Freshwater sediments may play a bigger role in slowing methane emissions than previously thought

Methane is one of the most powerful greenhouse gases in Earth’s atmosphere, and wetlands together with inland waters are among its largest natural sources. But in the freshwater sediments, specialized microorganisms consume part of this methane before it can escape into the air.

A new study sheds light on the environmental controls governing this natural methane consumption. The study was published in Limnology and Oceanography and is available here: https://aslopubs.onlinelibrary.wiley.com/doi/pdfdirect/10.1002/lno.70373

The study was performed in the group of Bo Thamdrup, who is a Professor of geomicrobiology at the Department of Biology, University of Southern Denmark (SDU). The experimental efforts were led by postdoc Alina Mostovaya and PhD student Michael Wind-Hansen, who are now both at Aarhus University but were at SDU when the work was conducted.

The researchers investigated sediments from Lake Ørn in Denmark and managed to quantify, for the first time, how the availability of sulfate and iron controls anaerobic oxidation of methane in freshwater sediments.

Their findings provide new insight into the microbial processes that regulate methane emissions from lakes, wetlands, and other aquatic environments.

Freshwater environments like lakes are often considered important natural contributors to climate change, because methane is released from the water surface. Often, one can see the methane leave the water as bubbles that burst once they reach the surface, releasing methane directly into the air.

But according to the researchers, a considerable amount of methane could very well be consumed in the sediment.

“If this mechanism was not at play, more methane would leave the lakes”, says corresponding author Alina Mostovaya. 

The researchers describe the mechanism as an underappreciated methane sink that should be considered when making models for balancing production and consumption of methane in freshwater environments.

The driver of the investigated methane consumption in the studied Lake Ørn is microbial activity. Certain microbes use sulfate and iron in the sediment to consume methane under oxygen-free conditions.

Neither sulfate nor iron are rare elements in freshwater sediments. Sulfate may, for example, enter with rain and runoff from soils, nearby fertilized fields, wastewater or seawater intrusion. Iron is one of the most abundant elements on Earth and may come from weathering of rocks and soil or is carried by rivers and groundwater. 

The methane-consuming microbes at play belong to the archaeal group ‘Candidatus Methanoperedenaceae’, and they appear to be quite efficient even in low-resource freshwater environments:

“Our work in Lake Ørn shows that even relatively low concentrations of sulfate can support efficient methane removal in freshwater sediments,” says co-author Michael Wind-Hansen.

The researchers found that sulfate-dependent methane oxidation in Lake Ørn operates efficiently at sulfate concentrations in the low micromolar range — far lower than typical values reported from marine systems. This suggests freshwater microbial communities have evolved high-affinity strategies for scavenging scarce resources.

The team also showed that iron-dependent methane oxidation requires relatively high concentrations of reactive iron minerals, but nevertheless represents an important pathway for methane removal in the lake.

Their experiments further revealed that dissolved organic compounds resembling natural humic substances can shuttle electrons between microbes and iron minerals, significantly stimulating methane oxidation under certain conditions.

“These electron-shuttling compounds may help microorganisms take advantage of iron minerals that would otherwise be difficult to use,” Alina Mostovaya says, “That means natural organic matter may play a dual role in many freshwater environments, both as a source of methane and as a regulator of methane consumption and emissions.”

The findings have broader implications beyond a single Danish lake.

“We expect that the same pattern can be found in many other lakes and freshwater environments in other parts of the world, so this is a factor that should be considered when making global models of methane production, consumption, and emissions in these environments”, says Professor Bo Thamdrup.

Journal Limnology and Oceanography, April 23, 2026: Kinetics of sulfate- and iron-dependent anaerobic methane oxidation in freshwater lake sediment. doi: 10.1002/lno.70373. Authors: Alina Mostovaya, Michael Wind-Hansen, Bo Thamdrup.

The study was financed by the European Research Council (project NOVAMOX) and the Independent Research Fund Denmark.