Portal de Periódicos da CAPES

GAS TRANSPORT PARAMETERS ALONG FIELD TRANSECTS OF A VOLCANIC ASH SOIL

2007; Lippincott Williams & Wilkins; Volume: 172; Issue: 1 Linguagem: Inglês

10.1097/01.ss.0000235850.55944.04

1538-9243

Augustus C. Resurreccion, Ken Kawamoto, Toshiko Komatsu, Per Møldrup, Noriatsu Ozaki, Dennis E. Rolston,

Landfill Environmental Impact Studies

Variations in gas transport parameters at the field scale govern the transport, fate, and emission of greenhouse gases and volatile organic chemicals in soil. In this study, we evaluated predictive models for soil-gas diffusivity (Dp/Do) and air permeability (ka) based on measurements along a 117-m transect and a parallel 33-m transect of a humic volcanic ash soil (Andisol) in Nishi-Tokyo, Japan. Measurements were done on 100-cm3 undisturbed soil samples, with 3-m spacing between sampling points, and included water retention, soil-gas diffusion coefficient (Dp), ka at different soil-water matric potentials, and saturated hydraulic conductivity. Traditionally used predictive gas diffusivity models underestimated Dp/Do in wet soil and largely overestimated Dp/Do under dry conditions because of soil aggregation effects. A linear model for Dp/Do as a function of air-filled porosity (ε), taking into account inactive/remote air-filled pore space, accurately described Dp(ε)/Do from wet to oven-dry conditions and well captured the spatial variations in Dp/Do along the transects. The ka exhibited a nonlinear relation with ε, and ka(ε) was best predicted from a recently presented power-law model, with measured ka at −100 cm H2O of soil-water matric potential (ka,100) as a reference point. Trends of decreasing soil-water retention and increasing ε along transects were observed. Similar trends in ka and saturated hydraulic conductivity were not observed because the convective fluid transport parameters were mainly governed by soil structure and not by fluid phase contents. Autocorrelograms suggested a spatial correlation range of 10 to 20 m for gas transport parameters (Dp/Do and ka). Measurements of ε and ka at conditions close to −100 cm H2O of soil-water matric potential are suggested for rapid assessment of the magnitude and spatial variations in gas transport properties at the field scale.