Preprints
https://doi.org/10.5194/egusphere-2025-3293
https://doi.org/10.5194/egusphere-2025-3293
22 Jul 2025
 | 22 Jul 2025
Status: this preprint is open for discussion and under review for Biogeosciences (BG).

Carbon sequestration along a gradient of tidal marsh degradation in response to sea level rise

Mona Huyzentruyt, Maarten Wens, Gregory Scott Fivash, David C. Walters, Steven Bouillon, Joell A. Carr, Glenn C. Guntenspergen, Matthew L. Kirwan, and Stijn Temmerman

Abstract. Tidal marshes are considered one of the world’s most efficient ecosystems for belowground organic carbon sequestration and hence climate mitigation. Marsh systems are however also vulnerable to degradation due to climate-induced sea level rise, whereby marsh vegetation conversion to open water often follows distinct spatial patterns: levees (i.e. marsh zones <10 m from tidal creeks) show lower vulnerability of vegetation conversion to open water than basins (i.e. interior marsh zones >30 m from creeks). Here, we use sediment cores to investigate spatial variations in organic carbon accumulation rates (OCAR) in a microtidal system (Blackwater marshes, Maryland, USA): (1) across a gradient of marsh zones with increasing marsh degradation, assessed as increasing ratio of unvegetated versus vegetated marsh area and (2) by comparing levees versus basins. We show that OCAR is up to four times higher on marsh levees than in adjacent basins. The data suggest that this is caused by spatial variation in three processes: sediment accretion rate, vegetation productivity, and sediment compaction, which are all higher on levees. Additionally, OCAR was observed to increase with increasing degree of marsh degradation in response to sea level rise. We hypothesize this may be due to more soil waterlogging in more degraded marsh zones, which may decrease carbon decomposition. Our results highlight that tidal marsh levees, in a microtidal system, are among the fastest soil organic carbon sequestration systems on Earth, and that both levees and basins sustain their carbon accumulation rate along gradients of increasing marsh degradation in response to sea level rise.

Competing interests: At least one of the (co-)authors is a member of the editorial board of Biogeosciences.

Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this paper. While Copernicus Publications makes every effort to include appropriate place names, the final responsibility lies with the authors. Views expressed in the text are those of the authors and do not necessarily reflect the views of the publisher.
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Mona Huyzentruyt, Maarten Wens, Gregory Scott Fivash, David C. Walters, Steven Bouillon, Joell A. Carr, Glenn C. Guntenspergen, Matthew L. Kirwan, and Stijn Temmerman

Status: open (until 15 Sep 2025)

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Mona Huyzentruyt, Maarten Wens, Gregory Scott Fivash, David C. Walters, Steven Bouillon, Joell A. Carr, Glenn C. Guntenspergen, Matthew L. Kirwan, and Stijn Temmerman
Mona Huyzentruyt, Maarten Wens, Gregory Scott Fivash, David C. Walters, Steven Bouillon, Joell A. Carr, Glenn C. Guntenspergen, Matthew L. Kirwan, and Stijn Temmerman

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Short summary
Vegetated environments from forests to peatlands store carbon in the soil, which mitigates climate change. But which environment does this best? In this study, we show how the levees of tidal marshes are one of the most effective carbon sequestering environments in the world. This is because soil water-logging and high salinity inhibits carbon degradation while the levee fosters fast vegetation growth, complimented also by the preferential settlement of carbon-rich sediments on the marsh levee.
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