Abstract:To predict the long-term sustainability of water resources on the Boreal Plain region of northern Alberta, it is critical to understand when hillslopes generate runoff and connect with surface waters. The sub-humid climate (P Ä ET) and deep glacial sediments of this region result in large available soil storage capacity relative to moisture surpluses or deficits, leading to threshold-dependent rainfall-runoff relationships. Rainfall simulation experiments were conducted using large magnitude and high intensity applications to examine the thresholds in precipitation and soil moisture that are necessary to generate lateral flow from hillslope runoff plots representative of Luvisolic soils and an aspen canopy. Two adjacent plots (areas of 2Ð95 and 3Ð4 m 2 ) of contrasting antecedent moisture conditions were examined; one had tree root uptake excluded for two months to increase soil moisture content, while the second plot allowed tree uptake over the growing season resulting in drier soils. Vertical flow as drainage and soil moisture storage dominated the water balances of both plots. Greater lateral flow occurred from the plot with higher antecedent moisture content. Results indicate that a minimum of 15-20 mm of rainfall is required to generate lateral flow, and only after the soils have been wetted to a depth of 0Ð75 m (C-horizon). The depth and intensity of rainfall events that generated runoff >1 mm have return periods of 25 years or greater and, when combined with the need for wet antecendent conditions, indicate that lateral flow generation on these hillslopes will occur infrequently.

Redding, T. E. and Devito, K. J. 2006. Particle densities of wetland soils in northern Alberta, Canada. Can. J. Soil Sci. 86: 57-60. Particle density is a fundamental soil physical property, yet values of soil and organic matter particle density (ρ s and ρ o ) vary widely in the literature. We measured particle density of organic soils from five wetland types, and from exposed sediments of drying ponds, in northern Alberta, Canada. Our measured values of organic soil and pond sediment ρ s varied widely (1.43-2.39 Mg m -3 ); however, calculated values of ρ o (1.34-1.52 Mg m -3 ) were relatively constant. The measured and calculated ρ s and ρ o values were similar to those obtained in published studies using similar methods, but were higher than the values provided in many reference texts. Given the relatively small variability in ρ o , the use of mean values of ρ o , combined with measurements of organic matter loss-on-ignition, shows promise as a simple method for obtaining reliable estimates of ρ s across a range of wetland types. The physical properties (e.g., bulk density, particle density, porosity, organic carbon content) of surface soils exert a strong influence on the exchanges of energy and water between the atmosphere and deeper soils (Baldocchi et al. 2000). Data on particle density (ρ s ), the mass of solids per unit volume of solids (Brady and Weil 1999), is of particular importance in hydrological studies because ρ s is required for the calculation of porosity and heat capacity. Specific applications of particle density data include the measurement and modelling of soil thermal conductivity and heat capacity (de Vries 1963), quantification of shrink-swell behaviour of wetland soils (Price 2003), and calculation of surface saturation and hydrological connectivity from remotely sensed soil moisture data (Wolniewicz 2002).Values of wetland soil ρ s reported in the literature range from 0.84 to 1.67 Mg m -3 (Table 1). The ρ s of wetland soils is a function of the relative proportions of organic (ρ o , organic matter particle density) and mineral materials (ρ m , mineral particle density) present in the soil. While ρ m is generally assumed to be 2. (Table 1). Values of ρ s for wetland soils are not provided in common wetlands reference texts (e.g., Mitsch and Gosselink 2000) or hydrology reference texts (e.g., Dingman 2002), while soils reference texts tend to concentrate on mineral soils from an agricultural perspective (e.g., Brady and Weil 1999; Skopp 2002). The primary literature contains measurements of ρ s and ρ o made with pycnometers that are fairly consistent between wetland types and geographical locations (Table 1), but are at odds with the values presented in common reference texts (Brady and Weil 1999; Skopp 2002;Lide 2002). Given the wide range of ρ o and wetland ρ s values reported in the literature, it is difficult to know which values to employ for the variety of wetland types encountered on the Boreal Plain of northern Alberta, Canada. The objectives of this research were to determine ...

To investigate if timber harvesting influences spatial patterns of soil microclimate, forest floor soil temperature and moisture were examined across forest-clearcut edges. Transects were sampled during the 2000 growing season across a 1-ha clearcut at a subalpine forest site in the southern interior of British Columbia, Canada. Forest floor temperature measurements were made twice, once under sunny and once under overcast conditions. Moisture status, measured under wet and dry conditions, was expressed as gravimetric and volumetric moisture content and matric potential. Wavelet analysis was used to detect and compare the location of edges in soil properties, and variance partitioning was used to examine the environmental and spatial sources of variability in temperature and moisture. Based on the wavelet analyses, the transition zone, in both temperature and moisture between forest and clearcut occurred at 7-15 m into the clearcut from the south edge and at 8-18 m into the forest from the north edge. Spatial patterns were consistent between clear and overcast conditions and wet and dry conditions. Distance from the edge was a minor source of spatial variability in temperature and moisture relative to the strong contrast between forest and clearcut conditions. The edge influences may have implications for nutrient cycling, plant available water and forest regeneration. Can. J. Soil Sci. 83: 121-130. Les auteurs ont étudié l'incidence de la zone de transition entre les secteurs coupés à blanc et la forêt sur la température et la teneur en eau du sol forestier afin d'établir si la récolte du bois modifie le profil spatial du microclimat tellurique. Durant la période végétative de 2000, ils ont donc prélevé des échantillons le long de transects dans une zone de coupe à blanc d'un hectare, en bordure d'une forêt subalpine de l'intérieur sud de la Colombie-Britannique, au Canada. La température du sol a été relevée quand il faisait soleil et lorsque le ciel était nuageux, alors que la teneur en eau a été mesurée par temps sec et humide et exprimée en unités gravimétriques et volumétriques ainsi qu'en fonction de la baisse du potentiel hydrique du sol (potentiel matrique). L'analyse des ondelettes a permis de déceler et de comparer les endroits où les propriétés du sol changent. Par ailleurs, les auteurs ont recouru à la séparation des variances pour établir l'origine spatiale ou environnementale des fluctuations de température et de teneur en eau. Selon l'analyse des ondelettes, la zone de transition entre la forêt et les secteurs coupés à blanc pour la température et l'eau s'étend de 7 à 15 m dans le secteur déboisé, au sud de la lisière de la forêt, jusqu'à 8 à 18 m à l'intérieur de la forêt, au nord de sa bordure. Les profils spatiaux sont cohérents, que le ciel soit dégagé ou couvert et le sol, sec ou humide. La distance de part et d'autre du bord de la forêt n'entraîne qu'une faible variation spatiale de la température et de la teneur en eau, comparativement au fort contraste qui existe entre les conditions rele...

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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 nearsurface snowmeit runoff and infiltration. It was hypothesized that near-surface runoff would be greater from north-facing slopes on ioam sous with increased faii soil moisture content. Fali sou moisture had no measurable effect on spring snowmeit 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 minerai sou surface. In contrast to the processes hypothesized, south-facing hiiisiopes with sandy sous 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 snowmeit and re-freezing in the upper soil. South-facing hiiisiopes with sandy soils featured iower 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 hiiisiopes are connected to receiving surface waters by continuous concrete frost, snowmeit runoff at the watershed scaie may be enhanced.