Blue carbon audit of Orkney waters

Porter, Joanne; Austin, William; Burrows, Michael; Clarke, Duncan; Davies, Gareth; Kamenos, Nick; Riegel, Simone; Smeaton, Craig; Page, Christopher; Want, Andrew

Abstract

In May 2019, the Scottish Government declared a global climate emergency in response to climatic change linked to elevated CO2 levels in the atmosphere. The most obvious effects of climate change include increased atmospheric and sea surface temperatures, ocean acidification, and greater occurrences of {\textquoteleft}extreme{\textquoteright} weather events. While the world{\textquoteright}s ocean forms the largest natural {\textquoteleft}sink{\textquoteright} for carbon, the rate of capture and storage in sea water is reduced by increasing levels of atmospheric CO2, rising global temperatures, and stratification of the surface ocean.The term {\textquoteleft}blue carbon{\textquoteright} has been used to describe carbon stored in the marine environment. As part of the Scottish Government{\textquoteright}s objectives to lead the world in adopting evidence-based policies to mitigate climate change, an audit of blue carbon resources has been commissioned for the waters around the Orkney Islands archipelago. This report is the most comprehensive regional audit of blue carbon resources to date.Blue carbon refers to carbon captured by biological metabolic processes, i.e. in the soft tissues, shells, and skeletons of plants and animals, and buried in the marine environment in sediment. In some regions this may also include carbon of terrigenous origin. In this audit, the evaluation of carbon storage includes shallow habitats created by marine organisms, and also, the resources stored in surface marine sediments. Once living tissue dies, the resulting organic carbon in biological material may be transported, and ultimately deposited and accumulated in seabed sediments. Carbon stocks in sediments that accumulate in this fashion may remain stored over far longer time scales, for example in the hundreds of years to thousands of years and in much larger amounts than stocks found in biological habitats, although the longevity of certain biological features, such as reefs, is poorly understood.Currently, detailed understanding of blue carbon capture and storage is limited to a few, relatively well-studied coastal ecosystems, including mangroves, saltmarshes and seagrass beds. In Scotland few published papers report on the contribution of marine habitats to blue carbon.The Orkney Blue Carbon Audit was conducted using a four-stage approach: 1) assessment of habitat abundance based on data collected during in situ surveys; 2) mapping of areas of known habitats compiled from various data sources to inform habitat prediction models; 3) determination of carbon content for specific habitats based on recent and current in situ sample collection and laboratory analysis; 4)3calculation of total organic and inorganic carbon contribution by combining areas and estimated carbon content of known habitats. Methods developed here will help inform similar studies as part of future audits of regional marine resources.Key blue carbon habitats evaluated in this audit included a wide variety of biological and sedimentary environments. The Orkney Blue Carbon Audit estimated 67 million tonnes (Mt) of blue carbon resources in Orkney, composed of 5.9 Mt in biological stocks and 2.27 Mt organic carbon and 59. 1 Mt the figure for inorganic carbon will increase in future when data gaps on the thickness of sediment deposits underlying biological habitats are addressed (e.g. horse mussel beds, flame shell beds, brittlestar beds, maerl beds) along with information on the extent of shell banks. Organic carbon stock figures are also likely to increase as there are stocks of organic carbon associated with inorganic carbon and trapped in the anoxic layers where carbon becomes recalcitrant.In biological habitats in Orkney, the most important stocks of blue carbon are found in maerl beds, kelp forest, and seagrass beds (Zostera). In particular, maerl beds had the highest contribution of blue carbon to the audit as well as having the highest density of carbon (tonnes per hectare1). New research generated for this report has provided greater details on carbon stocks in several habitats, such as saltmarsh, brittlestar beds, and bryozoan thickets.Knowledge gaps have been identified and suggestions made to prioritise future research. Additional habitat surveys and sample analysis will further reduce uncertainty in evaluating carbon resources. {\textquoteleft}Ground-truthing{\textquoteright} will improve predicted habitat models in locations where real data are not currently available.While uncertainties remain, the general conclusions presented here on blue carbon resources in Orkney waters are robust. The audit will inform the Orkney Islands Marine Region: State of the Environment Assessment. The extent to which blue carbon issues could be addressed as part of the statutory regional marine planning process will need to be considered through engagement with stakeholders and public consultation.Informed management could enhance the capacity of key habitats in providing a carbon sink, while at the same time encouraging sustainable use of the marine environment.

Citation

Porter, J., Austin, W., Burrows, M., Clarke, D., Davies, G., Kamenos, N., …Want, A. (2020). Blue carbon audit of Orkney waters. Aberdeen: Marine Scotland Science. https://doi.org/10.7489/12262-1

• Publication Date: 2020-02
• Deposit Date: Dec 15, 2022
• Publicly Available Date: Jan 18, 2023
• Series Title: Scottish Marine and Freshwater Science reports
• Series Number: 11.3
• DOI: https://doi.org/10.7489/12262-1
• Keywords: Carbonate system; Blue carbon; Marine environment; Marine ecosystems; Climate change
• Public URL: https://hull-repository.worktribe.com/output/4152638