Adding water to mires doesn’t always boost carbon uptake

- These results challenge the prevailing scientific paradigm that more water automatically leads to greater carbon storage in mires. Our study shows that multiple factors must be considered to fully understand how mires sequester carbon, says Betty Ehnvall, SLU researcher and lead author of the study recently published in Nature Communications.

A mire is a type of wetland where oxygen-poor water slows down the decomposition of dead plant matter, resulting in peat formation. This process allows mires to store carbon that would otherwise be released into the atmosphere, contributing to climate change. Until now, it has been generally understood that wetter mires are better at capturing carbon. But the mires examined in this study tell a different story.

- We investigated eight mires in the coastal region of Västerbotten in the north of Sweden. Younger mires with higher inflow of water decompose plant material more rapidly than older mires in the area, and therefore store less carbon. This appears to be linked to the water’s chemical composition, says Ehnvall.

The groundwater flowing through these mires has been in contact with mineral soil, which has enriched the water with minerals. This mineral enriched water reduces the mire’s capacity to store carbon.

- Peat formation is a complex process and its extent is controlled by a number of environmental factors, says Mats Öquist, researcher at the Department of Forest Ecology and Management, SLU, where the study was conducted.

It is only when we understand these interactions that we can effectively predict and optimize the climate impact of peatlands.

- This research shows that wetland rewetting must take into account the entire hydrology of the landscape - not just keeping the soil wet, says Kevin Bishop, Professor at the Department of Water and Environment, SLU.