【饱和非饱和土壤中液相和气相扩散模型】Shoichiro Hamamoto ^*a Per Moldrup^b Ken Kawamoto^c and Toshiko Komatsu^c. Maxwell’s Law Based Models for Liquid and Gas Phase Diffusivities in Variably-Saturated Soil. SSSAJ Vol. 76 No. 5 p. 1509-1517

Abstract

The gas diffusion coefficient (D_sg) and solute diffusion coefficient (D_sl) and their dependencies on fluid content (κ) (equal to soil–air content θ for D_sg and soil–water content ɛ for D_sl) are controlling factors for gas and solute transport in variably saturated soils. In this study we propose unified predictive models for D_sg(ɛ) and D_sl(θ) based on modifying and extending the classical Maxwell model at fluid saturation with a fluid-induced reduction term including a percolation threshold (ɛ_th for D_sg and θ_th for D_sl). Different percolation threshold terms adopted from recent studies for gas (D_sg) and solute (D_sl) diffusion were applied. For gas diffusion ɛ_th was a function of bulk density (total porosity) while for solute diffusion θ_th was best described by volumetric content of finer soil particles (clay and organic matter) FINES_vol. The resulting LIquid and GAs diffusivity and tortuosity (LIGA) models were tested against D_sg and D_sl data for differently-textured soils and performed well against the measured data across soil types. A sensitivity analysis using the new Maxwell’s Law based LIGA models implied that the liquid phase but not the gaseous-phase tortuosity was controlled by soil type. The analyses also suggested very different pathways and fluid-phase connectivity for gas and solute diffusion in unsaturated soil. In conclusion the commonly applied strategy of using the same soil-type-independent model for gas and solute diffusivity in analytical and numerical models for chemical transport and fate in variably-saturated soils appears invalid except for highly sandy soils. The unified LIGA model with differing percolation thresholds for diffusion in the liquid and gaseous phases solves this problem.

【土壤粘粒含量的估算】Mark N. Wuddivira ^*a David A. Robinson^b Inma Lebron^b Laëtitia Bréchet^c Melissa Atwell^d Sunshine De Caires^d Michael Oatham^e Scott B. Jones^f Hiruy Abdu^f Aditya K. Verma^g and Markus Tuller^g. <