ABSTRACT: Field and laboratory estimation of pore size distributions and water-conducting porosity in organic soils.

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Abstract

Characterizing water-conducting porosity in organic soils in both saturated and unsaturated zones is required for models of water and solute transport. There is a limitation, largely due to lack of data, on the hydraulic properties of unsaturated organic soils, and in particular the relationship between hydraulic conductivity (K) and pressure head (?). Additionally, there is uncertainty as to what fraction of the matrix and what pores conduct water at different pressure heads, as closed and dead-end pores are common features in organic soil. The objectives of this study were to determine the water conducting porosity of organic soils for different pore radii ranges using the method proposed by Bodhinayake et al. (2004) [Soil Sci. Soc. Am. J. 68:760-769] and compare these values to pore size distributions from resin-impregnated laboratory thin sections. Field experiments were completed in the Wolf Creek Research Basin, Yukon, in 2005. Water infiltration rates were measured eight times using a tension infiltrometer at six different pressure heads from -200 to -30 mm. This data was combined with Gardiner’s exponential and van Genuchten-Maulem’s unsaturated hydraulic conductivity function obtained from laboratory drainage curves to provide water conducting porosity for different pore-size ranges. Results indicate that at small pore sizes (~10-5 m), tension and image analysis provide corresponding results of water flux and total pore area. However, as pore size increases (~10-3 m), water conducting porosity as determined via the tension infiltrometer and image analysis diverge, possibly due to the presence of large dead-end pores.

Bibliography of Canadian Geomorphology