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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. Stronger increase of methane emissions from coastal wetlands by non‐native Spartina alterniflora than non‐native Phragmites australis

   https://doi.org/10.1002/ppp3.10578  

   Fuchs, Andrea; Davidson, Ian C; Megonigal, J Patrick; Devaney, John L; Simkanin, Christina; Noyce, Genevieve L; Lu, Meng; Cott, Grace M (January 2025, PLANTS, PEOPLE, PLANET)

   Societal Impact StatementThe invasive speciesS. alternifloraandP. australisare fast growing coastal wetland plants sequestering large amounts of carbon in the soil and protect coastlines against erosion and storm surges. In this global analysis, we found thatSpartinaandPhragmitesincrease methane but not nitrous oxide emissions, withPhragmiteshaving a lesser effect. The impact of the invasive species on emissions differed greatly among different types of native plant groups, providing valuable information to managers and policymakers during coastal wetland planning and restoration efforts. Further, our estimated net emissions per wetland plant group facilitate regional and national blue carbon estimates. SummaryGlobally,Spartina alternifloraandPhragmites australisare among the most pervasive invasive plants in coastal wetland ecosystems. Both species sequester large amounts of atmospheric carbon dioxide (CO₂) and biogenic carbon in soils but also support production and emission of methane (CH₄). In this study, we investigated the magnitude of their net greenhouse gas (GHG) release from invaded and non‐invaded habitats.We conducted a meta‐analysis of GHG fluxes associated with these two species and related soil carbon content and plant biomass in invaded coastal wetlands.Our results show that both invasive species increase CH₄fluxes compared to uninvaded coastal wetlands, but they do not significantly affect CO₂and N₂O fluxes. The magnitude of emissions fromSpartinaandPhragmitesdiffers among native habitats. GHG fluxes, soil carbon and plant biomass ofSpartina‐invaded habitats were highest compared to uninvaded mudflats and succulent forb‐dominated wetlands, while being lower compared to uninvaded mangroves (except for CH₄).This meta‐analysis highlights the important role of individual plant traits as drivers of change by invasive species on plant‐mediated carbon cycles. 

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3. A Synthesis of Global Coastal Ocean Greenhouse Gas Fluxes

   https://doi.org/10.1029/2023GB007803  

   Resplandy, L.; Hogikyan, A.; Müller, J. D.; Najjar, R. G.; Bange, H. W.; Bianchi, D.; Weber, T.; Cai, W. ‐J.; Doney, S. C.; Fennel, K.; et al (January 2024, Global Biogeochemical Cycles)

   Abstract The coastal ocean contributes to regulating atmospheric greenhouse gas concentrations by taking up carbon dioxide (CO₂) and releasing nitrous oxide (N₂O) and methane (CH₄). In this second phase of the Regional Carbon Cycle Assessment and Processes (RECCAP2), we quantify global coastal ocean fluxes of CO₂, N₂O and CH₄using an ensemble of global gap‐filled observation‐based products and ocean biogeochemical models. The global coastal ocean is a net sink of CO₂in both observational products and models, but the magnitude of the median net global coastal uptake is ∼60% larger in models (−0.72 vs. −0.44 PgC year⁻¹, 1998–2018, coastal ocean extending to 300 km offshore or 1,000 m isobath with area of 77 million km²). We attribute most of this model‐product difference to the seasonality in sea surface CO₂partial pressure at mid‐ and high‐latitudes, where models simulate stronger winter CO₂uptake. The coastal ocean CO₂sink has increased in the past decades but the available time‐resolving observation‐based products and models show large discrepancies in the magnitude of this increase. The global coastal ocean is a major source of N₂O (+0.70 PgCO₂‐e year⁻¹in observational product and +0.54 PgCO₂‐e year⁻¹in model median) and CH₄(+0.21 PgCO₂‐e year⁻¹in observational product), which offsets a substantial proportion of the coastal CO₂uptake in the net radiative balance (30%–60% in CO₂‐equivalents), highlighting the importance of considering the three greenhouse gases when examining the influence of the coastal ocean on climate. 

