Podcast: Carbon capture and marine life

Industrial landscape

Carbon dioxide emissions from an industrial landscape

23 December 2014 by Sue Nelson

This week in the Planet Earth podcast, Jerry Blackford and Steve Widdicombe of the Plymouth Marine Laboratory (PML) talk about the world's first carbon capture and storage leakage experiment which looks at its effects on the marine environment.

To assist those who find text-based content more accessible than audio, a transcript of this recording is available below.

Sue Nelson: This time on the Planet Earth podcast - the successful completion of the world's first carbon capture and storage leak experiment. Hello, I'm Sue Nelson and I am by Plymouth Sound. There are some seagulls, yachts sailing in the bay, a lighthouse ahead and some building works behind me and two scientists from the nearby Plymouth Marine Laboratory were involved in the QICS project - quantifying and monitoring potential ecosystem impacts of geological carbon storage. They are lead scientist, Jerry Blackford, and benthic ecologist Professor Steve Widdicombe.

Now the aim of the project is to understand how the UK Marine Environment responds to potential leaks of carbon dioxide from the carbon capture and storage or CCS system. CCS is increasingly being seen as a potential technology in order to mitigate against the effect of climate change. Jerry, you didn't actually do your experiment here at Plymouth Sound but in Scotland - why?

Jerry Blackford: That's right, yes. We chose Scotland for a number of reasons, mainly because the scientific diving facility is located in Oban and we needed a lot of divers to do this experiment efficiently. The other reason is that the environment near Oban provides the perfect location for what we needed to do. We needed a relatively unpolluted environment but also quite sheltered with good access to the shoreline.

Sue Nelson: So what did you actually do?

Jerry Blackford: What we decided is that we were only going to make progress if we actually tried to replicate as near as possible what a leak might look like. We don't expect leakage to happen but we need to test what happens if it does. So we decided that we needed to actually inject CO2 below the seafloor and see how it moves through the sediment and then up into the water column, how we can best monitor that CO2 which is a regulatory need and also what kind of environmental impact it has. So we drilled a hole from land, 350 metres out underneath the bay. At the end of the pipe there was a long diffuser, that about 11 metres below the seabed, and we pumped CO2 through that for 37 days.

Sue Nelson: How did you measure then that carbon dioxide was leaking through the seafloor and up into the air?

Jerry Blackford: Well the first obvious thing that you see is bubbles coming from the seafloor which are fairly-

Sue Nelson: Like a carbonated drink?

Jerry Blackford: Exactly like a carbonated drink, exactly. But we also used a lot more sophisticated methods - we use seismic imagery of the sediments to see how far the gas was spreading, whether it was forming chimney, like focused float areas, whether it was defusing through and then we had lots of chemical sensors in the water column to look at the change in acidity that CO2 causes in seawater and we had cameras to look at impacts as well as taking samples of sediments and analysing in the lab later on.

Sue Nelson: And what was the percentage of carbon dioxide that was leaking.

Jerry Blackford: One of the big surprises for us... of the injected CO2 only about 15% made it across the seafloor and into the water column. We were quite surprised about that.

Sue Nelson: Pleasantly surprised?

Jerry Blackford: Just surprised because we must stress that we weren't testing storage, so we were trying to make the CO2 look like it was leaking. That was the aim of the experiment. But we were very surprised that the shallow sediments could hold on to so much CO2.

Sue Nelson: What effect did it have on the alkalinity of the water?

Jerry Blackford: It doesn't really affect the alkalinity of the water but it has a really interesting effect on the alkalinity of the sediments. What actually happens is that CO2 dissolves into the pool water and sediments, a little water in the space between the sand and mud particles and there is causes a process called dissolution and all the remnants of seashells, shells of animals, dissolve and it actually creates a buffering system. So the chemical effect in the sediment is actually greatly reduced. Now, again, that may be a relatively short term effect and we would like to test in the future how long that effect would last. But that is really why so much of the CO2 stayed around in the sediments and didn't come up into the water column. In the water column we did see a change in the acidity, as we know CO2 makes seawater more acidic and we measured that and that was quite clear.

Sue Nelson: In terms of marine life, Steve, did you see any positive or negative effects?

