Blue Carbon and Green Kelp: Kelp forests could reduce carbon emissions

Citation: Filbee-Dexter, K., Wernberg, T. Substantial blue carbon in overlooked Australian kelp forests. Sci Rep 1012341 (2020).

Blue Carbon: What is it?

You’re probably familiar with carbon in all different forms, from pencils to diamonds, but have you heard of blue carbon? Blue carbon refers to carbon stored in marine ecosystems and is what many environmental managers and climate change experts are beginning to use to offset carbon emissions. Global climate change is continuing to occur and result in many environmental changes, many of which are undesirable for humans. Since carbon emissions are the leading cause of climate change, it is very important to identify carbon sinks, or natural storage areas, so that we can ensure carbon is being stored or sequestered rather than emitted. Scientists have set goals for carbon emission reductions in order to prevent further harm from climate change, and identifying and protecting possible carbon sinks is helpful to ensure that we can reach these goals efficiently.

How do Ecosystems Store and Sequester Carbon?

Recently, scientists have learned that vegetated coastal ecosystems, such as tidal marshes, mangrove forests, and seagrass beds, are very good at sequestering carbon. In fact, these ecosystems are even used in calculations to determine global carbon budgets to measure our success in reducing carbon emissions enough to reduce climate change. Vegetated ecosystems are good at sequestering carbon because the vegetation within them pulls carbon dioxide from the atmosphere during photosynthesis, resulting in carbon storage in aboveground biomass, and when the vegetation dies, the carbon becomes buried in the soil. Essentially, the carbon dioxide that was once in the atmosphere is now stored in the ground. Ecosystems that are very productive, or have high vegetation growth rates, ultimately store more carbon. Historically, tidal marshes, mangrove forests, and seagrass beds have been the only ecosystems containing blue carbon used in global carbon budgets. Kelp forests are another marine ecosystem that have very large amounts of aboveground biomass, and therefore could be considered a carbon sink.

The image on the left (source: Wiki Commons) shows the process of carbon storage and sequestration within a marine ecosystem, while the image on the right (source: Wiki Commons) shows the same for a forest.

How can Kelp Forests Help?

Aside from storing carbon in aboveground biomass, kelp forests also export detritus (organic matter produced when the kelp begins to decompose) to other marine ecosystems where it is then buried, resulting in carbon storage underground. In fact, about 80% of the production of kelp forests (about 153 Tg of carbon per year)  is exported to deep coastal areas, the continental shelf and slop, and the deep sea. One Tg is equivalent to one trillion grams. Two researchers from the Institute of Marine Research in Norway wanted to explore the contributions that kelp forests have to blue carbon. To do this, they chose to study Australia’s Great Southern Reef, which is dominated by kelp forests. They assessed the contributions of these kelp forests to blue carbon using areal extent of the kelp forests, total biomass, and productivity measures.

The image above (source: Flickr) shows a kelp forest similar to what the researchers would have studied.

The researchers found that Australia’s kelp forests contribute to greater than 30% of total blue carbon sequestered by marshes, mangroves, and seagrass beds, and about 3% of total global blue carbon. The aboveground biomass of the kelp forests in their study site store 11-23 Tg of carbon and contribute to 1.3-2.8 Tg of carbon sequestered each year. This is equivalent to 11-13% of total blue carbon and about 30% of annual carbon sequestration for the continent of Australia. Comparatively, the aboveground biomass of Australia’s kelp forests is very similar to that of its seagrass beds. The sequestration rate of Australia’s kelp forests is also similar to that of its seagrass beds and tidal marshes, but lower than that of mangroves. These results show that kelp forests have the potential to be good carbon sinks and help us to store carbon that would otherwise be released into the atmosphere.

While the results of this study are promising, the researchers brought up a few potential problems. First, because they did not include all of the kelp forests within Australia, their calculations may actually be an underestimate of the potential contribution of kelp forests to blue carbon. Another challenge is that since a lot of detritus from kelp forests ends up being buried in other marine ecosystems, the carbon storage potential of kelp forests may be accounted for twice when global carbon budgets are calculated. This would result in an inaccurate picture of how much carbon we are currently storing: we would think that we are storing more than we are. To overcome this challenge, the researchers used a lower productivity rate for the kelp forests to help compensate for potentially double counting kelp carbon. However, since the proportion of kelp productivity that ultimately ends up stored in other marine ecosystems is rudimentary, there is a knowledge gap and potential inaccuracies in their calculations. Either way, the potential contribution of kelp forests to blue carbon should not be overlooked. Since these forests appear to have as much potential for contributing to blue carbon as other marine ecosystems, we should also focus on their conservation and restoration to help reduce carbon dioxide emissions in ways such as the Blue Carbon Initiative is doing for other marine ecosystems. If we can increase blue carbon storage and reduce emissions, then we may be able to reduce the impacts of climate change, ultimately making life on planet Earth better for all.

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Elisabeth Lang

I recently graduated from Johns Hopkins University with a Masters degree in Environmental Science and Policy. My undergraduate education was at McDaniel College, where I majored in Environmental Studies and Biology. My undergraduate research focused on land use change and its impacts on biodiversity in Central America using GIS-based research. My graduate research examined potential sea level rise impacts on National Wildlife Refuges in the Mid-Atlantic region using GIS. I am currently working at the US Army Public Health Center where I analyze environmental samples. In my spare time, I enjoy traveling, reading, and running.

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