Seasonal variation of soil erodibilities in southwestern Quebec

Abstract

Fallow surface runoff plots were monitored from September 1, 1983, to August 31, 1985, to assess the seasonal variability in erodibility of four Quebec soils: a St. Bernard sandy loam (Orthic Melanic Brunisol; Typic Eutrochrept), a Chicot sandy loam (Gleyed Sombric Brunisol; Umbric Dystrochrept), a Rideau clay (Orthic Humic Gleysol; Typic Humaquept), and a St. Damase loamy sand (Orthic Humo-Ferric Podzol; Aquic Haplorthod). The condition of the soils was classified into one of four categories for each runoff event: summer, winter-frozen, winter-partially frozen, and winter-thawed, based on the time of year and the presence of frost in the soil at the time of the event. Tipping-bucket flowmeters attached to digital recorders measured runoff volumes and runoff rates. Soil loss was determined on a per-event basis. Per-event soil erodibilities were calculated using a modified version of the universal soil loss equation. The mean erodibilities of partially frozen soils were consistently highest of the soil conditions tested, generally by an order of magnitude or more. Large differences among means were required for statistical significance due to the large variability in the data. The results imply that the USLE may underestimate snowmelt-caused and annual soil loss from soils where runoff occurs while soils are partially frozen.