dominated tundra exhibits particularly high rates of CH₄flux due to the presence of aerenchyma and therefore, plant-mediated transport of CH₄. However, the response of CH₄to future CO₂concentrations remains largely uncertain. Model predictions assumed that elevated CO₂(eCO₂) will increase primary production and, as a result, CH₄emissions, but this has been poorly tested given the challenges of conducting eCO₂experiments in the Arctic. To address this knowledge gap, we tested the response of CH₄fluxes in soil and vegetation cores from a wet-sedge tundra ecosystem in Alaska to eCO₂. The eCO₂stimulated plant productivity and increased CH₄emissions in a short-term treatment. The instantaneous response suggests a direct contribution of plant-derived labile carbon input in stimulating methanogenesis despite the large soil carbon store in these tundra ecosystems. 

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4. Resolving the Carbon‐Climate Feedback Potential of Wetland CO ₂ and CH ₄ Fluxes in Alaska

   https://doi.org/10.1029/2022GB007524  

   Ma, Shuang; Bloom, A Anthony; Watts, Jennifer D; Quetin, Gregory R; Donatella, Zona; Euskirchen, Eugénie S; Norton, Alexander J; Yin, Yi; Levine, Paul A; Braghiere, Renato K; et al (September 2023, Global Biogeochemical Cycles)

   Abstract Boreal‐Arctic regions are key stores of organic carbon (C) and play a major role in the greenhouse gas balance of high‐latitude ecosystems. The carbon‐climate (C‐climate) feedback potential of northern high‐latitude ecosystems remains poorly understood due to uncertainty in temperature and precipitation controls on carbon dioxide (CO₂) uptake and the decomposition of soil C into CO₂and methane (CH₄) fluxes. While CH₄fluxes account for a smaller component of the C balance, the climatic impact of CH₄outweighs CO₂(28–34 times larger global warming potential on a 100‐year scale), highlighting the need to jointly resolve the climatic sensitivities of both CO₂and CH₄. Here, we jointly constrain a terrestrial biosphere model with in situ CO₂and CH₄flux observations at seven eddy covariance sites using a data‐model integration approach to resolve the integrated environmental controls on land‐atmosphere CO₂and CH₄exchanges in Alaska. Based on the combined CO₂and CH₄flux responses to climate variables, we find that 1970‐present climate trends will induce positive C‐climate feedback at all tundra sites, and negative C‐climate feedback at the boreal and shrub fen sites. The positive C‐climate feedback at the tundra sites is predominantly driven by increased CH₄emissions while the negative C‐climate feedback at the boreal site is predominantly driven by increased CO₂uptake (80% from decreased heterotrophic respiration, and 20% from increased photosynthesis). Our study demonstrates the need for joint observational constraints on CO₂and CH₄biogeochemical processes—and their associated climatic sensitivities—for resolving the sign and magnitude of high‐latitude ecosystem C‐climate feedback in the coming decades. 

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5. Intensified Positive Arctic–Methane Feedback under IPCC Climate Scenarios in the 21st Century

   https://doi.org/10.34133/ehs.0185  

   Wang, Yihui; He, Liyuan; Liu, Jianzhao; Arndt, Kyle A; Mazza_Rodrigues, Jorge L; Zona, Donatella; Lipson, David A; Oechel, Walter C; Ricciuto, Daniel M; Wullschleger, Stan D; et al (April 2024, Ecosystem Health and Sustainability)

   The positive Arctic–methane (CH₄) feedback forms when more CH₄is released from the Arctic tundra to warm the climate, further stimulating the Arctic to emit CH₄. This study utilized the CLM-Microbe model to project CH₄emissions across five distinct Arctic tundra ecosystems on the Alaska North Slope, considering three Shared Socioeconomic Pathway (SSP) scenarios using climate data from three climate models from 2016 to 2100. Employing a hyper-resolution of 5 m × 5 m within 40,000 m²domains accounted for the Arctic tundra’s high spatial heterogeneity; three sites were near Utqiaġvik (US-Beo, US-Bes, and US-Brw), with one each in Atqasuk (US-Atq) and Ivotuk (US-Ivo). Simulated CH₄emissions substantially increased by a factor of 5.3 to 7.5 under the SSP5–8.5 scenario compared to the SSP1–2.6 and SSP2–4.5 scenarios. The projected CH₄emissions exhibited a stronger response to rising temperature under the SSP5–8.5 scenario than under the SSP1–2.6 and SSP2–4.5 scenarios, primarily due to strong temperature dependence and the enhanced precipitation-induced expansion of anoxic conditions that promoted methanogenesis. The CH₄transport via ebullition and plant-mediated transport is projected to increase under all three SSP scenarios, and ebullition dominated CH₄transport by 2100 across five sites. Projected CH₄emissions varied in temperature sensitivity, with a Q₁₀range of 2.7 to 60.9 under SSP1–2.6, 3.8 to 17.6 under SSP2–4.5, and 5.7 to 17.2 under SSP5–8.5. Compared with the other three sites, US-Atq and US-Ivo were estimated to have greater increases in CH₄emissions due to warmer temperatures and higher precipitation. The fact that warmer sites and warmer climate scenarios had higher CH₄emissions suggests an intensified positive Arctic–CH₄feedback in the 21st century. Microbial physiology and substrate availability dominated the enhanced CH₄production. The simulated intensified positive feedback underscores the urgent need for a more mechanistic understanding of CH₄dynamics and the development of strategies to mitigate CH₄across the Arctic. 

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