Water content as a function of apparent dielectric permittivity in a Fibric Limnic Humisol

Abstract

Volumetric water content (θv) was estimated from time domain reflectometry (TDR) measurementsof apparent dielectric permittivity (Ka) in an organic soil (Humisol). The goals of this study were: (i) to test the accuracy of existing θv-Ka relationships in this soil and if found insufficient (ii) to develop alternative θv-Ka relationships for this organic soil. The Ka values were measured over a wide range of θv in intact soil cores taken from three horizons (Ohp, Of, Oco). Empirical θv-Ka relationships found in the literature for organic porous media could not accurately describe the θv-Ka relationships of any horizon of this Humisol, probably because of the its very large organic matter content (> 75%) of this soil. New θv-Ka relationships for each horizon were consequently developed. Key words: Organic soil, TDR, coprogenic soil, volumetric water content, apparent dielectric permittivity

Soil‐gas diffusivity in large soil monoliths

“…Soil volumetric water content was slightly larger in the O hp horizon (0.70 m 3 m −3 ) than in the O f horizon (0.57 m 3 m −3 ) in monolith 1 while it was similar in both horizons in monolith 2 and increased from 0.54 to 0.90 m 3 m −3 with depth in monolith 3 (Figure 4). At the bottom of monolith 3, the larger θ v was because of finer fragments of O co (Lange et al ., 2008). Differences in θ v between monoliths resulted in 12 and 16% of variation for O hp and O f , respectively, and in 5 to 15% of variation within monolith for each horizon (Table 1).…”

“…For the mineral soil, particle density (ρ s ) was assumed to be 2.65 mg m −3 (Flint & Flint, 2002a). The ρ s of the organic soil (1.54, 1.52 and 1.48 mg m −3 for O hp , O f and O co , respectively) was measured using a gas pycnometer (AccuPyc 1330, Micromeritics, Norcross, GA, USA) (Flint & Flint, 2002a) as described in Lange et al . (2008).…”

“…It is important to note that monolith 3 contained a third horizon, in contrast to monoliths 1 and 2 (Table 1). These variations between monoliths in horizon thickness were in agreement with those observed in Lange et al . (2008).…”

Application of ground‐penetrating radar to measure near‐saturation soil water content in peat soils

“…For comparison, Figure 5 shows predictions by the models of Topp et al [1980], Kellner and Lundin [2001], and Pepin et al [1992] together with the multiphase mixing model as previously used to estimate θ in peat by Comas et al [2008] and Parsekian et al [2010]. As previously reported, the Topp equation [ Topp et al , 1980] is not optimal for describing the θ of organic soil [e.g., Lange et al , 2008]; however, our data fall close to several of the empirical models developed specifically for this purpose [e.g., Kellner and Lundin , 2001; Pepin et al , 1992]. As per the results of Kellner and Lundin [2001], each of our samples follows a slope within the same order of magnitude to our linear models; however, there are differences in where that trend falls on the θ axis.…”

“…Previous studies on peat soils primarily focus on calibrating the TDR instrument to θ in peat using polynomial models [e.g., Lange et al , 2008; Pepin et al , 1992; Roth et al , 1992] and multiphase dielectric mixing models [e.g., Kellner and Lundin , 2001]. Ground‐penetrating radar instrumentation can be used for the same purpose because both methods provide estimates of permittivity [ Comas and Slater , 2007].…”