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Thermal Properties of Peaty Soils: Effects of Liquid-Phase Impedance Factor and Shrinkage

Author:
Dissanayaka, Shiromi Himalika, Hamamoto, Shoichiro, Kawamoto, Ken, Komatsu, Toshiko, Moldrup, Per
Source:
Vadose zone journal 2012 v.11 no.1
ISSN:
1539-1663
Subject:
air drying, greenhouse gas emissions, heat, impedance, marshes, microbial activity, organic soils, prediction, shrinkage, soil horizons, soil profiles, soil water, statistical models, thermal conductivity, vadose zone, water content, Japan
Abstract:
Soil thermal conductivity (λ) and heat capacity (C) control heat transport and the thermal environment for biogeophysical processes in the vadose zone. Accurate λ and C predictions for peaty soils with high organic contents are particularly important for assessing emissions of greenhouse gases formed during microbial activity in wetlands. In this study, we measured the λ and C at different soil-water matric potentials on undisturbed samples for three peaty soil profiles at the Hokkaido Bibai marsh in Japan, representing a total of 10 different soil horizons. The thermal properties under air-dried conditions, λdry and Cdry, were measured separately at changing volumetric solids contents (σ). For each sample, volume shrinkage was observed to varying degrees during the drying process. Measured λ and C increased linearly with increasing volumetric water content (θ). Applying the concept of a three-phase mixing model and incorporating the λ-θ or C-θ and the λdry-σ or Cdry-σ relations, predictive λ and C models were developed as functions of σ and θ . The new mixing model is represented by λ = λdry + fλθλw and C = Cdry + fCθCw, where λw and Cw are the thermal conductivity and heat capacity of water, respectively, and f is an impedance factor that takes into account the liquid-phase tortuosity. The new mixing model predicted literature λ-θ data on peaty and highly organic soils under variable saturation well. The probable ranges of λ and C under variable saturation were proposed based on the sensitivity analysis.
Agid:
311249