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Obligatory mine reclamation efforts in the Athabasca oil sands region require leased land to be returned to pre-disturbance function. This entails the re-establishment of key ecosystem services such as carbon sequestration and water and nutrient cycling. Surface-atmosphere exchanges of energy, heat and moisture are critical to ecohydrological processes and feedbacks that govern ecosystem functionality. Eddy covariance and remote sensing measurements were used to examine the temporal changes in energy partitioning of a reclaimed fen-upland watershed during the initial seven years post-construction (2013–2019). Surface conditions evolved from bare ground to robustly vegetated plant communities, altering albedo, surface roughness and plant-mediated shading. Initially in the fen, due to near-surface water table, high soil moisture content and the low albedo (0.09) of bare, wet peat, energy was predominantly partitioned to latent heat (Q E) and exhibited a high degree of decoupled surface-atmosphere conditions (surface-atmosphere decoupling factor (Ω) of 0.49). As the fen plant community developed and stabilized, Q E remained the dominant energy flux, but a larger proportion of available energy was partitioned to sensible heat flux (Q H). Plant establishment altered the biophysical surface through sheltering and shading affecting ground heat flux and supressing surface evaporative losses. Moreover, plant-mediated water loss through stomatal controls resulted in an increase in surface-atmosphere coupling (Ω = 0.32), particularly during drier periods. In the drier upland, plant emergence and establishment was slower than in the fen. Initially, bare ground in the upland resulted in higher albedo (0.20–0.25), and Q E and Q H were similar. Once understory and tree species matured, Q E increased with seasonal trends that mirrored plant phenology. Unlike the fen, the upland continually exhibited a higher degree of surface-atmosphere coupling (Ω ranging between 0.23 and 0.3). By year seven (2019) energy fluxes and intra- and inter-seasonal trends at the constructed watershed were comparable to natural and post-disturbance boreal landscapes indicating the system is evolving towards a functional, reclaimed ecosystem. [Display omitted] • Surface energy fluxes during the initial seven years following reclamation • During bare ground conditions edaphic and atmospheric controls drove energy fluxes • Plant development altered biophysical surface properties, changing albedo • Energy partitioning shifted and exhibited strong biotic controls • By year seven energy dynamics were comparable to that of natural boreal landscapes [ABSTRACT FROM AUTHOR]

Abstract: The cold climate of Fennoscandia allows soils to experience ephemeral freezing and snow cover. Snowmelt impacts on runoff and solute transport, but is also one of the most important contributors to recharge of ground water reserves. The presence of a snowpack governs the length of a growing season, but limited information is available on the response of partially frozen soil to mild climatic events in winter. We studied time series of soil temperature and unfrozen soil water content during freezing cycles and mild climatic events during two climatically contrasting winters (2001–2002, 2002–2003) at five sites differing in texture and hydraulic features in Finland. Frost penetration was found to be attributable to snowpack thickness, such that soil temperatures seldom fell below −1.5 °C, when a snow cover of more than 30 cm was present. Soil surface temperatures can fall below 0 °C and soil water freezes to 10-cm depth, but soil water is predominantly unfrozen during winter in deeper soil horizons, 30- to 90-cm depths. Water released by snowmelt during mild climatic events in winter was observed to infiltrate through partially frozen soil, hence contributing significant recharge to ground water resources. [Copyright &y& Elsevier]