Basin bathymetry controls the long-term carbon accumulation in northern boreal sloping fen

Boreal peatlands play a crucial role in global carbon dynamics as sinks and sources. Groundwater dependent nutrient rich sloping fen ecosystem is a typical morphological peatland type for northeastern Finland. To increase the understanding of the carbon dynamics of these ecosystems we investigate the long-term carbon accumulation pattern in sloping fen in the carbonate bedrock area in northern boreal zone. 

The study site Puukkosuo is a sloping fen situated in Oulanka in northern boreal zone in NE Finland. Four peat cores were obtained across the study site. All cores were radiocarbon dated for chronological control to calculate the peat accumulation rate. Peat characteristics (peat composition, humification degree, bulk density) and carbon content was analysed to investigate the development of the peatland and long-term carbon storage during the Holocene. The peat accumulation rate, based on radiocarbon dates, bulk density and carbon content were used to calculate the long-term carbon accumulation. To assess the role of basin bathymetry to peatland development and carbon storage, the 3D structure of the Puukkosuo basin was modelled with Leapfrog Geo (Seequent) program based on network of ground penetrating radar (GPR) profiles (5.5 km) across the peatland and reference peat stratigraphy. 

The records cover the last 9 000 cal yr BP of peatland development and carbon accumulation. The results suggests that the carbon accumulation rate in the basal part of the basin exceeds the average rate in the northern boreal zone, whereas the surface layer demonstrates typical carbon accumulation values. The changes in the accumulation rate are divergent between cores but occur at the same altitudinal level of the basin. Therefore, we conclude that here the bathymetry rather than the accumulation period controls the major carbon accumulation patterns. These results will be further discussed in the presentation.