Climate and water-table levels regulate peat accumulation rates across Europe

PLOS One | https://doi.org/10.1371/journal.pone.0327422 July 23, 2025 2 / 16 Abstract Background Peatlands are globally-important carbon sinks at risk of degradation from climate change and direct human impacts, including drainage and burning. Peat accumulates when there is a positive mass balance between plant productivity inputs and litter/ peat decomposition losses. However, the factors influencing the rate of peat accumu- lation over time are still poorly understood. Methodology/Principal Findings We examine apparent peat accumulation rates (aPAR) during the last two millennia from 28 well-dated, intact European peatlands and find a range of between 0.005 and 0.448 cm yr-1 (mean = 0.118 cm yr-1). Our work provides important context for the com- monplace assertion that European peatlands accumulate at ~0.1 cm per year. The highest aPAR values are found in the Scandinavian and Baltic regions, in contrast to Britain, Ireland, and Continental Europe. We find that summer temperature is a signif- icant climatic control on aPAR across our European sites. Furthermore, a significant relationship is observed between aPAR and water-table depth (reconstructed from testate-amoeba subfossils), suggesting that higher aPAR levels are often associated with wetter conditions. We also note that the highest values of aPAR are found when the water table is within 5–10 cm of the peatland surface. aPAR is generally low when water table depths are < 0 cm (standing water) or > 25 cm, which may relate to a decrease in plant productivity and increased decomposition losses, respectively.

Model fitting indicates that the optimal water table depth (WTD) for maximum aPAR is ~10 cm. Conclusions/Significance Our study suggests that, in some European peatlands, higher summer temperatures may enhance growth rates, but only if a sufficiently high water table is maintained. In addition, our findings corroborate contemporary observational and experimental studies that have suggested an average water-table depth of ~10 cm is optimal to enable rapid peat growth and therefore carbon sequestration in the long term. This has important implications for peatland restoration and rewetting strategies, in global efforts to mitigate climate change. Introduction Peatlands comprise only ~3% of the global landmass but are globally important habitats, carbon (C) stores and valuable archives of past environmental and climatic change [1–3]. European peatlands contain approximately half of the continent’s total soil organic carbon, and five times more carbon than its forests [4,5]. Peatlands and reproduction in any medium, provided the original author and source are credited. Data availability statement: All relevant data are within the manuscript and its Supporting Information files. Funding: We acknowledge all the organiza- tions that have funded the data used in this analysis: Academy of Finland; Department for Employment and Learning (Northern Ireland); European Commission (Fifth Framework); INTERACT (European Community’s Seventh Framework Programme); Irish Discovery Programme; Leverhulme Trust; National Science Centre (Poland); Natural Environment

Research Council (UK); Natural Sciences and Engineering Research Council of Canada; Netherlands Organization for Scientific Research; Polish National Science Centre (2021/41/B/ST10/00060 and 2021/03/Y/ ST10/00093 [BIODIVRESTORE]); Quaternary Research Association; Swiss Contribution to the enlarged European Union; Swiss Federal Office for Education and Science; Swiss National Science Foundation; World University Network; Wüthrich Fund (University of Neuchâtel); and Yorkshire Water. T.G.S. was funded by the Leeds–York Natural Environment Research Council (NERC) Doctoral Training Partnership (grant no. NE/L002574/1). T.E.T. acknowledges NERC Doctoral Training Grant no. NE/G52398X/1. JMGs contribution rep- resents NRCan contribution number/Numéro de contribution de RNCan: 20230392. This paper is a contribution to the PAGES C-PEAT group. PAGES is supported by the Swiss Academy of Sciences and Future Earth. This research was supported by a grant to G.T.S from the UK Leverhulme Trust (Grant No. RPG-2021-354) and a grant to E.M.K from UKRI NERC (Grant No. UKRI182). Competing interests: The authors have declared that no competing interests exist.