Accelerating saltmarsh restoration with private finance via the voluntary carbon market

Since the mid-1800s the UK has lost a considerable amount of saltmarsh, mostly due to land claim for agricultural use, resulting in loss of vital coastal habitat, a nature-based sea defence and release of greenhouse gases (GHGs) into the atmosphere. Restoring and recreating these habitats could play an effective role in climate change mitigation by trapping and storing atmospheric carbon, with added benefits to coastal defence, biodiversity and water quality.

Financing large-scale restoration is becoming more viable, as businesses become more motivated to voluntarily offset CO2 emissions via the voluntary carbon market.

UKCEH is leading a consortium across charity, finance and academic sectors to develop and pilot a UK Saltmarsh Carbon Code. This rigorous and scientifically-based voluntary certification standard will enable saltmarsh carbon to be confidently purchased, thus providing an income stream for restoration projects and supporting the achievement of national Net Zero goals.

Project timeline

Project timeline. Phase 1 is evidence gathering, feasibility study and recommendations. Phase 2 includes 2a Drafting the code and 2b Refining the code

Phase 1 - completed in January 2023 – was funded by Natural Environment Investment Readiness Fund (NEIRF) and included:

  • A feasibility analysis of the Verified Carbon Standard VM0003 vs. a UK code
  • Recommendations on the best way forward to develop a fully operational UK domestic Saltmarsh Code
  • Two systemic evidence reviews on saltmarsh blue carbon and GHGs for northwest Europe and globally (made possible with additional funding from Blue Marine Foundation and WWT)

Phase 2 – funded by Defra through the Environment Agency – is currently underway with an expected completion date of summer 2025.

Phase 2a will draft the pilot code, which will include:

  • A critical scientific synthesis to inform accuracy and functioning of the Saltmarsh Code with Measurement, Reporting, and Verification (MRV) development
  • Code design with all documentation and tools compiled
  • Establishment of code management and governance including host, registry and validation and verification bodies (VVB)

Phase 2b will test the pilot code and use recommendations to further refine the code. During this stage business and finance models will also be developed.

Outputs and key findings

Saltmarsh restoration

Evidence Synthesis of Saltmarsh Blue Carbon in the UK and NW Europe (2022)

The report presents a comprehensive and robust assessment of the evidence quantifying blue carbon in natural UK and NW European saltmarshes, as well as the first comprehensive estimate for restored sites. Our results point to the importance of considering full greenhouse gas fluxes when considering net carbon benefit of restored marshes, while highlighting the potential of saltmarsh restoration to not only enhance biodiversity, but also to play a role in future efforts to mitigate climate change.

  1. Newly restored marshes have a high rate of C sequestration (13.3 ± 15.0 t CO2e ha-1 year-1), however there is a lack of data on how older restored marshes might differ.
  2. Restored saltmarshes act as a net source of nitrous oxide, whereas natural marshes act as a net sink, indicating a need to include greenhouse gas fluxes into potential carbon burial budgets of restored saltmarshes.
  3. More research is required on the influence of saltmarsh characteristics (eg. pH, salinity, vegetation, sediment type) on the carbon and greenhouse gas fluxes of restored saltmarshes.



Evidence Synthesis of Blue Carbon Benefits from global saltmarsh restoration (2023)

We screened over 29000 studies and analysed data from 431 to quantify carbon storage and greenhouse gas emissions of ‘natural’ and ‘restored’ saltmarshes on a global scale. Incorporating greenhouse gas fluxes into our estimates allowed a ‘net carbon benefit’ of restoration to be calculated, highlighting the need to consider carbon uptake as well as release to arrive at a more balanced estimate of climate change mitigation potential. 

  1. Global marshes store approximately 1.41–2.44 Pg carbon
  2. Restored marshes had very low greenhouse gas fluxes and rapid carbon accumulation, resulting in a mean net accumulation rate of 64.70 t CO2e ha−1 year−1.
  3. Saltmarsh regeneration could result in 12.93–207.03 Mt CO2e accumulation per year, offsetting the equivalent of up to 0.51% global energy-related CO2 emissions



Feasibility study of VCS VM0033 (2023)

This report assesses the feasibility of using the Verified Carbon Standard (VCS) VM0033 Methodology for Tidal Wetland and Seagrass Restoration (version 2) in a UK context. From the analysis presented in the report, the authors conclude VM0033 could be applied to saltmarsh restoration via managed realignment (MR) in the UK, and that it allows for UK (or site/region) specific estimates of GHG reductions or removals by using the most appropriate method to match available data and current knowledge. However, the illustrative investment cases suggest VM0033 is not a commercially viable option. This is due to high upfront costs to projects compared to those estimated for a UK domestic Saltmarsh Code (assuming similarities to the Woodland Carbon Code (WCC) and Peatland Code (PC)).

Key reasons for the recommendation of a UK domestic Saltmarsh Code:

  1. Greater commercial viability due to the decreased upfront costs to projects entering the code
  2. Alignment of key aspects with the other UK domestic codes (WCC and PC), ensuring consistency within the market.
  3. The ability to streamline methodology to address restoration of saltmarsh habitat via MR in the UK only.



Recommendations for development of a UK domestic Saltmarsh Code (2023)

This report describes recent developments in the UK voluntary carbon market to provide background to the space in which the Code would operate and gives detailed thought to key elements such as eligibility, additionality, permanence, and leakage. The report identifies several key gaps that need to be filled to support the facilitation of the Saltmarsh Code:

  1. Quantitative empirical evidence behind carbon accumulation and sequestration rates remains scarce and needs to be improved
  2. Drivers that control net rates over time need to be identified
  3. Identification of predictor variables (or ‘proxies’) to estimate or model carbon gain or loss in restoration sites would decrease MRV costs

Long-term vision

The Saltmarsh Code as it is currently developed will focus on carbon credits for managed realignment (MR) projects only because this is what the scientific evidence currently supports. However, saltmarshes are valuable habitats providing many more benefits than just carbon storage. They also play crucial roles in supporting biodiversity, providing flood defence and filtering out nutrients. The current Saltmarsh Code framework can be amended in the future to include credits for the stacked benefits that these coastal habitats provide.

As well as potentially including these other benefits, our vision for the Saltmarsh Code is for it to also include other restoration activities (for example use of polders, blocking channels, beneficial use of dredged material (BUIDS)), once knowledge on the benefits of these are better understood. We feel incorporating these smaller-scale, quicker to implement, restoration techniques is essential to unlocking greater potential for saltmarsh to contribute to climate change mitigation.

Contact the UKCEH team


The consortium includes Bangor University, SRUC (Scotland’s Rural College), WWT (Wildfowl and Wetlands Trust), RSPB (Royal Society for the Protection of Birds), University of St Andrews, Finance Earth, IUCN National Committee UK and Jacobs.


Phase 1 of the project was funded through the Natural Environment Investment Readiness Fund (NEIRF) from October 2021–September 2022. The NEIRF, designed by Defra and the Environment Agency, aims to stimulate private investment to improve and safeguard our natural environment. The fund will develop innovative nature projects that provide both environmental benefits and can attract private investment, helping them get ready for investment and therefore creating a pipeline between projects and the private sector.

The work on the literature reviews in Phase 1 continued thanks to co-funding from the Wildfowl & Wetlands Trust and the Blue Marine Foundation.

Phase 2 of the project is funded by the Environment Agency and Defra.