Carbon Storage in Intertidal Environments (C-SIDE)

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.