Humans can feel that we have built a world to live in that is above and apart from nature. We concrete the ground, we regulate the temperature of our spaces, and we shield ourselves from storms. But increasingly wild and frequent weather events are making us doubt the endurance of our fortress of glass, steel, and stone.
Faced with the environmental triple threat of carbon emissions, biodiversity loss and flooding, engineers and scientists are increasingly looking to nature for solutions. And that is what a group of experts have done at a marshy stretch of land on the Firth of Forth.
The Firth is the estuary of the Forth River, which passes by Edinburgh. It has for centuries been a strategic seaway, linking the heart of Scotland with the rest of the world. It has low-lying fertile land and also dramatic escarpments. It is a fjord, carved out by the Forth Glacier during the last glacial period, but the most significant changes since the retreat of the ice sheets have been human. The coming of industry and the expansion of agriculture led to the construction of sea walls to hold back the tides and reclaim land for exploitation.
Remaking the banks of the Firth of Forth
It is also the site of a project that could change the way we think about the management of our coastline. Because in the grey of morning on Wednesday 3rd October 2018, an excavator fired into life at a location on the southern bank of the Firth. After years of discussion and months of planning, teams working at the direction of the RSPB – the Royal Society for the Protection of Birds – breached the sea wall and allowed the tide to flow through.
The site is called Skinflats RSPB Reserve and is part of a managed realignment of the existing coastline to allow tidal waters to once again inundate an area of land. Land that was previously ‘reclaimed’ from the waters.
The new intertidal habitat is an ecological environment called a saltmarsh. A marsh that sits between dry land and open saltwater, and floods each high tide. Salt tolerant grasses and shrubs trap and bind sediments… that part will be important later.
Like the more famous mangrove forests of the tropics, a saltmarsh is a natural flood barrier and a highly biodiverse ecosystem.
These are both good things. The saline lagoons and marsh are already attracting birds back to the area. But while this is all going on, there has been a flurry of excitement at the nearby University of St Andrews. The Skinflats reserve is exactly the type of environment they have been studying for some time.
Increasing academic interest
Professor Bill Austin is a marine geoscientist in the university’s School of Geography. He also works at the Scottish Oceans Institute, so is broadly involved in the marine sciences, but also looking at coastal processes. He has worked to tie modern measurements of the climate with what we can learn from paleo climate records in the natural world – sediment records for example.
“And then over the years, we realised that these sediment records that we were working on hold vast amounts of stored carbon,” says Austin. This realisation that there was sedimentary carbon in the marine environment, and that it could and should potentially be considered as a carbon sink (and store) led to the concept of ‘Blue Carbon’.
“Blue carbon can be defined in the strict sense in the way that the Intergovernmental Panel on Climate Change, the IPCC would define blue carbon as coastal vegetated ecosystems. So the three main habitats we would recognise would be mangrove forests, salt marsh, and seagrass meadows.”
The sedimentary process in coastal environments derives its carbon from two sources: terrestrial sources (meaning from river systems) and marine sources.
“Now, in both these cases, the carbon is originally fixed through photosynthesis, from carbon dioxide in the atmosphere. So it’s a nature based approach whereby plants and other organisms are taking in carbon that would otherwise be in the atmosphere, and they lock it away in organic matter, and some of that organic matter becomes stored in the sediments.”
Although the firth may have been formed as a fjord, the fjords on the west coast of Scotland have a more traditional look to them – much narrower and sharper. And the University has studied them extensively. They are natural sediment traps, much like the U-bend in a sink.
“They’re very good at capturing sediments, and therefore storing carbon. And the first reason we went to study these systems was because we thought they would have very rapid sediment accumulation and burial. And this would give us very expanded detailed climate records. That was where we started, then we realised they were also very effective burying carbon. So we actually called these systems, global carbon hotspots. They are recognised globally, as very important places in the Earth system that stores carbon.”
The importance of stores
Carbon storage is very much on people’s minds at the moment, and due to COP26 there has been a deal of interest in the potential of these carbon sinks. Work is ongoing to quantify the net carbon capture effect of these places, but it is thought that Scottish sea lochs (or fjords) lock away 3 to 4 times the annual emissions of Scotland.
“So that gives you some sense of the magnitude of the store that’s building up in these natural systems. And in fact, one of the things that we’re really focused on as we disturb the marine environment more and more all sorts of activities, and, you know, is the idea that we might disturb the carbon in the sediments, and therefore, a move towards understanding the stock of carbon in these sedimentary systems and the need to avoid emissions through that disturbance process.”
Into this field of study came the Skinflats RSPB reserve.
“I think quite an exciting one, when we think about the context of sea level rise, we can hold the line, as many engineering solutions for coastal infrastructure need to and hold the sea back. But increasingly, we’re recognising that we can let the sea back in to some places where it’s appropriate to do that. And these habitats are naturally forming in our coastal environments, they’re intertidal. And they form very quickly, typically within one to three years, we would see the natural system re-establishing itself.”
And quite quickly, those ecosystems start to function deliver all sorts of benefits for nature, biodiversity… but also start to build up new stores of blue carbon. So for Bill and his department this is quite an exciting, emerging opportunity.
