HGS RESEARCH HIGHLIGHT – External and internal drivers behind the formation, vegetation succession, and carbon balance of a subarctic fen margin
Juselius-Rajamäki, T., Piilo, S., Salminen-Paatero, S., Tuomaala, E., Virtanen, T., Korhola, A., Autio, A., Marttila, H., Ala-Aho, P., Lohila, A., & Väliranta, M. (2025). External and internal drivers behind the formation, vegetation succession, and carbon balance of a subarctic fen margin. Biogeosciences, 22(12), 3047–3071. https://doi.org/10.5194/bg-22-3047-2025
“The model allows explicit simulation of water exchange between groundwater and surface water and can be parameterized using physical properties of peat and mineral soils. The high spatial resolution of the model makes it suitable to estimate water fluxes at the scale of vegetation inventories and remote-sensing data. ”
Figure 7. (a) The GW–SW exchange flux patterns from the Lompolojänkkä sub-basin averaged for summer 2017, representing the current climate conditions. Positive flux values indicate the locations of groundwater exfiltration and infiltration towards groundwater. (b) The groundwater table elevation changes result from the drier climate conditions. Negative values indicate that the groundwater level decreases, whereas and positive values indicate that the groundwater level increases.
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In this research publication, researchers investigated the formation, vegetation succession, and carbon balance of peatland margins in Finnish Lapland. This study leverages HydroGeoSphere (HGS) alongside paleoecological records and remote sensing to address long-standing challenges in understanding how new peatland areas initiate, expand, and influence climate through carbon cycling.
Traditional research on peatlands has focused mainly on central mire areas, with less attention paid to margins where lateral expansion occurs. These frontier zones are critical because their hydrology and vegetation succession determine whether new peatland areas function as carbon sinks or methane sources. By combining peat core analysis, vegetation reconstructions, and HGS-based hydrological modelling, this research provides a detailed picture of how fen margins evolve under different climate and hydrological conditions.
The study found that peat initiation at the Lompolonvuoma fen margin began roughly 2,000 years ago and proceeded in a nonlinear fashion, with multiple patches eventually coalescing. Vegetation succession shifted from sedge–ericaceous communities to Sphagnum-dominated bogs, but some areas remained resilient fen systems due to sustained hydrological inputs. HGS simulations showed that high water tables in fen-type margins are maintained even under drier climates, offering resistance to fen-to-bog transition. This hydrological buffering helps explain why certain margins persisted as methane-emitting fens while others transitioned to carbon-sequestering bogs.
HydroGeoSphere proved essential in linking hydrological processes with ecological outcomes, demonstrating how groundwater–surface water exchanges shape vegetation succession and carbon balance at peatland margins. This research highlights the need to integrate field data with physics-based modelling to better predict the climate feedbacks of peatland expansion.
This work provides critical insights for peatland science and climate research, showing that advanced modelling approaches like HGS can help disentangle the complex drivers of peatland development and improve forecasts of their role in future carbon-climate dynamics.
Abstract:
Peatlands are the most carbon-dense terrestrial ecosystem, and recent studies have shown that the northern peatlands have been (and still are) expanding into new areas. However, depending on the vegetation and hydrological regime in the newly initiated areas, the climate forcing may vary. If these new areas developed as wet fen-type peatlands with high methane emissions, they would initially have a warming effect on the climate. On the other hand, if development began as dry bog-type peatlands, these new peatland areas would likely act as a strong carbon sink from early on. However, although some research has concentrated on the expansion of the new northern peatland areas, there remains a significant lack of studies on the successional development of the newly initiated peatland frontiers. In this research, we combine paleoecological, remote-sensing, and hydrological modeling methods to study the expansion and successional pathway dynamics in a subarctic fen margin in Finnish Lapland and discuss possible implications for the carbon balance of these marginal peatland areas. Our results show that (1) the studied peatland margins started to develop ca. 2000 years ago and have continued to expand thereafter and (2) this expansion has occurred in nonlinear fashion. In addition, wet fen-type vegetation persisted in the studied margin for the majority of the developmental history, and only dryer conditions after the Little Ice Age instigated the fen-to-bog transition. However, a notable part of the fen margins in the Lompolonvuoma and Lompolojänkkä basins has remained wet fen-type vegetation, and the persistence of this vegetation type was likely caused by the hydrological conditions in the peatland and surrounding catchment. Our findings show a large variation in the peatland expansion and succession dynamics, even within a single peatland basin. Although changes in climate conditions initiated the fen-to-bog process in some margins, some vegetation remained in the wet fen stage, showing resilience to allogenic forcings. Thus, when estimating the peatland carbon stocks and predicting the future trajectories for peatland development, this heterogeneity should be taken into account to avoid errors caused by the oversimplification of peatland lateral expansion dynamics.