The influence of seasonally frozen ground (SFG) on water, energy, and solute fluxes is important in cold climate regions. The hydrological role of permafrost is now being actively researched, but the influence of SFG has received less attention. Intuitively, SFG restricts (snowmelt) infiltration, thereby enhancing surface runoff and decreasing soil water replenishment and groundwater recharge. However, the reported hydrological effects of SFG remain contradictory and appear to be highly site- and event-specific. There is a clear knowledge gap concerning under what physiographical and climate conditions SFG is more likely to influence hydrological fluxes. We addressed this knowledge gap by systematically reviewing published work examining the role of SFG in hydrological partitioning. We collected data on environmental variables influencing the SFG regime across different climates, land covers, and measurement scales, along with the main conclusion about the SFG influence on the studied hydrological flux. The compiled dataset allowed us to draw conclusions that extended beyond individual site investigations. Our key findings were: (a) an obvious hydrological influence of SFG at small-scale, but a more variable hydrological response with increasing scale of measurement, and (b) indication that cold climate with deep snow and forest land cover may be related to reduced importance of SFG in hydrological partitioning. It is thus increasingly important to understand the hydrological repercussions of SFG in a warming climate, where permafrost is transitioning to seasonally frozen conditions.

Undisturbed peatlands are effective carbon sinks and provide a variety of ecosystem services. However, anthropogenic disturbances, especially land drainage, strongly alter peat soil properties and jeopardize the benefits of peatlands. The effects of disturbances should therefore be assessed and predicted. To support accurate modeling, this study determined the physical and hydraulic properties of intact and disturbed peat samples collected from 59 sites (in total 3,073 samples) in Finland and Norway. The bulk density (BD), porosity, and specific yield (Sy) values obtained indicated that the top layer (0–30 cm depth) at agricultural and peat extraction sites was most affected by land use change. The BD in the top layer at agricultural, peat extraction, and forestry sites was 441%, 140%, and 92% higher, respectively, than that of intact peatlands. Porosity decreased with increased BD, but not linearly. Agricultural and peat extraction sites had the lowest saturated hydraulic conductivity, Sy, and porosity, and the highest BD of the land use options studied. The van Genuchten‐Mualem (vGM) soil water retention curve (SWRC) and hydraulic conductivity (K) models proved to be applicable for the peat soils tested, providing values of SWRC, K, and vGM‐parameters (α and n) for peat layers (top, middle and bottom) under different land uses. A decrease in peat soil water content of ≥10% reduced the unsaturated K values by two orders of magnitude. This unique data set can be used to improve hydrological modeling in peat‐dominated catchments and for fuller integration of peat soils into large‐scale hydrological models.

In northern peatlands, near‐saturated surface conditions promote valuable ecosystem services such as carbon storage and drinking water provision. Peat saturated hydraulic conductivity (K_sat) plays an important role in maintaining wet surface conditions by moderating drainage and evapotranspiration. Peat K_sat can exhibit intense spatial variability in three dimensions and can change rapidly in response to disturbance. The development of skillful predictive equations for peat K_sat and other hydraulic properties, akin to mineral soil pedotransfer functions, remains a subject of ongoing research. We report a meta‐analysis of 2,507 northern peat samples, from which we developed linear models that predict peat K_sat from other variables, including depth, dry bulk density, von Post score (degree of humification), and categorical information such as surface microform type and peatland trophic type (e.g., bog and fen). Peat K_sat decreases strongly with increasing depth, dry bulk density, and humification; and increases along the trophic gradient from bog to fen peat. Dry bulk density and humification are particularly important predictors and increase model skill greatly; our best model, which includes these variables, has a cross‐validated r² of 0.75 and little bias. A second model that includes humification but omits dry bulk density, intended for rapid field estimations of K_sat, also performs well (cross‐validated r² = 0.64). Two additional models that omit several predictors perform less well (cross‐validated r² ∼ 0.5), and exhibit greater bias, but allow K_sat to be estimated from less comprehensive data. Our models allow improved estimation of peat K_sat from simpler, cheaper measurements.

Potential benefits of peatland restoration by rewetting include carbon sequestration, restored biodiversity, and improved hydrological functions. There is great uncertainty about how catchment hydrological processes change after restoration, with a particular lack of well‐documented catchment runoff data. This study compared five formerly Disturbed (now Restored) and two undisturbed peatlands. In total, 455 and 728 hydrological events were selected for the analysis, using a three‐event selection technique. Mean event runoff coefficient (RC) values varied greatly between conditions and hydrological events. RC in Disturbed conditions was slightly higher than in undisturbed conditions, but RC in Restored conditions was higher than under other conditions. Mean transit time revealed that event rainfall water reached the outlet faster in Disturbed conditions. Mean event peak flow in Disturbed conditions was higher and peaked faster than under other conditions. However, the base flow showed no noticeable difference between treatments. Significantly higher watertable (WT) rise per rainfall input (0.36–0.85 cm/mm) was observed in Disturbed conditions, due to lower specific yield (Sy) values (0.13–0.24) than under Restored and undisturbed conditions (Sy 0.25–0.50). Shallow WT showed significant positive correlations with runoff and storage properties and was a key component of the runoff generation mechanisms in peatlands. Storage‐related parameters (Sy, WT rise per rainfall input) and catchment response time parameters revealed disturbance‐related hydrological changes in peatlands more clearly than other runoff parameters tested (e.g., RC). Overall, with restoration, WT and storage properties recovered to the levels at undisturbed sites but increased runoff was observed occasionally due to wetter antecedent moisture conditions.