“It’s probably not appropriate everywhere. But where we can do this, I think there are fantastic opportunities. And we also need to recognise in England, for example, it’s estimated historically that somewhere between 80 and 85%, of our coastal salt marsh habitats were reclaimed. You know, in recent centuries, we did this for agriculture and other sorts of opportunities. But these are places particularly with sea level rise that we could reimagine and let the sea back in. And this does create all sorts of opportunities.”
A major ongoing project at the moment is a national inventory of carbon stock and Bill has been leading a project to estimate the amount of carbon that is stored in these coastal wetlands.
“These coastal managed realignment schemes are increasingly important in terms of upset flood management, but they offer an opportunity to think about the additional carbon and there’s an investment opportunity in those carbon credits that individual corporations might want to purchase as part of their emissions management. Their offsetting if you like.”
Ultimately, some activities and industries will be very difficult, if not impossible to decarbonise.
“So this creates a very interesting opportunity, a synergy if you like, where if we develop this science To demonstrate the additional blue carbon benefits, we could help with some of these schemes in terms of private investments, you know, that would perhaps help push your scheme over the line.”
One of the challenges is to think about land management, ownership and the current planning system Austin puts it more simply: “the cost of buying farmland, to then flood it is not insignificant.”
So it requires thinking carefully about a variety of stakeholders.
“And, of course, I think for the public, they would naturally have this idea that we hold back the sea to create coastal flood protection. And we need to change some of the thinking around the benefits of managed realignment, often these are large engineering projects. And I think we need to work with a whole range of partners to convince everybody that, you know, in the right place, these are very good schemes.”
Austin’s work at Skinflats has primarily focused on the natural salt marsh adjacent to the actual coastal realignment site. The potential for carbon storage, and also the rate of carbon accumulation in the sediments.
“We’ve used radio nuclide traces, so lead to 10 caesium fallouts create spikes in our stratigraphic record. We’ve used this to date, the accumulation of those sediments at that site. And what we find is that skin flags in the fourth estuary, close to Edinburgh, actually has very high sediment and carbon accumulation rates.”
They think this is driven by the high sediment load that comes down through the forth.
“It’s quite turbid muddy water. And the plants act as natural baffles. And they trap the sediment, and they build up over time. So this is how a marsh system would accrete. And actually, with sea level rise, these marshes, if they have sediment supply, will keep building up and will accumulate and accumulate carbon as sea level rises. We think the fourth is actually a very good place for these schemes. We probably didn’t know that until quite recently. But it does turn out to be a good place for this type of managed realignment scheme.”
Analysing the best sites is important, to make the most of finite resources for reworking the coastline. To do this analysis they are looking at projections of future sea level rise, which uses numerical models to input different atmospheric greenhouse gas concentrations and so calculate the rise.
This is then compared to digital elevation models and high-resolution LIDAR data to project the impact of these projected sea levels on the land.
Then historical maps are consulted to sea which of these areas correspond with former salt marshes. And that allows the researchers to quickly identify the best places for managed realignment projects.
“And this has been done actually by the RSPB for the entire United Kingdom, but not using the sea level projections. And there are literally thousands of hectares potentially available for these schemes. So we could then think about the other criteria, as I’ve mentioned, perhaps sediments supply that would allow these systems to build up over time, perhaps the value of the adjacent land, you know, so we could think about the most cost effective place. And then also other considerations like the need for flood protection, flood, defence, and so on and so forth. So I think there are ways to do this.”
Natural savings
The economics of this are yet to be fully worked out, but with a renewed government focus on solutions to the climate emergency, more work to understand this is expected. There is also work needed to understand the net effect of managing these sites on the carbon cycle.
“If we could get the habitat into the national greenhouse gas inventory, I think this would be a further incentive for the government, because there would be some benefits to as towards our Net Zero ambition. And I think the other benefits are going to come from private investors. We shouldn’t expect government to fund all of these schemes, and private investors who are looking for carbon credits. And these schemes are quite attractive.”
Blue carbon is an evolving field of study, and it also incorporates sinks in the open seas, not just along the coastline. Scottish waters are five times the size of the land area.
“And we placed a great deal of emphasis on our forests and our peatlands here in Scotland as part of the solution to reducing greenhouse gas emissions. We haven’t really put that emphasis on our seas yet. And I think we don’t fully understand the magnitude of the sink.
“But we know it is at least an order of magnitude greater than the terrestrial soil store. So if we are worried about avoiding emissions, I would argue that protecting some areas of our seabed to avoid emissions, could be a really useful strategy. But I have to admit that we don’t have all the evidence that we need to really inform a policy in this area yet, but we’re moving in that direction. It’s quite exciting times.”
So what can we say about the global potential for Blue Carbon, what is that headline number?
“That’s quite a challenging question. We’re getting close. I think, what I would say is that, broadly, it’s been estimated that globally, Blue Carbon can offer about one to 3% of what we need to achieve global warming and keep it within the 1.5 degrees. scenario that was agreed at Paris. Doesn’t sound very much, but it does accrue year on year. If we have these healthy systems, they’re also storing that carbon.
“And those stores build up over time. As we get closer and closer to the net zero to Get, we’re going to have some hard to remove emissions, you know, agriculture is always going to give us some emissions, particularly red meat production, ruminants. And so these natural savings become quite important in that balancing act.
As with so many of these solutions, it is one tool of many to mitigate the challenges ahead of us.
