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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: C-band Radarsat-2 data were used to develop multi-parameter algorithms to retrieve soil moisture across a chronosequence (recently burned, shrubby regrowth and mature forest) of fire-disturbed Alaskan boreal black spruce forests using polarized backscatter intensity, polarimetric decomposition and discriminator parameters as independent variables. To account for complex interactions of surface roughness, biomass and soil moisture, multiple polarimetric variables were evaluated empirically in algorithm development using a time series dataset that included the wet and dry extreme conditions. Results indicate that polarimetric discriminators, such as maximum degree of polarization, fractional polarization or coefficient of variation, may be instrumental in accounting for the type of scattering occurring or the complexity or heterogeneity of the distributed target. Using the maximum degree of polarization combined with one or more variables on scattered intensity (e.g. C-HV, C-HH, or maximum scattering intensity) improved multi-linear moisture retrieval algorithms by 27–33% over the single, dual and quad polarized backscatter intensity algorithms. For all sites combined, algorithms were developed with low SE (7.0% volumetric soil moisture), moderately high R2 (0.77) and low RMSE (6.7% volumetric soil moisture). However, the best models were produced by separating the recently burned forests (strongest algorithm: R2 0.94, SE 5.9, RMSE 7.4) from the shrubby and mature forests (best algorithm: R2 0.85, SE 4.7, RMSE 7.3). Results are limited to sites with biomass below 3kg/m2. [Copyright &y& Elsevier]

Abstract: Climate change may cause a decrease in snow cover in northern latitudes. This, on the other hand, may result in more severe soil frost even in areas where it is not common at present, and may lead to increased stress on the tree canopy. We studied the effects of snow removal and consequent changes in soil frost and water content on the physiology of Norway spruce (Picea abies [L.] Karst.) needles and implications on root biomass. The study was conducted at a 47-year-old Norway spruce stand in eastern Finland during the two winters of 2005/06 and 2006/07. The treatments in three replicates were: (i) natural snow accumulation and melting (CTRL), (ii) artificial snow removal during the winter (OPEN), and (iii) the same as OPEN, but the ground was insulated in early spring to delay soil thawing (FROST). In spite of the deeper soil frost in the OPEN than in the CTRL treatment, soil warming in spring occurred at the same time, whereas soil warming in the FROST was delayed by 2 and 1.5 months in 2006 and 2007, respectively. The soil water content was affected by snow manipulations, being at a lower level in the OPEN and FROST than CTRL in spring and early summer. The physiological measurements of the needles (e.g. starch, carbon and nitrogen content and apoplastic electrical resistance) showed differences between soil frost treatments. The differences were mostly seen between the CTRL and FROST, but also in the case of the starch content in early spring 2007 between the CTRL and OPEN. The needle responses in the FROST were more evident after the colder winter of 2006. The physiological changes seemed to be related to the soil temperature and water content in the early growing season rather than to the wintertime soil temperature. No difference was found in the fine root (diameter<2mm) biomass between the treatments assessed in 2007. In the future, conditions similar to the OPEN treatment may be more common than at present in areas experiencing a thick snow cover. The present experiment took place over the course of two years. It is possible that whenever thin snow cover occurs yearly, the reduced starch content during the early spring may be reflected in the tree growth itself as a result of reduced energy reserves. [Copyright &y& Elsevier]

Abstract: Soil water content strongly affects permafrost dynamics by changing the soil thermal properties. However, the movement of liquid water, which plays an important role in the heat transport of temperate soils, has been under-represented in boreal studies. Two different heat transport models with and without convective heat transport were compared to measurements of soil temperatures in four boreal sites with different stand ages and drainage classes. Overall, soil temperatures during the growing season tended to be over-estimated by 2–4°C when movement of liquid water and water vapor was not represented in the model. The role of heat transport in water has broad implications for site responses to warming and suggests reduced vulnerability of permafrost to thaw at drier sites. This result is consistent with field observations of faster thaw in response to warming in wet sites compared to drier sites over the past 30years in Canadian boreal forests. These results highlight that representation of water flow in heat transport models is important to simulate future soil thermal or permafrost dynamics under a changing climate. [Copyright &y& Elsevier]

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]