Steve Widdicombe: Well we certainly didn't see any positive effects, in particular the central zone where the CO2 was actively bubbling out and as Gerry has said the chemical effects were perhaps less than we thought they would be, but even so it was clear that there was a detrimental impact on the marine organisms that were actually living within the sediment itself. We've known for many years that exposure to high CO2 levels does effect organisms and particularly organisms that rely on calcium carbonate shells, such as the molluscs that live in the sediment and even the crustaceans as well, so we were able to see quite significant changes to the communities living within the area that was most effected by the leak.

Sue Nelson: Communities of what?

Steve Widdicombe: Crabs and worms, all the animals that would be burrowing deep within the sediment itself. They were exposed to these changes in chemistry within the sediment and therefore their physiology in their behaviour and their health was affected. But I think one of the most interesting things that came out of this study was the importance of understanding how these communities change naturally with time. Now we know that throughout the course of a year the communities change in response to the seasons. The supply of food, the changes in temperature and those signals are very, very strong. So in order to be able to detect the impacts of something like CO2 leakage it is very important to understand the influence of the leak in respect to the natural changes that are going on anyway. So in order to do that we not only looked at the communities in the area where the CO2 was actively leaking, but we also looked at reference sites and the key thing is to understand that we need good reference sites to any CCS activity to be able to understand whether change is natural or whether it is caused because of the activities of the CCS.

Sue Nelson: Often when there is any change in environment, you do get some winners and you do get some losers, were there any communities in marine life that, actually, it didn't have any effect?

Steve Widdicombe: Not that it didn't have any effect, there were organisms, particularly very small organisms like [unintelligible], like nematodes which did seem to increase in abundance in some areas. Now this isn't because they like high CO2 conditions but what it means is that they are actually being released from some of the ecological pressures that would normally keep their abundances in check. So, for example, if they are being pre-dated on by larger organism or being out competed for food the removal of these more CO2 sensitive organisms would actually free up a bit of resource for them. So, on the face of things it might look a good thing and a short term increase in their abundance might be seen but, again, in the long term we are not sure how sustainable that would be.

Sue Nelson: Jerry, the North Sea is seen as a potential very large scale area of storage for CCS technology, does the success of you project lead to... basically it must lead to a lot of good news for potential schemes in the future.

Jerry Blackford: Yes, I think it is a relatively positively message for CCS. It is the first time it has ever been done in the world and we've attracted a lot of interest from other countries. Not only do they want to see our results but are very keen to join in with our work. Whilst we saw an impact on the eco-system where we released to CO2, one of the most striking things was that the system recovered very quickly. So as soon as we stopped injecting CO2 the chemical changes disappeared within a couple of days and the biological systems actually recovered to pretty much what they were to start with or what they should be at that time of the year within about three weeks. So I think that is encouraging and it does show if there were a small leakage from a CCS system, it probably almost certainly wouldn't be an environmental catastrophe.

Sue Nelson: In a real case scenario would the carbon dioxide be injected and stored at a much deeper level?

Jerry Blackford: Absolutely. Most storage would be in rock strata between a kilometre and two kilometres below the seafloor, so there is an awful lot of rock for the CO2 to move through. And in fact if you consider natural gas that has been in the North Sea that we have been extracting for several decades now, that has been there for millennia and it stays there, it doesn't come up. So I think there are many reasons to think that if CCS is done properly with all the appropriate monitoring in place, with the appropriate choice of storage sites, the CO2 should stay there.

Sue Nelson: It's not often we have good news stories on the Planet Earth podcast, that just seems the nature of it, but this is a good news story in terms that it is has a successful outcome. Where do you go from here?

Steve Widdicombe: Well it was a very successful project and it has given us a huge amount... more understanding than we had before we started, but I would also offer a word of caution in the fact that this is the one time we have done it and we know the biological responses and environmental responses are incredibly dependent on the context in which they are done. You can get different outcomes based on what time of year you do things, in which habitats you do them, how much CO2 you're going to release, how long that release is for, so I think to generalise broad scale from just this one experiment I think would be unwise at the moment. We definitely need to understand how the different context under which leakage might occur would affect the results that we see, so really this is a great story. We have managed to demonstrate a way in which we can run these experiments in a way we've never have been able to before, but it really just opens the door to the fact that we need to be generating this kind of information over a much broader suite of habitats and communities and situations.

Sue Nelson: Jerry Blackford and Steve Widdicombe, thank you both very much indeed. That's the Planet Earth podcast from the Natural Environment Research Council and I will put up some pictures from today's recording on our Facebook page and Twitter feed. I am Sue Nelson from Plymouth Sound, thanks for listening.