Created coastal wetlands as carbon stores: potential challenges and opportunities

Mossman, Hannah ORCID: https://orcid.org/0000-0001-5958-5320, Sullivan, Martin ORCID: https://orcid.org/0000-0002-5955-0483, Dunk, Rachel ORCID: https://orcid.org/0000-0002-8066-6763, Pemberton, Robert ORCID: https://orcid.org/0000-0003-0756-0150, Rae, stuart, Tempest, James and Pontee, Nigel (2022) Created coastal wetlands as carbon stores: potential challenges and opportunities. In: Challenges in Estuarine and Coastal Science: Estuarine and Coastal Sciences Association 50th Anniversary Volume. Pelagic Publishing, pp. 146-159. ISBN 9781784272852 (paperback); 9781784272869 (ebook)

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Abstract

Intertidal habitats are widely created with the aim of benefiting biodiversity. The pressing need to mitigate greenhouse gas emissions and the increasing recognition that coastal wetlands can provide secondary benefits by storing carbon may provide additional incentives for their creation. However, there are a number of uncertainties in the carbon budget of these wetlands, including the magnitude of carbon accumulation and the relative scale of this compared with the carbon costs of site construction. Here, we explore the carbon accumulation potential of hypothetical intertidal wetland sites of different sizes and shapes created by managed realignment and made with construction material sourced from different locations. We combine different combinations of values of sedimentation and carbon content reported from created intertidal wetlands in the literature. We find that there is large variability in potential carbon accumulation rates, with sedimentation rates being the dominant control on carbon accumulation. When carbon accumulation rates are high, all hypothetical site designs paid off the carbon cost of embankment construction within a year, but when carbon accumulation rates were low and material for embankments was transported from off site, debts took about ten years to pay. Our analysis provides a broad indication of the balance between carbon accumulation and construction carbon costs in created intertidal wetlands, but further work is needed to develop a more complete carbon budget. We highlight five key research challenges that need to be addressed to better understand the potential for created intertidal wetlands to accumulate carbon.