Rapid carbon accumulation at a saltmarsh restored by managed realignment exceeded carbon emitted in direct site construction

Mossman, Hannah L. ORCID: https://orcid.org/0000-0001-5958-5320 , Pontee, Nigel, Born, Katie, Hill, Colin, Lawrence, Peter ORCID: https://orcid.org/0000-0002-9809-0221 , Rae, Stuart, Scott, James, Serato, Beatriz, Sparkes, Robert B. ORCID: https://orcid.org/0000-0003-0756-0150 , Sullivan, Martin J.P. ORCID: https://orcid.org/0000-0002-5955-0483 and Dunk, Rachel M. ORCID: https://orcid.org/0000-0002-8066-6763 (2022) Rapid carbon accumulation at a saltmarsh restored by managed realignment exceeded carbon emitted in direct site construction. PLoS ONE, 17 (11). e0259033.

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Abstract

Increasing attention is being paid to the carbon sequestration and storage services provided by coastal blue carbon ecosystems such as saltmarshes. Sites restored by managed realignment, where existing sea walls are breached to reinstate tidal inundation to the land behind, have considerable potential to accumulate carbon through deposition of sediment brought in by the tide and burial of vegetation in the site. While this potential has been recognised, it is not yet a common motivating factor for saltmarsh restoration, partly due to uncertainties about the rate of carbon accumulation and how this balances against the greenhouse gases emitted during site construction. We use a combination of field measurements over four years and remote sensing to quantify carbon accumulation at a large managed realignment site, Steart Marshes, UK. Sediment accumulated rapidly at Steart Marshes (mean of 75 mm yr-1) and had a high carbon content (4.4% total carbon, 2.2% total organic carbon), resulting in carbon accumulation of 36.6 t ha-1 yr-1 total carbon (19.4 t ha-1 yr-1 total organic carbon). This rate of carbon accumulation is an order of magnitude higher than reported in many other restored saltmarshes, and is somewhat higher than values previously reported from another hypertidal system (Bay of Fundy, Canada). The estimated carbon emissions associated with the construction of the site were ~2–4% of the observed carbon accumulation during the study period, supporting the view that managed realignment projects in such settings may have significant carbon accumulation benefits. However, uncertainties such as the origin of carbon (allochthonous or autochthonous) and changes in gas fluxes need to be resolved to move towards a full carbon budget for saltmarsh restoration.

Item Type:	Article
Journal / Publication Title:	PLoS ONE
Publisher:	Public Library of Science
ISSN:	1932-6203
Departments:	Institute of Science and Environment > Forestry and Conservation
Additional Information:	Peter J. Lawrence is a Lecturer in Geography at the Institute of Science & Environment, University of Cumbria, UK. ** Acknowledgements: We thank the Wildfowl and Wetlands Trust, particularly Alys Laver and Tim McGrath, for access to the site and their ongoing enthusiasm and support. We thank Grace Biddle and David McKendry for their work in the laboratory. This study uses data from UK National Tide Gauge Network, owned and operated by the Environment Agency, and provided by the British Oceanographic Data Centre. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Depositing User:	Insight Administrator
SWORD Depositor:	Insight Administrator
Date Deposited:	05 Dec 2022 10:00
Last Modified:	13 Jan 2024 14:16
URI:	https://insight.cumbria.ac.uk/id/eprint/6720

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