How do climate and groundwater levels regulate the rate of peat accumulation?

Peatlands occupy only 3 percent of land area, but they are of great ecological and climatic importance. In Europe, they store half of the total organic carbon present in the soil – 5 times more than continental forests. An international team of scientists, with the participation of Prof. Mariusz Lamentowicz of Adam Mickiewicz University in Poznan, decided to study the rate of peat accumulation in Europe.

Resilient but vulnerable to change

A key function of peatlands is their ability to accumulate peat, and thus store carbon for the long term. This process occurs when the amount of organic matter supplied by plants exceeds the losses caused by decomposition.

Natural peatlands are ecosystems that depend on high groundwater levels, which slow down the decomposition of matter by microorganisms and promote an increase in their thickness. Peatlands dominated by peat mosses(Sphagnum) are the fastest growing. Unfortunately, the functioning of most European peatlands has been disrupted by human activities: land reclamation, agriculture, peat extraction, burning, afforestation and pollution. Also, climate change can exacerbate negative processes by lowering water levels and increasing the rate of decomposition of matter.

What do we learn from the story?

To better understand how peatlands are responding to climate change, researchers analyzed paleoclimatic data from 28 intact peatlands across Europe. The study, the results of which were published in the July 22 issue of the journal PLOS ONE, included historical data from the past 2,000 years. Accurate peat sediment dating models were used for the analysis, while the apparent peat accumulation rate(aPAR), expressed in centimeters per year, was used as a key indicator.

How fast are bogs growing?

The rate of peat accumulation varied from 0.005 to 0.448 cm/year at the surveyed locations. The average rate between locations was 0.118 cm/year, and the average of all measurements was 0.140 cm/year. The highest values were found in the peatlands of Scandinavia and the Baltics.

The analysis showed that higher summer temperatures (June-August) are associated with an increased rate of peat accumulation. Both modern and paleoclimatic data confirmed this relationship. In the case of the historical data, the Theil-Sen regression coefficient for mean aPAR was 0.52, and for maximum aPAR was 0.55. These correlations were statistically significant.

Other climatic variables, such as precipitation or the number of growing degree days (GDD), did not show such clear correlations with peat growth. However, some non-linearity was detected – too much precipitation can limit the growth of peat-forming plants due to an increase in the area of open water.

The key factor regulating peat growth, in addition to temperature, is the depth of the groundwater table (WTD). The highest rate of accumulation was recorded at a water table located 5-10 cm below the peat surface. At WTD deeper than 11 cm, high aPAR values were not found. Statistical models indicate that the optimal water level is about 10 cm – exactly the level recommended in studies of WTD and effective peatland restoration.

Peatlands as self-regulating systems

Although peatlands can independently transition from erosion to carbon re-accumulation, the study highlights their sensitivity to exceeding certain environmental thresholds. For example, lowering the WTD below 25 cm increases microbial activity and intensifies peat decomposition. In turn, water levels that are too high can lead to reduced plant productivity.

Researchers emphasize that effective peatland restoration should take into account optimal groundwater levels. Simple irrigation without considering the peculiarities of the local ecosystem can do more harm than good – in the form of methane emissions, for example. Paleoecological data indicate that peatlands naturally strive to maintain water levels conducive to their growth – about 10 cm. This is a value that can be taken as a benchmark for conservation and adaptation measures.

Peatlands are not only archives of environmental change, but also our active allies in the fight against global warming. Their ability to store carbon depends on the subtle connections between temperature, precipitation and groundwater levels. A study spanning thousands of years of the history of Europe’s peatlands indicates that effective protection and restoration of these ecosystems requires a precise approach, based on data and knowledge of how they function.

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MAIN PHOTO: Jordi Escuer/Flickr

Source:

Swindles GT, Mullan DJ, Brannigan NT, Fewster RE, Sim TG, Gallego-Sala A, et al. (2025) Climate and water-table levels regulate peat accumulation rates across Europe. PLoS One 20(7): e0327422. https://doi.org/10.1371/journal.pone.0327422