Dataset Information

Methane emissions offset atmospheric carbon dioxide uptake in coastal macroalgae, mixed vegetation and sediment ecosystems.

ABSTRACT: Coastal ecosystems can efficiently remove carbon dioxide (CO₂) from the atmosphere and are thus promoted for nature-based climate change mitigation. Natural methane (CH₄) emissions from these ecosystems may counterbalance atmospheric CO₂ uptake. Still, knowledge of mechanisms sustaining such CH₄ emissions and their contribution to net radiative forcing remains scarce for globally prevalent macroalgae, mixed vegetation, and surrounding depositional sediment habitats. Here we show that these habitats emit CH₄ in the range of 0.1 - 2.9 mg CH₄ m^-2 d^-1 to the atmosphere, revealing in situ CH₄ emissions from macroalgae that were sustained by divergent methanogenic archaea in anoxic microsites. Over an annual cycle, CO₂-equivalent CH₄ emissions offset 28 and 35% of the carbon sink capacity attributed to atmospheric CO₂ uptake in the macroalgae and mixed vegetation habitats, respectively, and augment net CO₂ release of unvegetated sediments by 57%. Accounting for CH₄ alongside CO₂ sea-air fluxes and identifying the mechanisms controlling these emissions is crucial to constrain the potential of coastal ecosystems as net atmospheric carbon sinks and develop informed climate mitigation strategies.

SUBMITTER: Roth F

PROVIDER: S-EPMC9810657 | biostudies-literature | 2023 Jan

REPOSITORIES: biostudies-literature

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Methane emissions offset atmospheric carbon dioxide uptake in coastal macroalgae, mixed vegetation and sediment ecosystems.

Roth Florian F Broman Elias E Sun Xiaole X Bonaglia Stefano S Nascimento Francisco F Prytherch John J Brüchert Volker V Lundevall Zara Maysoon M Brunberg Märta M Geibel Marc C MC Humborg Christoph C Norkko Alf A

Nature communications 20230103 1

Coastal ecosystems can efficiently remove carbon dioxide (CO2) from the atmosphere and are thus promoted for nature-based climate change mitigation. Natural methane (CH4) emissions from these ecosystems may counterbalance atmospheric CO2 uptake. Still, knowledge of mechanisms sustaining such CH4 emissions and their contribution to net radiative forcing remains scarce for globally prevalent macroalgae, mixed vegetation, and surrounding depositional sedi ...[more]

PMID: 36596795

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Project description:Coastal freshwater wetlands are critical ecosystems for both local and global carbon cycles, sequestering substantial carbon while also emitting methane (CH4) due to anoxic conditions. Estuarine freshwater wetlands face unique challenges from fluctuating water levels, which influence water quality, vegetation, and carbon cycling. However, the response of CH4 fluxes and their drivers to altered hydrology and vegetation remains unclear, hindering mechanistic modeling. To address these knowledge gaps, we studied an estuarine freshwater wetland in the Great Lakes region, where rising water levels led to a vegetation shift from emergent Typha dominance in 2015-2016 to floating-leaved species in 2020-2022. Using eddy covariance flux measurements during the peak growing season (June-September) of both periods, we observed a 60% decrease in CH4 emissions, from 81 ± 4 g C m-2 in 2015-2016 to 31 ± 3 g C m-2 in 2020-2022. This decline was driven by two main factors: (1) higher water levels, which suppressed ebullitive fluxes via increased hydrostatic pressure and extended CH4 residence time, enhancing oxidation potential in the water column; and (2) reduced CH4 conductance through plants. Net carbon dioxide (CO2) uptake decreased by 90%, from -267 ± 26 g C m-2 in 2015-2016 to -27 ± 49 g C m-2 in 2020-2022. Additionally, diel CH4 flux patterns shifted, with a distinct morning peak observed in 2015-2016 but absent in 2020-2022, suggesting changes in plant-mediated transport and a potential decoupling from photosynthesis. The dominant factors influencing CH4 fluxes shifted from water temperature and gross primary productivity in 2015-2016 to atmospheric pressure in 2020-2022, suggesting an increased role of ebullition as a primary transport pathway. Our results demonstrate that changes in water levels and vegetation can substantially alter CH4 and CO2 fluxes in coastal freshwater wetlands, underscoring the critical role of hydrological shifts in driving carbon dynamics in these ecosystems.

Dataset Information

Methane emissions offset atmospheric carbon dioxide uptake in coastal macroalgae, mixed vegetation and sediment ecosystems.

Publications

Methane emissions offset atmospheric carbon dioxide uptake in coastal macroalgae, mixed vegetation and sediment ecosystems.

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