Carbon Storage in Intertidal Environments (C-SIDE)

Lead Research Organisation: University of St Andrews
Department Name: Geography and Sustainable Development


The Earth's climate is warming and sea levels are rising around the globe, flooding and eroding our coasts. One important type of coastal environment that is at risk are saltmarshes. These are vegetated tidal flats that are tucked away in sheltered embayments, where there is a gradual transition between the land and sea. They also occur in more exposed locations where they form a natural defence against the encroaching sea. Saltmarshes are also valuable because the plants that grow on them absorb carbon at a very fast pace, much faster than, for example, trees. Saltmarshes are therefore useful in taking carbon out of the atmosphere and storing it away. Because carbon in the atmosphere is important in controlling the Earth's temperature, storing carbon in the ground can help reduce climate change.

The vegetation on a saltmarsh is close to the level of the highest tides. Every time the tide comes in, a thin layer of mud is deposited on top of the saltmarsh surface. Over time, the saltmarsh mud gets thicker, but it can only increase in thickness if sea level goes up. So in that sense, sea-level rise can be beneficial to saltmarshes, because if the amount of mud gets thicker they can perhaps store more carbon and reduce climate change further! It is a new idea. Whether it is actually true is what we want to find out.

As always, things aren't so simple. Apart from sea-level rise, there are other factors that can play a role in changing the amount of carbon buried in a saltmarsh, for example the tides, the availability of sediment, the types of plants, and whether the marsh is sheltered or exposed to the sea. We have picked 7 coastal regions in Britain that are all slightly different to analyse these different factors. Sea-level rise, the part we think is most important, is much faster in the south, where coasts are sinking, compared to Scotland, where the land is going up ever so slightly. We can treat Britain as a 'natural laboratory' to answer global questions: What controls carbon uptake in saltmarshes? Is sea-level rise beneficial? We expect that our studies will teach us lessons for saltmarshes around the world.

What will we do? We have designed our project into five parts. In part 1 we will look at the salt marsh mud in the past and present. We will measure how thick the mud is by coring and by running equipment which can 'see' below the ground. We will collect four cores at each of the 7 sites and use radioactive dating methods to tell us how old these sediments are. This is important because sea-level change has varied through time and rose much faster in the last 100 years than before. We will also measure the build-up of mud in the present day. In part 2 we will measure how much carbon is stored both above and below the ground. We will survey the plants which are growing on the marsh and then measure them further in the laboratory. We will measure the amount of carbon in the cores we collected, and do analyses to find out where the carbon came from (from the marsh vegetation itself or washed in with the tide). Experiments with buried tea bags will allow us to find out how much carbon is lost from dead plants during burial. And we will recruit members of the general public to help us with sampling so that we can cover more saltmarshes. We have an app for this. In part 3 and 4 we will gather data from various sources and multiply the data from our 7 sites to find out how representative our findings are for the whole of Britain. All saltmarshes will be mapped in 3 dimensions. We will collect data on all environmental factors and find out which ones can predict how much carbon is in saltmarshes using statistics and computer models. The final part 5 is all about the benefits of this project. We will use our results to recommend how managers of coastlines may be able to make use of saltmarshes to help fight climate change and sea-level rise, for example by establishing new saltmarshes on old coastal farmland.

Planned Impact

The following stakeholders and non-academic end-users of the C-SIDE project include: (i) Local and regional coastal partnerships/groups (e.g. Solway Firth Partnership, Solent Forum, East Anglia Coastal Group, etc.); (ii) national UK policy advice partners (e.g. Scottish Natural Heritage, Natural England, Natural Resources Wales, Defra, Crown Estate, RSPB); and (iii) international environmental organizations (e.g. UNEP, IPCC). These organisations will benefit from the first national-scale accounting of intertidal Blue Carbon resources, where the potential natural capital value of that resource can be framed within the context of environmental change (e.g. sea level rise) and existing coastal management plans. In addition, these organisations and the wider general public will benefit from the ecosystem services provided by these habitats in terms of currently unknown long-term carbon storage potential. The wider public in the UK has an appetite to see these natural coastal habitats protected and we are pleased to have developed a component of citizen science within the project to help engage a wider, non-academic audience.


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Description Evidence to Parliamentary Committee of Scotland's Climate Change Plan update (2021)
Geographic Reach National 
Policy Influence Type Gave evidence to a government review
Impact Focus on Blue Carbon and potential to contribute to Net Zero
Title Change in saltmarsh extent for six regions across Great Britain (1846-2016) 
Description Data are presented showing change in saltmarsh extent along 25 estuaries/embayments in six regions across Great Britain, between 1846 and 2016. Data were captured from maps and aerial photographs. Marsh extent was delineated a scale of 1:7,500 by placing vertices every 5 m along the marsh edge. Error introduced from: (i) inaccuracies in the basemap used to georeference maps and aerial photographs; (ii) the georeferencing procedure itself; (iii) the interpreter when placing vertices on the marsh edge; and (iv) map and photo distortions that occurred prior to digitisation were calculated and used to estimate the root mean square error (RMSE) in areal extent of each marsh complex. Measures of marsh extent were only recorded if maps and aerial photographs were available for the entire estuary/embayment. Data was collected as part of a study on the large-scale, long-term trends and causes of lateral saltmarsh change. The data was used in the analysis for Ladd et al. (2019). C. Ladd and M.F. Duggan-Edwards carried out the collection and processing of the saltmarsh extent data. All authors contributed to the interpretation of the data. The work was carried out under the NERC programme - Carbon Storage in Intertidal Environment (C-SIDE), NERC grant reference NE/R010846/1. 
Type Of Material Database/Collection of data 
Year Produced 2019 
Provided To Others? Yes  
Description Royal Society Summer Science Exhibition 2020 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Public/other audiences
Results and Impact C-SIDE project was selected to exhibit at the Royal Society Summer Science Exhibition 2020.
Year(s) Of Engagement Activity 2020