Core Ideas Determining unsaturated hydraulic conductivity in highly compressible porous media. Method comparison between uniform and non-uniform soil water pressure gradients. Hydrophysical parameter measurement in living and undecomposed Sphagnum moss. Update on Price et al 2008 (DOI: 10.2136/sssaj2007.0111N) and improvements to method. Highly compressible soil, such as Sphagnum moss and peat, undergo volume change with varying volumetric soil water content (θ) and pressures (ψ), so typical methods for determining unsaturated hydraulic conductivity (Kunsat) in non-compressible mineral soils can be problematic. However, characterizing these relationships are essential for modeling ecohydrological processes. Two methods have been developed for determining Kunsat of these highly compressible soils using "floating" tension disks; the original method imposes a ψ gradient across a sample, while a modified method imposes no ψ gradient and flow is driven by gravity. However, it is unknown if they produce comparable results. Milled horticultural peat was compressed (n = 34) to a bulk density of 0.19 ± 0.01 g cm-3 and Kunsat and θ were measured for each sample at variable ψ-steps (−5, -10, -15, and -25 cm) for both methods. In the modified method average θ was found to be lower (p < 0.001, df = 19) at ψ-steps -10 and -15 cm, while average Kunsat was lower (p < 0.001, W = 210) at all ψ-steps. Numerical modeling (Hydrus-1D) of each ψ-step identified nonlinear distributions of ψ, θ, and Kunsat within a sample in the original method (verified with tensiometer measurements), whereas a uniform distribution of these parameters was observed in the modified method. We conclude the modified method produces a more precise measurement of the K(ψ) function. Although these methods were developed for Sphagnum moss and peat soils, the method can likely be used for other compressible or delicate media.
Establishing hydrological connectivity in reconstructed landscapes, and understanding how this connectivity evolves over time, is critical for the development of effective water management strategies after oil sands extraction. In the current study, the dominant controls on the soil water regimes and runoff generation mechanisms on two contrasting reclaimed slopes (2 and 6 years after reclamation) in the Athabasca oil sands region are investigated. The most recently reclaimed slope demonstrated a hydrologic regime with limited soil water storage due to a low surface infiltration capacity that constrained percolation of rainfall. Accordingly, this slope generated a substantial amount of surface runoff controlled primarily by precipitation intensity. Conversely, the older slope had a greater surface infiltration capacity, more dynamic soil water regime, and infrequent surface runoff. Topography controlled soil water distribution on the older slope more strongly than the newer slope due to more efficient water redistribution. This suggests that changes in the hydrophysical properties of reclamation materials following construction result in a shift in the hydrological role of reclaimed slopes at the watershed scale. Thus, over time, reclaimed slopes produce less overland flow and shift from water conveyors to water storage features in constructed watershed systems.
Abstract In northern peatlands, near‐saturated surface conditions promote valuable ecosystem services such as carbon storage and drinking water provision. Peat saturated hydraulic conductivity ( K sat ) plays an important role in maintaining wet surface conditions by moderating drainage and evapotranspiration. Peat K sat can exhibit intense spatial variability in three dimensions and can change rapidly in response to disturbance. The development of skillful predictive equations for peat K sat and other hydraulic properties, akin to mineral soil pedotransfer functions, remains a subject of ongoing research. We report a meta‐analysis of 2,507 northern peat samples, from which we developed linear models that predict peat K sat from other variables, including depth, dry bulk density, von Post score (degree of humification), and categorical information such as surface microform type and peatland trophic type (e.g., bog and fen). Peat K sat decreases strongly with increasing depth, dry bulk density, and humification; and increases along the trophic gradient from bog to fen peat. Dry bulk density and humification are particularly important predictors and increase model skill greatly; our best model, which includes these variables, has a cross‐validated r 2 of 0.75 and little bias. A second model that includes humification but omits dry bulk density, intended for rapid field estimations of K sat , also performs well (cross‐validated r 2 = 0.64). Two additional models that omit several predictors perform less well (cross‐validated r 2 ∼ 0.5), and exhibit greater bias, but allow K sat to be estimated from less comprehensive data. Our models allow improved estimation of peat K sat from simpler, cheaper measurements.
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