Global trends in air-water CO2 exchange over seagrass meadows revealed by atmospheric Eddy Covariance

Dam, Bryce Van; Polsenaere, Pierre; Barreras, Aylin; Lopes, Christian; Sánchez-Mejía, Z. M.; Tokoro, Tatsuki; Kuwae, Tomohiro; Gutiérrez-Loza, Lucía; Rutgersson, Anna

doi:10.1002/essoar.10504484.1

Cited by 2 publications

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“…The importance of including atmosphere–ocean CO 2 fluxes in estimations of carbon sequestration is also highlighted for seagrass systems, which are considered to be important blue carbon stocks: Measurements of atmosphere–ocean CO 2 fluxes indicate that seagrasses may sequester much less CO 2 than previous estimates based on sediment accretion rates alone (Van Dam et al. 2021). In summary, natural kelp beds are probably not in steady state for timescales relevant to CDR and carbon sequestration, and this needs to be carefully accounted for when calculating carbon offsets or credits.…”

Section: Forensic Carbon Accountingmentioning

confidence: 99%

Forensic carbon accounting: Assessing the role of seaweeds for carbon sequestration

Hurd

Law

Bach

et al. 2022

Journal of Phycology

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Carbon sequestration is defined as the secure storage of carbon‐containing molecules for >100 years, and in the context of carbon dioxide removal for climate mitigation, the origin of this CO2 is from the atmosphere. On land, trees globally sequester substantial amounts of carbon in woody biomass, and an analogous role for seaweeds in ocean carbon sequestration has been suggested. The purposeful expansion of natural seaweed beds and aquaculture systems, including into the open ocean (ocean afforestation), has been proposed as a method of increasing carbon sequestration and use in carbon trading and offset schemes. However, to verify whether CO2 fixed by seaweeds through photosynthesis leads to carbon sequestration is extremely complex in the marine environment compared to terrestrial systems, because of the need to jointly consider: the comparatively rapid turnover of seaweed biomass, tracing the fate of carbon via particulate and dissolved organic carbon pathways in dynamic coastal waters, and the key role of atmosphere–ocean CO2 exchange. We propose a Forensic Carbon Accounting approach, in which a thorough analysis of carbon flows between the atmosphere and ocean, and into and out of seaweeds would be undertaken, for assessing the magnitude of CO2 removal and robust attribution of carbon sequestration to seaweeds.

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Section: Forensic Carbon Accountingmentioning

confidence: 99%

Forensic carbon accounting: Assessing the role of seaweeds for carbon sequestration

Hurd

Law

Bach

et al. 2022

Journal of Phycology

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“…Seagrass meadows sequester carbon dioxide (CO 2 ) through photosynthesis (Van Dam et al, 2021) and trap allochthonous particles within their canopy (Gacia et al, 2002). Part of this carbon is then stored as biomass and as organic carbon in sediments for centuries and even millennia (Serrano et al, 2016(Serrano et al, , 2021.…”

Section: Introductionmentioning

confidence: 99%

Methane emissions in seagrass meadows as a small offset to carbon sequestration

Yau

Reithmaier²,

Majtenyi-Hill

et al. 2022

Preprint

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Seagrass meadows are effective carbon sinks due to their high primary production and sequestration in sediments. However, methane (CH4) fluxes can partially counteract their carbon sink capacity. Here, we measured diffusive sediment-water and air-sea CO2 and CH4 fluxes in a coastal embayment dominated by Posidonia oceanica in the Mediterranean Sea. High resolution timeseries observations revealed large spatial and temporal variability in CH4 concentrations (2 to 36 nM). Higher emissions were observed in an area with dense seagrass meadows. A 6 − 40% decrease of CH4 concentration in the surface water around noon indicates that photosynthesis likely limits CH4 fluxes. Sediments were the major CH4 source as implied from radon (a natural porewater tracer) observations and evidence for methanogenesis in deeper sediments. CH4 sediment-water fluxes (0.1 ± 0.1 − 0.4 ± 0.1 µmol m-2 d-1) were higher than average water-air CH4 emissions (0.12 ± 0.10 µmol m-2 d-1), suggesting that dilution and CH4 oxidation in the water column could reduce net CH4 fluxes into the atmosphere. Overall, relatively low air-sea CH4 fluxes at this likely represent net emissions from subtidal seagrass habitats sites, which are not influenced by nearby allochthonous CH4 sources. The local CH4 emissions in P. oceanica offset less than 1% of the carbon burial in sediments (142 ± 69 g CO2eq m-2 yr-1). Combining our results with earlier observations in other seagrass meadows worldwide reveals that global CH4 emissions within seagrass meadows only offset a small fraction (<2%) of carbon sequestration in sediments.

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Global trends in air-water CO2 exchange over seagrass meadows revealed by atmospheric Eddy Covariance

Cited by 2 publications

References 0 publications

Forensic carbon accounting: Assessing the role of seaweeds for carbon sequestration

Forensic carbon accounting: Assessing the role of seaweeds for carbon sequestration

Methane emissions in seagrass meadows as a small offset to carbon sequestration

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