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Geomorphic and ecological constraints on the coastal carbon sink

Nature Reviews Earth & Environment volume 4, pages 393–406 (2023)Cite this article

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An Author Correction to this article was published on 02 April 2024

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Abstract

Climate change is driving a fundamental reorganization of the coastal zone, in which carbon-rich ecosystems are simultaneously migrating, accreting and submerging. In this Review, we discuss the geomorphic processes constraining soil carbon accumulation and the ecological processes constraining greenhouse gas emissions that together determine the net radiative forcing of the coastal landscape and the size of the coastal carbon sink. Sea level rise creates vertical and lateral accommodation space that potentially enhances soil carbon accumulation in marshes and mangroves. However, sea level rise and saltwater intrusion lead to ecosystem transitions that result in loss of existing carbon pools, altering the balance between carbon sequestration and greenhouse gas emissions. We propose that ecosystem reorganization results in large, but mostly offsetting, changes in radiative forcing. At the continental scale, losses in soil carbon sequestration and wood production are offset by reduced methane emissions associated with salinization of freshwater ecosystems. Nevertheless, climate effects on the coastal carbon sink remain largely studied within individual ecosystems. Future work is needed to determine the connectivity of carbon between ecosystems, changes in carbon accumulation and greenhouse gas emissions as ecosystem transitions occur, and the fate of carbon as it moves through the coastal landscape.

Key points

  • Sea level rise is driving the reorganization of coastal ecosystems and has substantial consequences for the fate of the coastal carbon sink.

  • Geomorphic processes drive soil carbon accumulation, whereas ecological processes drive greenhouse gas emissions and changes in wood production.

  • Sea-level-driven losses in carbon accumulation (12 Tg CO2eq yr−1) are roughly offset by reduced methane emissions associated with salinization (−13 Tg CO2eq yr−1) across the continental United States.

  • Future work is needed to improve the connection between carbon sequestration and greenhouse gas emissions across a thoroughly connected coastal landscape.

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Fig. 1: Simplified view of the coastal carbon sink.
Fig. 2: Influence of sea level rise on wetland soil carbon accumulation.
Fig. 3: Historical land loss in coastal Louisiana and implications for landscape-scale carbon budgets.
Fig. 4: Examples of how interacting global change drivers offset effects on ecosystem-level carbon sequestration.
Fig. 5: Radiative forcing as a consequence of ecosystem state change.

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Acknowledgements

Funding for this project was provided by the US Department of Energy, Office of Science, Office of Biological and Environmental Research, Environmental System Science programme (DE-SC0014413, DE-SC0019110 and DE-SC0021112), and through the COMPASS-FME project (DE-AC05-76RL01830). J.P.M. and G.L.N. acknowledge support from the Smithsonian Institution. M.L.K. and A.J.S. acknowledge support from the National Science Foundation (#1654374, 1832221 and 2012670) and the USGS Ecosystem Land Change Science Program.

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  1. Virginia Institute of Marine Science, William & Mary, Gloucester Point, VA, USA

    Matthew L. Kirwan & Alexander J. Smith

  2. Smithsonian Environmental Research Center, Edgewater, MD, USA

    J. Patrick Megonigal & Genevieve L. Noyce

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J.P.M. and A.J.S. researched data for the article. All authors wrote the article, made a substantial contribution to discussion of content, and reviewed and/or edited the manuscript before submission.

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Kirwan, M.L., Megonigal, J.P., Noyce, G.L. et al. Geomorphic and ecological constraints on the coastal carbon sink. Nat Rev Earth Environ 4, 393–406 (2023). https://doi.org/10.1038/s43017-023-00429-6

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