Quantifying Pore‐Size Spectrum of Macropore‐Type Preferential Pathways

Abstract

Both physical and biological processes have temporal and Structural pores associated with macropore-type preferential flow spatial patterns of formation and destruction cycles pathways can accelerate chemical transport in unsaturated soils, thereby potentially causing groundwater contamination. To predict chemical (Gupta et al., 2002). Tillage practices and compaction, transport through these pathways, classical deterministic models de-for example, often destroy the continuity of large strucpend on soil hydraulic conductivity, which effectively lumps flow contural pores (Isensee et al., 1990). The coefficient of varitributions from all individual pathways. We contend, however, that quanation of soil hydraulic conductivity, which is often dictifying the pore spectrum of preferential pathways, without lumping the tated by the soil structural pores, ranged from 100 to contributions of individual pores, is the appropriate method for simu-400% (Libardi et al., 1980; Warrick and Nielsen, 1980). lating convective chemical transport through macropore-type prefer-This suggests that the spatial variability of soil structural ential pathways. In this study, we conducted field-scale experiments pores measured by using core-or block-sized samples is by using an improved tile drain monitoring protocol to measure the very large. As a result, the size spectrum of large strucmass flux breakthrough patterns of conservative tracers. The tails of tural pores measured at several random locations by these patterns suggested that the impact of preferential pathways on contaminant transport can be conceptualized as that occurring through small sample sizes in a field may not represent the speccylindrical capillary tubes. We then proposed a distribution function trum of the entire field. Temporal extrapolation of meabracketed by sharp cutoff points to represent the pore spectrum of surements may be similarly invalid. For these reasons, these tubes. Finally, we used the measured tracer breakthrough curves it is difficult to directly measure the field-scale spectrum (BTCs) as data sources to find the parameters of the proposed funcof the large structural pores, yet this property is among tion. Our results, based on the best fitting, showed that the preferential the most important soil properties when dealing with pathways are naturally clustered into domains; preferential pathways issues related to water quality. with a wide range of pore radii could become active simultaneously Soil characteristic curves and hydraulic conductivity when infiltration rate increases. Because the derived pore spectra sicurves were used in past research from the 1950s and multaneously satisfy both water movement and solute transport, pore 1960s [summarized by Hillel (1980, p. 183-185) and Jury spectra can be used to (i) calculate soil hydraulic conductivity of preferential pathways in deterministic approaches, and (ii) construct multi-et al. (1991, p. 89-94)] to quantify the soil pore-size ple probability density functions (PDFs) for the transfer function ap-d...

Estimation and upscaling of dual-permeability model parameters for the transport of E. coli D21g in soils with preferential flow

“…However, no methodology has been developed to directly characterize the PDF, especially when preferential flow pathways are presented. Kung et al (2005) proposed an indirect method to determine pore-size spectrum of macropore-type preferential pathways, but quantification of PDFs remains a challenge for the application of stochastic models to preferential flow and transport.…”

Efecto De La Labranza Sobre La Porosidad De Un Suelo Arcilloso De Pastizal Estimada Mediante Análisis De Imagen

“…A fraction of the porosity that oscillates between 30 y 43 % wasn't quantified and it is assumed that it would correspond to the micropores, which can only be observed using a scanning electron microscope (MBE). Soils have a spectrum of pores with a radius between 10 -3 y 10 -7 (Kung et al, 2005). It would be expected that immediate tillage would only affect those pores whose radius is close to 10 -3 , where macropores are located.…”

“…Cabe destacar que una fracción de la porosidad que oscila entre 30 y 43 % no fue cuantificada y se asume que correspondería a los microporos que solamente pueden ser observados con el microscopio electrónico de barrido (MEB). De manera natural, los suelos tienen un espectro de poros con radio generalmente entre 10 -3 y 10 -7 (Kung et al, 2005). Se esperaría que la labranza de manera inmediata únicamente afectara aquellos poros cuyo radio es cercano a 10 -3 donde se ubican los macroporos.…”

On the importance of hysteresis and heterogeneity in the numerical simulation of unsaturated flow

“…Akhtar et al (2003a) used dye tracer to visualize flow pattern for unsaturated conditions. Kung et al (2005) conducted field scale experiments by using an improved tile drain monitoring protocol to measure the mass flux breakthrough patterns of conservative tracers. Akhtar et al (2003b) investigated the transport of Cl − and Li + in undisturbed soil columns.…”