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4. Lagged Wetland CH ₄ Flux Response in a Historically Wet Year

   https://doi.org/10.1029/2021JG006458  

   Turner, J.; Desai, A. R.; Thom, J.; Wickland, K. P. (November 2021, Journal of Geophysical Research: Biogeosciences)

   Abstract While a stimulating effect of plant primary productivity on soil carbon dioxide (CO₂) emissions has been well documented, links between gross primary productivity (GPP) and wetland methane (CH₄) emissions are less well investigated. Determination of the influence of primary productivity on wetland CH₄emissions (FCH₄) is complicated by confounding influences of water table level and temperature on CH₄production, which also vary seasonally. Here, we evaluate the link between preceding GPP and subsequent FCH₄at two fens in Wisconsin using eddy covariance flux towers, Lost Creek (US‐Los) and Allequash Creek (US‐ALQ). Both wetlands are mosaics of forested and shrub wetlands, with US‐Los being larger in scale and having a more open canopy. Co‐located sites with multi‐year observations of flux, hydrology, and meteorology provide an opportunity to measure and compare lag effects on FCH₄without interference due to differing climate. Daily average FCH₄from US‐Los reached a maximum of 47.7 ηmol CH₄m⁻² s⁻¹during the study period, while US‐ALQ was more than double at 117.9 ηmol CH₄ m⁻² s⁻¹. The lagged influence of GPP on temperature‐normalized FCH₄(T_air‐FCH₄) was weaker and more delayed in a year with anomalously high precipitation than a following drier year at both sites. FCH₄at US‐ALQ was lower coincident with higher stream discharge in the wet year (2019), potentially due to soil gas flushing during high precipitation events and lower water temperatures. Better understanding of the lagged influence of GPP on FCH₄due to this study has implications for climate modeling and more accurate carbon budgeting. 

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5. Delayed herbivory by migratory geese increases summer‐long CO ₂ uptake in coastal western Alaska

   https://doi.org/10.1111/gcb.14473  

   Leffler, A. Joshua; Beard, Karen H.; Kelsey, Katharine C.; Choi, Ryan T.; Schmutz, Joel A.; Welker, Jeffrey M. (November 2018, Global Change Biology)

   Abstract The advancement of spring and the differential ability of organisms to respond to changes in plant phenology may lead to “phenological mismatches” as a result of climate change. One potential for considerable mismatch is between migratory birds and food availability in northern breeding ranges, and these mismatches may have consequences for ecosystem function. We conducted a three‐year experiment to examine the consequences for CO₂exchange of advanced spring green‐up and altered timing of grazing by migratory Pacific black brant in a coastal wetland in western Alaska. Experimental treatments represent the variation in green‐up and timing of peak grazing intensity that currently exists in the system. Delayed grazing resulted in greater net ecosystem exchange (NEE) and gross primary productivity (GPP), while early grazing reduced CO₂uptake with the potential of causing net ecosystem carbon (C) loss in late spring and early summer. Conversely, advancing the growing season only influenced ecosystem respiration (ER), resulting in a small increase in ER with no concomitant impact on GPP or NEE. The experimental treatment that represents the most likely future, with green‐up advancing more rapidly than arrival of migratory geese, results in NEE changing by 1.2 µmol m⁻² s⁻¹toward a greater CO₂sink in spring and summer. Increased sink strength, however, may be mitigated by early arrival of migratory geese, which would reduce CO₂uptake. Importantly, while the direct effect of climate warming on phenology of green‐up has a minimal influence on NEE, the indirect effect of climate warming manifest through changes in the timing of peak grazing can have a significant impact on C balance in northern coastal wetlands. Furthermore, processes influencing the timing of goose migration in the winter range can significantly influence ecosystem function in summer habitats. 

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