Aspect and soil textural controls on snowmelt runoff on forested Boreal Plain hillslopes

Plot studies were conducted on a jack pine forest with sandy soil and aspen forests with sandy and loam soils to examine the controls of slope aspect, soil texture and fall soil moisture content on near-surface snowmelt runoff and infiltration. It was hypothesized that near-surface runoff would be greater from north-facing slopes on loam soils with increased fall soil moisture content. Fall soil moisture had no measurable effect on spring snowmelt runoff. Infiltration of snowmelt dominated (drainage coefficients 53-100%, median 87%) over near-surface runoff (runoff coefficients 1-65%, median 7%) for most plots. Runoff was related to concrete frost at the mineral soil surface. In contrast to the processes hypothesized, south-facing hillslopes with sandy soils generated greater runoff than north-facing slopes or sites with finer-textured soils. These results were due to greater concrete frost development resulting from periodic spring snowmelt and re-freezing in the upper soil. South-facing hillslopes with sandy soils featured lower canopy cover, allowing greater solar radiation to reach the snow surface which led to the formation of concrete frost and faster melt rates resulting in near-surface runoff. Where hillslopes are connected to receiving surface waters by continuous concrete frost, snowmelt runoff at the watershed scale may be enhanced.