Underwater forests, the solution to ocean acidification

Did you know that there are underwater forests in the ocean? Maybe you felt it on your leg when you went swimming and thought “yuk!” This could have been seaweed that you felt. But these plants are very important to us because they are being used to combat climate change. Nowadays our climate is rapidly changing. One of the main causes of climate change is the increase of CO₂ in our atmosphere, due to the burning of fossil fuels. Around 30% of the CO₂ that is emitted is absorbed by the oceans. When this happens it causes the oceans to acidify with many negative consequences for us as humanity, but also the rest of the environment. Scientists from the university of California and the Radboud university studied whether underwater plants could be a solution for ocean acidification as they absorb CO₂. Is this in reality possible or does this solution have drawbacks?

The problem starts in the atmosphere

The continuing increase in CO₂, says professor doctor Appy Sluijs from the University Utrecht, is a big problem for humanity and scientists discuss many ways to tackle this problem. Scientists and governments are discussing possibilities to simply reduce the amount of CO₂, released by us, in our atmosphere. Ways to reduce the CO₂ concentration is the use of more solar energy, nuclear energy or to store CO₂ underground to keep it from entering the atmosphere. But these solutions all have some drawbacks like price and safety. Besides that, some solutions are very difficult to carry out.

The importance of the oceans

Luckily we have the oceans, reducing the CO₂ concentration in the atmosphere just for free. This is one of the most important features of the oceans. However, the oceans are very important for not only us as humanity, but also for animals and the rest of the environment. We need the oceans for biodiversity, regulation of the climate and the production of oxygen. Scientists believe that between 50% and 80% of the worlds oxygen is produced by the oceans. This oxygen is produced by plants and other oxygen producing organisms. Without them it would be very hard for us, and for animals, to breath.

Threat of CO₂ to the ocean

However, it seems a good thing that the oceans absorbs CO₂ and thereby decreases the CO₂ concentration in the atmosphere, nothing is less true. When the oceans are absorbing CO₂ it causes the water to become more acidic. In other words, the pH drops because CO₂ reacts with water and then forms HCO₃^– and H⁺ ions. When there are more H+ ions, than the pH gets lower. So when there is a lot of CO₂ in the oceans, then there are a lot of H+ ions. It works the same when you compare mineral water to lemon juice. You can say that lemon juice has way more H+ ions than mineral water, so lemon juice is more acidic. This acidity poses a threat to marine organisms, ecosystems and human societies that depend upon them. Recently scientists in America and the Netherlands have developed a possible solution to combat ocean acidification. This solution involves the use of underwater plants. But how?

How eelgrass forests help reduce the CO₂ concentration

Researchers are finding that kelp, eelgrass, and other sea vegetation can effectively absorb CO₂ and reduce acidity in the ocean. Marine ecologist George Waldbusser, from the university of Oregon, and his team sailed Netarts Bay, in the state of Oregon, to perform a study. They planted baby oysters around the bay to see how they would develop. The only oysters that thrived were those protected by beds of eelgrass, which seemed to take up enough CO₂ and give the oysters a chance to grow. “Basically nothing outside of those beds survived”, says Waldbusser. So this study proves that vegetation indeed can help reduce ocean acidification because there were no other factors that could influence the survival of the baby oysters.

Planting underwater seagrass forests

Another scientist, Professor Leon Lamers from the Radboud University, tries a different experiment. He tries to improve water with vegetation by planting vegetation. Together with the Rijkswaterstaat and The Fieldwork Company, Leon is experimenting by planting seagrass seeds in the spring so they can than grow during this time. If his study is successful he wants to give the Grevelingenmeer and het Veerse Meer, in The Netherlands, a healthy boost. The difference between lakes and the oceans is that lakes have sweet water and oceans have salt water. Also, lakes have most of the time stagnant water that doesn’t move.  So we were talking about ocean acidification and Leon performed his experiments in a lake? That’s right! However, lakes can also become more acidic by absorbing CO₂ which may harm animals that live in that environment. Now take a look at figure 1, with an example of seaweed, to see the idea of reducing the CO₂ concentration in the oceans by actively planting vegetation and letting them grow.

Figure 1: Preventing acidification by absorption of CO₂.   If seaweed grows by absorbing CO₂, it is very effective method to prevent ocean acidification. It works like the same principle as with plants on land. CO₂ is absorbed by the plants and is converted with the help of sunlight to biomass and oxygen is produced as a bi-product. The amount of CO₂ surrounding the plants is decreased in this way.

Not intervening with the forests

But is it as simple as just planting vegetation and just waiting for the acidity to decline? Robert Eagle, an assistant professor at UCLA’s Institute of the Environment and Sustainability in Los Angeles California, doesn’t think so. He found out that due to climate change and human activities, the amount of kelp and seagrass declines. This is especially true in California, where kelp forests have disappeared in some regions of the ocean due to more urchins caused by human activity. To successfully plant more kelp or other vegetation it’s important not to intervene with the growth of the plants after planting them.  If humans do intervene, due to direct intervention, like the example with the urchins, or influences due to climate change, we don’t give these plants a chance to grow and the solution to reduce ocean acidification will not work.

Conclusion

So there is still a lot more that scientists need to investigate about vegetation’s acidification-fighting capabilities. It’s still unknown, for instance, how many plants are needed to have any effect, how wide an area might benefit and whether they would only make a difference during the day, when there is sunlight that the plants need to grow, live and survive. Appy Sluijs also says it will be very difficult for this concept to apply, because you need to find a way to get all that dissolved CO₂ right to the plants. Because some parts of the ocean have more CO₂ dissolved than other part of the ocean. So to make this work for instance in the North sea, we need the help of biology and new techniques he says. Appy thinks the best way right now still would be to capture the excessive CO₂ that is being absorbed by the oceans. So maybe storing CO₂ in kelp, eelgrass, seagrass and other vegetation is still a farfetched idea, in the future this method can make a real difference as new techniques are being developed every day by scientists. Also don’t forget: the future is closer than you think!

Resources:

1. https://www.ipcc.ch/site/assets/uploads/2018/02/WGIIAR5-Chap30_FINAL.pdf
2. https://e360.yale.edu/features/kelp_seagrass_slow_ocean_acidification_netarts
3. https://deeply.thenewhumanitarian.org/oceans/articles/2018/04/20/fighting-ocean-acidification-with-underwater-forests
4. https://www.ioes.ucla.edu/project/the-bay-foundation/
5. https://www.bnnvara.nl/vroegevogels/artikelen/zeegraszaadjes-injecteren-in-de-bodem
6. Interview with: Professor Doctor Appy Sluijs
7. https://ngojwg.org/seaforest-e.html