What potential do Welsh Marine Protected Areas have for sequestering and storing carbon, and what are the implications for mitigating climate change?

Our oceans play a vital role in the global carbon cycle, with coastal and marine habitats acting as one of the largest natural sinks of carbon globally. Quantifying the carbon stored and sequestered (captured and added to standing stock) in these habitats is the first step in understanding their contribution towards mitigating climate change.

Blue carbon in context

Carbon sequestered and stored in marine ecosystems is known as ‘blue carbon’.

Blue carbon occurs within a range of habitat types, covering biological and geological components, such as saltmarshes and seagrass beds, biogenic reefs, and marine sediments over short to long timescales.

With ever increasing carbon dioxide and other greenhouse gas concentrations driving global climate change, there is a growing need to understand how marine habitats can facilitate climate change mitigation.

The estimation of carbon stocks and sequestration in marine habitats has received increasing attention in recent years. The first national scale assessment was undertaken by Burrows et al. (2014),⁽²⁾ who estimated Scotland’s blue carbon stocks. This audit remains a primary source of information for habitat-specific estimates. Since then, attention has been paid specifically to carbon storage in UK shelf sea sediments⁽⁴⁾⁽⁵⁾ and within Marine Protected Area (MPA) networks.^(1)(3)(6)

The blue carbon potential of Welsh MPAs

MPAs provide valuable protection to marine habitats, including blue carbon habitats, ranging from biological and geological components, such as saltmarshes and seagrass beds, to biogenic reefs and marine sediments.

Understanding the contribution MPAs make toward blue carbon, when making management decisions, could help better protect these habitats. This, in turn, could further enhance their capacity to provide carbon sink and promote the storage of carbon in the marine environment.

In Wales, MPAs cover approximately 69% of the Welsh inshore waters. There are 139 MPAs in Welsh waters, made up of:

• 15 Special Areas of Conservation (SACs)
• 13 Special Protection Areas (SPAs)
• 1 Marine Conservation Zone (MCZ)
• 107 Sites of Special Scientific Interest (SSSIs)
• 3 Ramsar sites

It is estimated that more than 99 km² of blue carbon habitat is located within the MPA network in Wales, and over 77 km² of these occur within the 15 SACs, designated to protect Annex I features under the 2017 Habitats Regulations. Most of these Annex I features contain sedimentary and/or biogenic habitats, known to sequester and store carbon.

In 2020, NRW published an evidence report, prepared by ABPmer, which revealed the blue carbon potential for Welsh marine sedimentary and biogenic habitats. The report found that at least 113 Mt of carbon are stored in the top 10 cm of the Welsh marine sediments, and an estimated 26,100 tonnes of carbon (0.03 Mt C) are sequestered each year.

Earlier this year, NRW commissioned ABPmer to prepare a second study (comprising a primary and supplementary report) to increase understanding of the blue carbon resources in Wales’ SAC network, by quantifying the contribution of the network to carbon storage and sequestration.

The key objectives were:

• To review the most recent literature on carbon storage and sequestration for different marine habitats in Wales
• To determine the spatial extent of Annex I features in the Welsh marine SAC network
• To estimate the carbon storage and sequestration potential of Annex I features in the network

In addition, the study identified management actions that could promote the carbon storage and sequestration of blue carbon habitats and the policy and regulatory pathways for implementing management in Welsh SACs.

Understanding the potential

The blue carbon potential of Welsh Annex I features was estimated using the most relevant literature values for carbon storage and sequestration, and calculating the habitat extents within each SAC Annex I feature.

The total contribution of Welsh SAC Annex I features to carbon storage was estimated to be 11 Mt of carbon in the top 10 cm of sediment, accounting for almost 10% of the total carbon storage across all habitats in the WNMP area.

The rate of sequestration was approx. 12,300 t of carbon per year across the SAC network, accounting for 47% of the total carbon sequestered within Welsh habitats.

Annex I features that cover larger spatial extents, such as estuaries and large shallow inlets and bays, contribute the most towards carbon storage and sequestration across the network, while designated saltmarshes contribute the most towards blue carbon per unit area.

Management, policy and regulatory frameworks

Protection of blue carbon habitats by managing known pressures was found to be a common management tool if used with the potential to enhance blue carbon stocks. Habitat creation and restoration schemes have also been used for saltmarsh, seagrass and shellfish beds, and the success of these schemes relies on careful planning (including assessments, consents and timing of project) and management of potential pressures.

To promote blue carbon storage and sequestration in Wales, it was suggested that more emphasis could be included on the importance of blue carbon habitats within the Regulation 37 Conservation Objectives of SACs. This then has the potential to feed into the advice for operations to highlight those which may cause deterioration or disturbance to blue carbon habitats.

Conclusion and implications

Vegetated coastal habitats such as saltmarshes, seagrasses and kelp have a relatively small spatial extent in Welsh waters, however, SACs often protect features which cover large areas of vegetated coastal habitats. As such, SACs account for a high proportion of total carbon sequestered in Welsh marine habitats every year.

To download the full report, visit the NRW website.

Download the supplementary report here.

ABPmer routinely advises marine sectors on regulatory and policy matters and has a long history supporting government and its agencies in developing the evidence base against which policy decisions are made.

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References

^{(1)^ Burrows MT, Hughes DJ, Austin WEN, Smeaton C, Hicks N, Howe JA, Allen C, Taylor P. Vare LL. 2017. Assessment of Blue Carbon Resources in Scotland’s Inshore Marine Protected Area Network. Scottish Natural Heritage Commissioned Report No. 957.}

^{(2)^ Burrows MT, Kamenos NA, Hughes DJ, Stahl H, Howe JA, Tett P. 2014. Assessment of carbon budgets and potential blue carbon stores in Scotland’s coastal and marine environment. NatureScot Commissioned Report No. 761.}

^{(3)^ Burrows MT, Moore P, Sugden H, Fitzsimmons C, Smeaton C, Austin W, Parker R, Kröger S, Powell C, Gregory L, Procter W, Brook T. 2021. Assessment of Carbon Capture and Storage in Natural Systems within the English North Sea (Including within Marine Protected Areas). A North Sea Wildlife Trusts, Blue Marine Foundation, WWF and RSPB commissioned report.}

^{(4)^ Diesing M, Kröger S, Parker R, Jenkins C, Mason C, Weston K. 2017. Predicting the standing stock of organic carbon in surface sediments of the North–West European continental shelf. Biogeochemistry 135 (1), 183-200./sup>}

^{(5)^ Smeaton C, Hunt CA, Turrell WR, Austin WE. 2021. Marine Sedimentary Carbon Stocks of the United Kingdom’s Exclusive Economic Zone. Frontiers in Earth Science 9, 50.}

^{(6)^ Strong JA, Mazik K, Piechaud N, Bryant L, Wardell C, Hull S, Tickle M, Norrie E-M, McIlvenny H, Clements A. 2021. Blue carbon restoration in Northern Ireland –feasibility study. Agriculture, Environment and Rural Affairs and Ulster Wildlife.}