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1. Salinity and Moisture Influence CO ₂ and CH ₄ Emissions From High‐Latitude Coastal Soils

   https://doi.org/10.1029/2024JG008629  

   Barr, B N; Kelsey, K C; Leffler, A J; Petit_Bon, M; Beard, K H (July 2025, Journal of Geophysical Research: Biogeosciences)

   Abstract Sea level rise and more frequent and larger storms will increase saltwater flooding in coastal terrestrial ecosystems, altering soil‐atmosphere CO₂and CH₄exchange. Understanding these impacts is particularly relevant in high‐latitude coastal soils that hold large carbon stocks but where the interaction of salinity and moisture on greenhouse gas flux remains unexplored. Here, we quantified the effects of salinity and moisture on CO₂and CH₄fluxes from low‐Arctic coastal soils from three landscape positions (two Wetlands and Upland Tundra) distinguished by elevation, flooding frequency, soil characteristics, and vegetation. We used a full factorial laboratory incubation experiment of three soil moisture levels (40%, 70%, or 100% saturation) and four salinity levels (freshwater, 3, 6, or 12 ppt). Salinity and soil moisture were important controls on CO₂and CH₄emissions across all landscape positions. In saturated soil, CO₂emissions increased with salinity in the lower elevation landscape positions but not in the Upland Tundra soil. Saturated soil was necessary for large CH₄emissions. CH₄emissions were greatest with low salinity, or after 11 weeks of incubation when SO₄²⁻was exhausted allowing for methanogenesis as the dominant mechanism of anaerobic respiration. In partially saturated soil, greater salinity suppressed CO₂production in all soils. CH₄fluxes were overall quite low, but increased between 3 and 6 ppt in the Tundra. In the future, a small increase in floodwater salinity may increase CO₂production while suppressing CH₄production; however, where water is impounded, CH₄production could become large, particularly in the landscapes most likely to flood. 

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2. Nutrient Release From Permafrost Thaw Enhances CH ₄ Emissions From Arctic Tundra Wetlands

   https://doi.org/10.1029/2018JG004641  

   Lara, Mark J; Lin, David H; Andresen, Christian; Lougheed, Vanessa L; Tweedie, Craig E (June 2019, Journal of Geophysical Research: Biogeosciences)

   Abstract High‐latitude climate change has impacted vegetation productivity, composition, and distribution across tundra ecosystems. Over the past few decades in northern Alaska, emergent macrophytes have increased in cover and density, coincident with increased air and water temperature, active layer depth, and nutrient availability. Unraveling the covarying climate and environmental controls influencing long‐term change trajectories is paramount for advancing our predictive understanding of the causes and consequences of warming in permafrost ecosystems. Within a climate‐controlled carbon flux monitoring system, we evaluate the impact of elevated nutrient availability associated with degraded permafrost (high‐treatment) and maximum field observations (low‐treatment), on aquatic macrophyte growth and methane (CH₄) emissions. Nine aquaticArctophila fulva‐dominated tundra monoliths were extracted from tundra ponds near Utqiaġvik, Alaska, and placed in growth chambers that controlled ambient conditions (i.e., light, temperature, and water table), while measuring plant growth (periodically) and CH₄fluxes (continuously) for 12 weeks. Results indicate that high nutrient treatments similar to that released from permafrost thaw can increase macrophyte biomass and total CH₄emission by 54 and 64%, respectively. However, low treatments did not respond to fertilization. We estimate that permafrost thaw in tundra wetlands near Utqiaġvik have the potential to enhance regional CH₄efflux by 30%. This study demonstrates the sensitivity of arctic tundra wetland biogeochemistry to nutrient release from permafrost thaw and suggests the decadal‐scale expansion ofA. fulva‐dominant aquatic plant communities, and increased CH₄emissions in the region were likely in response to thawing permafrost, potentially representing a novel case study of the permafrost carbon feedback to warming. 

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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. Persistent net release of carbon dioxide and methane from an Alaskan lowland boreal peatland complex

   https://doi.org/10.1111/gcb.17139  

   Euskirchen, Eugénie S.; Edgar, Colin W.; Kane, Evan S.; Waldrop, Mark P.; Neumann, Rebecca B.; Manies, Kristen L.; Douglas, Thomas A.; Dieleman, Catherine; Jones, Miriam C.; Turetsky, Merritt R. (January 2024, Global Change Biology)

   Abstract Permafrost degradation in peatlands is altering vegetation and soil properties and impacting net carbon storage. We studied four adjacent sites in Alaska with varied permafrost regimes, including a black spruce forest on a peat plateau with permafrost, two collapse scar bogs of different ages formed following thermokarst, and a rich fen without permafrost. Measurements included year‐round eddy covariance estimates of net carbon dioxide (CO₂), mid‐April to October methane (CH₄) emissions, and environmental variables. From 2011 to 2022, annual rainfall was above the historical average, snow water equivalent increased, and snow‐season duration shortened due to later snow return. Seasonally thawed active layer depths also increased. During this period, all ecosystems acted as slight annual sources of CO₂(13–59 g C m⁻² year⁻¹) and stronger sources of CH₄(11–14 g CH₄ m⁻²from ~April to October). The interannual variability of net ecosystem exchange was high, approximately ±100 g C m⁻² year⁻¹, or twice what has been previously reported across other boreal sites. Net CO₂release was positively related to increased summer rainfall and winter snow water equivalent and later snow return. Controls over CH₄emissions were related to increased soil moisture and inundation status. The dominant emitter of carbon was the rich fen, which, in addition to being a source of CO₂, was also the largest CH₄emitter. These results suggest that the future carbon‐source strength of boreal lowlands in Interior Alaska may be determined by the area occupied by minerotrophic fens, which are expected to become more abundant as permafrost thaw increases hydrologic connectivity. Since our measurements occur within close proximity of each other (≤1 km²), this study also has implications for the spatial scale and data used in benchmarking carbon cycle models and emphasizes the necessity of long‐term measurements to identify carbon cycle process changes in a warming climate. 

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5. 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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