Alkalinity Production Coupled to Pyrite Formation Represents an Unaccounted Blue Carbon Sink

Reithmaier, Gloria Maria Susanne; Johnston, Scott G; Junginger, Tobias; Goddard, Madeline M; Sanders, Christian J.; Hutley, Lindsay B.; Ho, David T.; Maher, Damien T.

doi:10.1029/2020gb006785

Cited by 29 publications

(26 citation statements)

References 102 publications

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“…Both aerobic and anaerobic diagenetic processes produce DIC whereas only anaerobic degradation of organic matter such as denitrification and sulfate reduction drive significant total alkalinity (TA) generation in coastal sediments (Reithmaier et al 2021). The balance between DIC and TA influences the marine inorganic carbon budget, affecting whether carbon will evade as atmospheric CO 2 or accumulate in the ocean as bicarbonate and carbonate (Andersson et al 2006;Hu and Cai 2011).…”

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Alkalinity export to the ocean is a major carbon sequestration mechanism in a macrotidal saltmarsh

Yau

Xin

Chen

et al. 2022

Limnology & Oceanography

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Saltmarshes are a blue carbon ecosystem accumulating large quantities of organic carbon in sediments. Some of this carbon can be transformed into dissolved inorganic carbon (DIC) and methane (CH 4 ) that may eventually be exported to the ocean or atmosphere. Although extensive studies have quantified specific components of the carbon budget such as carbon burial, limited attention has been given to pore-water-derived carbon and total alkalinity (TA) exports to the ocean. Here, we quantified lateral exports to the ocean (outwelling) of 202 AE 160 and 78 AE 75 mmol m À2 d À1 of DIC and TA, respectively. The TA : DIC concentration ratio in the creek waters was $ 1, implying TA production from anaerobic mineralization in sediments. The lateral TA exports were comparable to the local (94 AE 48 mmol m À2 d À1 ) and national ($ 50 mmol m À2 d À1 ) organic carbon burial. High TA exports could locally increase the ocean buffering capacity and contribute bicarbonate to the coastal ocean, acting as a long-term carbon storage. Pore water traced by radon contributed 28-37% and 58-69% of DIC and TA exports. Separating the two major DIC components (i.e., CO 2 emissions and alkalinity exports) is essential to resolve the carbon sequestration potential from saltmarshes. Here, dissolved CO 2 emissions to the atmosphere accounted for 3-5% of total DIC outwelling. CH 4 emissions played a minor role offsetting around 0.3 to 6% of the carbon sequestration. Overall, we demonstrate that alkalinity export into the ocean can be an overlooked carbon sequestration pathway in saltmarshes at rates comparable to carbon burial.

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confidence: 99%

Alkalinity export to the ocean is a major carbon sequestration mechanism in a macrotidal saltmarsh

Yau

Xin

Chen

et al. 2022

Limnology & Oceanography

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“…8 The lower salinity may influence soil functions including pollutant retention, carbon sequestration, and greenhouse gas emissions, since pyritization is directly linked to these functions. 9 For example, even mangrove systems with high salinities likely emit some level of methane, 10 emission rates in these low salinity forests may be expected to be even greater. The distinct soil properties of this coastal region further set the stage for the diverse plant species found in this atypical mangrove setting, of which has not yet been observed in any other region of the world.…”

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The novel mangrove environment and composition of the Amazon Delta

et al. 2022

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“…These pathways differ in the form of organic carbon sequestered (dissolved or particulate), as well as in the physical, biological, and chemical processes with which they interact. Other pathways, such as the permanent reduction of metabolic products formed via alkalinity production have been proposed, but remain poorly understood in macroalgae systems (Reithmaier et al ., 2021; Perkins et al ., 2022).…”

Section: Main Macroalgal Carbon Sequestration Pathwaysmentioning

confidence: 99%

“…cloud formation, albedo), and consideration of other biogeochemical processes that regulate CO 2 fluxes, such as those producing or consuming alkalinity. These are only just receiving attention, as showing additionality and permanence of these processes is more challenging than for those already discussed (Reithmaier et al ., 2021). The production and export of alkalinity is increasingly viewed as a significant CO 2 sink that complements the previously described organic carbon sequestration potential of blue carbon ecosystems (Reithmaier et al ., 2021; Perkins et al ., 2022).…”

Section: Mapping Macroalgal Carbon Sequestration Potential and Direct...mentioning

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Carbon sequestration and climate change mitigation using macroalgae: a state of knowledge review

et al. 2023

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The conservation, restoration, and improved management of terrestrial forests significantly contributes to mitigate climate change and its impacts, as well as providing numerous co‐benefits. The pressing need to reduce emissions and increase carbon removal from the atmosphere is now also leading to the development of natural climate solutions in the ocean. Interest in the carbon sequestration potential of underwater macroalgal forests is growing rapidly among policy, conservation, and corporate sectors. Yet, our understanding of whether carbon sequestration from macroalgal forests can lead to tangible climate change mitigation remains severely limited, hampering their inclusion in international policy or carbon finance frameworks. Here, we examine the results of over 180 publications to synthesise evidence regarding macroalgal forest carbon sequestration potential. We show that research efforts on macroalgae carbon sequestration are heavily skewed towards particulate organic carbon (POC) pathways (77% of data publications), and that carbon fixation is the most studied flux (55%). Fluxes leading directly to carbon sequestration (e.g. carbon export or burial in marine sediments) remain poorly resolved, likely hindering regional or country‐level assessments of carbon sequestration potential, which are only available from 17 of the 150 countries where macroalgal forests occur. To solve this issue, we present a framework to categorize coastlines according to their carbon sequestration potential. Finally, we review the multiple avenues through which this sequestration can translate into climate change mitigation capacity, which largely depends on whether management interventions can increase carbon removal above a natural baseline or avoid further carbon emissions. We find that conservation, restoration and afforestation interventions on macroalgal forests can potentially lead to carbon removal in the order of 10's of Tg C globally. Although this is lower than current estimates of natural sequestration value of all macroalgal habitats (61–268 Tg C year−1), it suggests that macroalgal forests could add to the total mitigation potential of coastal blue carbon ecosystems, and offer valuable mitigation opportunities in polar and temperate areas where blue carbon mitigation is currently low. Operationalizing that potential will necessitate the development of models that reliably estimate the proportion of production sequestered, improvements in macroalgae carbon fingerprinting techniques, and a rethinking of carbon accounting methodologies. The ocean provides major opportunities to mitigate and adapt to climate change, and the largest coastal vegetated habitat on Earth should not be ignored simply because it does not fit into existing frameworks.

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Alkalinity Production Coupled to Pyrite Formation Represents an Unaccounted Blue Carbon Sink

Cited by 29 publications

References 102 publications

Alkalinity export to the ocean is a major carbon sequestration mechanism in a macrotidal saltmarsh

Alkalinity export to the ocean is a major carbon sequestration mechanism in a macrotidal saltmarsh

The novel mangrove environment and composition of the Amazon Delta

Carbon sequestration and climate change mitigation using macroalgae: a state of knowledge review

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