Carbon balance in an abandoned peat extraction area influenced by spatial heterogeneity and vegetation development

• An abandoned, drained peat-extracted area with dense plant growth remains a net carbon source. • Net ecosystem exchange (NEE) is mainly controlled by net radiation and energy fluxes. • The eddy covariance (EC) and closed chamber methods together revealed temporal and spatial variability in fluxes. • Phragmites australis dominated areas in the abandoned peat extraction site, where the highest CH 4 fluxes occur. This study was conducted to determine greenhouse gas (GHG) fluxes and assess the carbon cycle of the ecosystem at an abandoned peat extraction site in Lavassaare, Estonia. Two years of measurements from January 2023 to December 2024 using an eddy covariance (EC) technique and closed chamber measurements showed that the site acts as a carbon source. Annual CO 2 emissions were measured as 84 ± 129 g CO 2 C m -2 y -1 in 2023 and 19 ± 53.2 g CO 2 C m -2 y -1 in 2024. CH 4 emissions were recorded as 1.28 ± 0.64 g CH 4 C m -2 y -1 in 2023 and 1.94 ± 0.69 g CH 4 C m -2 y -1 in 2024. N 2 O emissions measured during chamber campaigns ranged from -0.01 to 0.21 nmol m -2 s -1 , with slightly elevated emissions observed in areas dominated by Betula pendula , while Pinus sylvestris areas exhibited low N 2 O fluxes. Closed chamber data revealed significant spatial heterogeneity, with the highest CH 4 emissions in Phragmites australis areas. Mutual information (MI) analysis indicated NEE correlated primarily with radiation and energy fluxes, while CH 4 fluxes related to soil water content and temperature. Vegetation type also influenced CH 4 emissions, reflecting plant-facilitated transport in Phragmites australis stands. Consistent differences between EC and chamber methods highlighted the importance of spatial heterogeneity and scale. The site is in transition, and favorable conditions, such as a higher water table and continued vegetation recovery, could support a shift to a net carbon sink. Combined EC and chamber methods can provide an enhanced understanding of GHG dynamics and long-term carbon budget assessments of degraded peatlands.