Energy and CO2 fluxes in the early stage development of reclaimed and unreclaimed post-mining areas

The carbon exchange in post-mining areas and the impact of various restoration practices—(i) reclaimed (alder plantation on leveled microtopography in 2019) and (ii) unreclaimed (spontaneous development on wave-like microtopography)— on carbon and energy fluxes remains poorly understood. To address this gap, we conducted the first direct measurements of net ecosystem exchange (NEE), latent heat (LE), and sensible heat (H) using paired eddy covariance towers at both reclaimed and unreclaimed sites during the growing seasons of 2020, 2021, and 2023 in the early stage of succession in Czechia. Our novel results show that early post-coal mining sites were net sources of CO₂ but became carbon sinks on a monthly scale within four years, highlighting the rapid ecosystem recovery at both sites. Significant differences in NEE, gross primary production (GPP), ecosystem respiration (Reco), and LE were observed between the two sites. Initially (2020 and 2021), the effect of alder seedlings was negligible. Differences in NEE and LE were mainly caused by higher emissions (Reco) at the unreclaimed site due to lower soil bulk density and higher runoff at the reclaimed site due to compacted soil, both influenced by heavy summer rainfall. By 2023, alder growth (GPP) became the primary factor differentiating the two sites. Climatic variables influenced fluxes similarly at both sites, although correlations were stronger at the unreclaimed site. Our findings suggest that natural succession can lead to CO₂ sinks comparable to alder plantations, offering a practical alternative for post-mining land restoration in Central Europe.