Rain Determines Whether Peat Is A Carbon Sink Or Source

Even undisturbed peatlands might release rather than trap carbon dioxide, depending on seasonal rainfall patterns.

AsianScientist (July 18, 2017) – In a study published in Proceedings of the National Academy of Science, researchers have found that seasonal rainfall patterns can affect the release of carbon dioxide from tropical peatlands.

Peat, which is mostly organic carbon, forms when partially decomposed vegetation accumulates. Tropical peatlands can store gigatons of carbon in the form of peat domes, gently curved landforms than span several kilometers. However, climate change or changes in drainage networks can cause peat loss, leading to the release of the stored carbon dioxide.

In the present study, a team led by Dr. Alexander Cobb from the Singapore-MIT Alliance for Research and Technology have found that seasonal rainfall patterns play a crucial role in determining the shape of peat domes, which in turn affect whether peat is formed or lost.

Using geomorphological data from a pristine peat forest in Brunei Darussalam, Borneo, the researchers produced mathematical models that can predict the final shape of a tropical peatland based on the changes in rainfall patterns.

“Our work predicts that tropical peatlands gradually approach a shape in which the surface of the land, on the scale of kilometres, has a uniform curvature,” Cobb told Asian Scientist Magazine.

“We can also predict the curvature from the rainfall pattern. This means that we can predict how much peat, and therefore how much carbon, a particular landscape can hold.”

Dr. Alexander Cobb (third from left) and his team on site at Brunei. Credit: Alexander Cobb.

According to Cobb, even variation in the average time between storms can significantly change the amount of peat that a landscape can store.

“This finding was surprising, but makes sense, because a peatland sheds water far more rapidly when it is wet than when it is dry. This rapid shedding of water means that high rainfall during wetter times does not contribute as much to waterlogging and peat accumulation as compared to rainfall during drier times,” Cobb explained.

Additionally, the study shows that peat accumulation occurs at different rates within the peat domes: While peat first stops accumulating near rivers, accumulation continues further into the peatland. This means that the rates of carbon dioxide emission in peatlands are not the same across the landscape.

Nonetheless, Mother Nature isn’t the only one with influence over peat accumulation and carbon storage in the peatlands. Artificial drainages, too, are known to affect more than half of Southeast Asia’s peatlands, and there is an urgent need for a way to quantify such carbon emissions. Fortunately, Cobb believes that their models can help with the planning of drains to tackle carbon re-emission from tropical peatlands in the long term.

“Our models are useful for planning drains, and for predicting their effects because the principle of uniform curvature indicates how the shape of the peat surface must change in the long term,” he said.

“For example, if a peatland is cut by a series of parallel drains, we can predict the shape of the peat surface between the drains to be a low, mounded ridge. And after the drains are cut, our model predicts that the amount of peat will ultimately either decompose to release carbon dioxide, or burn to produce haze.”

Having made these mathematical models, Cobb and his team are now interested in knowing how differences in rainfall pattern, vegetation, and soil conditions may affect peatland development in other parts of the tropics, especially in Southeast Asia.

“We are now working on better understanding how nutrients used by trees in tropical peatlands, which will help us to better understand how hydrology and forests interact with each other to sequester or release carbon in tropical peatlands. This will help us to better understand how hydrology and forests interact with each other to sequester or release carbon in tropical peatlands,” said Cobb.

The article can be found at Cobb et al. (2017) How Temporal Patterns in Rainfall Determine the Geomorphology and Carbon Fluxes of Tropical Peatlands.


Copyright: Asian Scientist Magazine; Photo: Alexander Cobb/Singapore-MIT Alliance for Research and Technology.
Disclaimer: This article does not necessarily reflect the views of AsianScientist or its staff.

Anthony is a philosophy major at Nanyang Technological University and he reads Kant so that you don't have to. If he's not thinking about issues in the philosophy of science, language, or bioethics, he could be found reading, writing poetry or practicing parkour.

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