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Water repellency by laboratory burning of four northern Rocky Mountain forest soils
Robichaud, P. R.; Hungerford, R. D. 2000.
Water repellency by laboratory burning of four northern Rocky Mountain forest soils.
Journal of Hydrology. 231-232(2000): 207-219.
Keywords: hydrophobicity, soil heating, water drop penetration time, water repellent, water repellency
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Abstract:
Highly variable water repellent soil conditions have been reported after forest fires. We examined
interactions among heating, soil water content and soil texture on water repellency. Undisturbed, 305-mm
diameter cores were collected in the field from four soils commonly referred to as ash-cap, mixed ash-cap, no
ash-cap and granitic soils. Three artificial burning treatments and a control (no heat) and two soil water contents
were evaluated under laboratory conditions. Twenty water drops were placed on each soil layer starting at the
surface and continuing at 10 mm intervals to a depth of 70 mm, and the times to infiltrate were recorded. The
dry control treatment was more water repellent than the wet control treatment. The dry, low heat treatment was
the most repellent, 10 to 20 mm below the soil surface with mean water drop penetration times greater that 60 s.
Repellency decreased as the heating increased. In wet soils of the high heat treatment, a water repellent layer was
generally detected 30 to 50 mm below the soil surface. Presumably, hydrophobic substances were translocated
along the temperature gradient which cooled at depth (< 50 mm) causing condensation on the soil particles.
Water repellency after prescribed fire would probably be minimal because long heating times are not common.
Moscow FSL publication no. 2000f
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