Mongabay (30/12/2025) - The water-filled ditches that laced through the oil palm plantation in Sarawak, a Malaysian state on the island of Borneo, nagged at Kuno Kasak when he saw them in 2022. He knew that these canals, used to draw water out of spongy peatlands to make them suitable for agriculture, had been shown to be sources of methane. But just how much remains an open question, with too few data points to make estimates with certainty.

Though methane dissipates more quickly in the atmosphere than CO₂, it’s more than 20 times more effective at trapping heat. It’s also responsible for nearly a third of the global temperature rise since the industrial revolution, making accurate methane accounting imperative for addressing climate change.

Kasak, a professor of environmental technology at Estonia’s University of Tartu, is the lead author of a recent study in which he and his colleagues report that methane from these drainage canals accounted for as much as 10% of the total greenhouse gases from a given hectare of the oil palm plantations they studied. At the same time, the ditches covered no more than 4% of the plantations’ total area.

“This is significant because it means that previous estimates of emissions from drained peatlands likely underestimate the contribution from ditches, which are often ignored in global carbon accounting,” Kasak told Mongabay in an email. They also found that the ditches were sources of CO₂.

The team’s findings, published in the journal Scientific Reports Oct. 23, point to the need for more research to better understand the balance of emissions and, more broadly, the environmental cost of draining peatlands.

“Earlier studies often focused on soil or forest emissions and assumed that ditches were minor contributors, so they were not prioritized,” he added.

Peat is made up of dense mats of organic material that build up over centuries and millennia. Microbes would ordinarily start feasting on this plant matter and producing byproducts like CO₂. But when those mats are submerged in water, it chokes off the oxygen, slowing the decomposition and locking away carbon in the process. Globally, peatlands hold around 30% of terrestrial carbon — about twice what’s found in forests — on just 3% of Earth’s land.

The dynamics are complex, as the oxygen-poor environment of intact peatlands means that methane does seep from them as microscopic organisms adapted to living without oxygen break down the built-up organic material. Other research has posited that oil palm plantations don’t release as much methane as intact peatlands. But the work of Kasak and other scientists has shown that drainage ditches are an often-overlooked environment in which balmy temperatures, little oxygen and a bunch of dead plant matter also lead to the production of methane.

“Effectively, you’ve moved your methane emission from the peat into the canal network,” said Chris Evans, a peatland biogeochemist at the U.K. Centre for Ecology and Hydrology, in an interview.

Meanwhile, the once-swampy peatlands start to emit CO₂ as they dry out, adding to the overall carbon emissions released.

A decade ago, Evans, who wasn’t involved in the Kasak-led study, took part in early research aimed at quantifying greenhouse gas emissions from the ditches used to drain peatlands for agriculture. The small amount of data they were working with pointed to the ditches being a significant source of greenhouse gases. “They were big numbers, but obviously with huge uncertainties,” Evans told Mongabay. “That was what we had.”

Calculating emissions

The movement, or “flux,” of carbon into and out of peatlands is complicated and difficult to measure, in part because the relative release and uptake of carbon depends on factors like temperature, water chemistry and how much organic material is available.

Kasak and his colleagues measured the concentrations of CO₂, methane and nitrous oxide, another greenhouse gas, at several spots in two peatland oil palm plantations in Sarawak. One had been drained and planted originally in 2002, and the second in 2018. The team also used drone photographs to quantify the area covered by water.

The researchers looked at two types of methane emissions from the ditches. Until now, most research hasn’t teased apart the unique impacts of the steady “diffusive” flux of methane compared to the punctuated bubbling up of emissions known as “ebullitive” flux, Kasak said.

(Evans recalled seeing the bubbles rising behind his boat in a canal on an oil palm plantation: “You can literally see the water fizzing behind you. It looks like Coca-Cola.”)

The continuous diffusion of methane into the atmosphere is more predictable, Kasak said. Ebullitive flux, on the other hand, “occurs in sudden bursts, which makes it highly variable over time and difficult to model,” he added. That could lead to “substantial underestimates of [methane] emissions.”

“By measuring both separately, we can provide more accurate emission factors and reduce uncertainty when scaling from the ditch to the landscape level,” Kasak said.

The researchers were also surprised to find that methane emissions weren’t markedly lower in the older plantation, even though there was likely less organic matter available for methane-producing microbes to break down compared to the younger plantation.

Evans called the Kasak-led study “a useful piece of work” that backs up the hypotheses about emissions from ditches that had begun to percolate in the 2010s.

“It’s great to see people have been out there since then, actually filling that evidence gap,” he added.

The steps for reducing these emissions are “not obvious,” Evans said, though he suggested that the use of too much fertilizer could contribute to the problem. Still, once peatlands are drained, the release of greenhouse gases from them would be difficult to stop, he added. “It will happen if you put in a drainage network, unavoidably.”

Kasak, too, described mitigation as “challenging.” He noted that potential solutions could include adjusting water levels and limiting the amount of organic material that ends up in the ditches. But that would have to be balanced with farmers’ need to keep their crops productive.

He emphasized the need for robust data and more of it, adding that future studies should go beyond the “snapshots” provided by short-term monitoring to understand changes across seasons and conditions.

Ultimately, Kasak said, “These findings emphasize that ditches are a persistent source of greenhouse gases that must be accounted for in carbon budgets and climate models.”

Read more at https://news.mongabay.com/2025/12/ditches-on-peatland-oil-palm-plantations-are-an-overlooked-source-of-methane-study/