Abstract
Abstract. The companion paper (Guan et al., 2010) demonstrated variable interactions and correlations between shallow soil moisture and ground thaw in soil filled areas along a wetness spectrum in a subarctic Canadian Precambrian Shield landscape. From wetter to drier, these included a wetland, peatland and soil filled valley. Herein, water and energy fluxes were examined for these same subarctic study sites to discern the key controlling processes on the found patterns. Results showed the presence of surface water was the key control in variable soil moisture and frost table interactions among sites. At the peatland and wetland sites, accumulated water in depressions and flow paths maintained soil moisture for a longer duration than at the hummock tops. These wet areas were often locations of deepest thaw depth due to the transfer of latent heat accompanying lateral surface runoff. Although the peatland and wetland sites had large inundation extent, modified Péclet numbers indicated the relative influence of external and internal hydrological and energy processes at each site were different. Continuous inflow from an upstream lake into the wetland site caused advective and conductive thermal energies to be of equal importance to ground thaw. The absence of continuous surface flow at the peatland and valley sites led to dominance of conductive thermal energy over advective energy for ground thaw. The results suggest that the modified Péclet number could be a very useful parameter to differentiate landscape components in modeling frost table heterogeneity. The calculated water and energy fluxes, and the modified Péclet number provide quantitative explanations for the shallow soil moisture-ground thaw patterns by linking them with hydrological processes and hillslope storage capacity.
Highlights
Over 50% of Canada’s land surface is underlain with discontinuous or continuous permafrost (Wolfe, 1998). This has profound implications for the hydrology of much of the country because while water can flow in frozen soil, its rate of movement is slowed, and consequentially, lateral and vertical subsurface water fluxes are largely concentrated in the thawed portions above the frost table
At the intra-site scale, the absence of surface water accumulation at the valley site led to very different soil moisture and thaw patterns from those observed at the peatland and wetland sites
Results showed that the relative topology, topography and typology influences at each site dictated the energy and water flux controls on shallow soil moisture and ground thaw
Summary
Over 50% of Canada’s land surface is underlain with discontinuous or continuous permafrost (Wolfe, 1998). This has profound implications for the hydrology of much of the country because while water can flow in frozen soil, its rate of movement is slowed, and consequentially, lateral and vertical subsurface water fluxes are largely concentrated in the thawed portions above the frost table. The water table depth in the peat partly controls the area contributing to runoff As it drops with ground thaw, it causes the contributing area to decrease due to an increase in subsurface storage capacity (Quinton and Marsh, 1999). When the water table position is close to the surface, source areas increase with decreasing flow resistance through the porous organic soils and along hollows (Quinton and Marsh, 1999)
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