Peat hydraulic conductivity in cold regions and its relation to pore size and geometry

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Subsurface flow through peat plays a critical role in the hydrology of organic-covered, permafrost terrains, which occupy a large part the continental arctic, sub-arctic, and boreal regions. Hillslope drainage in these terrains occurs predominantly through the active flow zone between the relatively impermeable frost table and the water table above it. The hydraulic conductivity profile within this zone controls the subsurface drainage of snowmelt and storm water. Peat hydraulic conductivity profiles were examined at three sites in north-western Canada, each representing a widely occurring organic-covered, permafrost terrain type. Three independent measures of saturated hydraulic conductivity were used—tracer tests, constant-head wellpermeameter tests, and laboratory measurements of undisturbed samples. At all three sites, the conductivity profiles contained very high values (10–1000 m d-1) within the top ca 0.1 m where the peat is only lightly decomposed, a large reduction with increasing depth below the ground surface in the transition zone, and relatively low values in a narrow range (0.5–5 m d-1) below ca 0.2 m depth, where the peat is in an advanced state of decomposition. Digital image analysis of resin-impregnated peat samples showed that hydraulic conductivity is essentially controlled by pore hydraulic radius. The strong dependence of hydraulic conductivity on hydraulic radius implies that peat soils subjected to similar degrees of decomposition and compaction have a similar hydraulic conductivity regardless of the location. This explains the similarity of the depth-conductivity profiles among all three terrain types.

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