Discriminating the Influence of Soil Texture and Management-Induced Changes in Macropore Flow Using Soft X-Rays

Mori, Yasushi; Iwama, Kenji; Maruyama, Toshisuke; Mitsuno, Toru

doi:10.1097/00010694-199907000-00003

Cited by 28 publications

(22 citation statements)

References 17 publications

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“…Other detailed investigations of macropore density in both columns and hillslopes indicate that our assumed value may be at least an order of magnitude lower than many sites (Kitahara, 1989;Mori et al, 1999;Perret et al, 1999;Botschek et al, 2002;Mooney, 2002;Shi et al, 2007). Nevertheless, the example we use falls within the lower end of the density range of visible macropores (½2 mm diameter) found in soil pits within the Hitachi Ohta catchment, Japan (0Ð31-0Ð51%; Noguchi et al, 1997), which contributed significantly to subsurface stormflow during wet antecedent conditions (Sidle et al, 1995a(Sidle et al, , 2000.…”

Section: Model Formulationmentioning

confidence: 58%

How do disconnected macropores in sloping soils facilitate preferential flow?

Nieber

Sidle

2010

Hydrological Processes

110

118

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Abstract:Runoff from hillslopes is generated by processes such as infiltration-excess and saturation overland flow, subsurface stormflow and subsurface return flow. Preferential flow through macropores can affect any one of these runoff generation processes. Field studies at the Hitachi Ohta Experimental Watershed in Japan have noted that self-organization processes may manifest the connectivity of such subsurface flow paths, particularly via macropores, from hillslopes to stream channels. It is well established from soil physics principles that the connectivity of macropore networks depends on soil wetness and this has been shown experimentally at Hitachi Ohta where subsurface flow and streamflow respond to thresholds of wetness. Numerical solutions to the three-dimensional Richards equation are derived for a sloping soil block containing a population of disconnected macropores of various sizes, shapes and orientations. Solutions for the case of steady water flux applied to the surface of the soil block are evaluated to determine the conditions where the disconnected macropores become active in the flow process. Results show that subsurface flow is directed through the preferential flow network in the saturated portion of the soil but bypasses the macropores in the drier regions. The preferential flow network expands as the degree of saturation increases. The expanding network of active macropores leads to less resistance to overall flow in the domain and access to increased volumes of the flow domain. Although the individual macropores are disconnected, it is argued that large localized hydraulic gradients can potentially lead to preferred zones of subsurface erosion. In addition to the importance of these findings related to stormflow generation in catchments, they add support to the concept of self-organization of subsurface flow systems in soils.

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Section: Model Formulationmentioning

confidence: 58%

How do disconnected macropores in sloping soils facilitate preferential flow?

Nieber

Sidle

2010

Hydrological Processes

110

118

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“…Rainfall intensity controls the amount of water available for infiltration and, hence, the saturation of the soil matrix and macropore domain. Bulk density is a readily measured soil property in watershed studies and has been shown to be directly related to macroporosity (e.g., Messing et al, 1997; Mori et al, 1999a,b). For the LME modeling, we included only those experiments with physically plausible parameter estimates (i.e., with 0 < θ o < 1 and with Λ eff20 ≥ 0).…”

Section: Resultsmentioning

confidence: 99%

Developing Risk Models of Cryptosporidium Transport in Soils from Vegetated, Tilted Soilbox Experiments

et al. 2008

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Transport of Cryptosporidium parvum through macroporous soils is poorly understood yet critical for assessing the risk of groundwater contamination. We developed a conceptual model of the physics of flow and transport in packed, tilted, and vegetated soilboxes during and immediately after a simulated rainfall event and applied it to 54 experiments implemented with different soils, slopes, and rainfall rates. Using a parsimonious inverse modeling procedure, we show that a significant amount of subsurface outflow from the soilboxes is due to macropore flow. The effective hydraulic properties of the macropore space were obtained by calibration of a simple two-domain flow and transport model that accounts for coupled flow in the matrix and in the macropores of the soils. Using linear mixed-effects analysis, macropore hydraulic properties and oocyst attenuation were shown to be associated with soil bulk density and rainfall rate. Macropore flow was shown to be responsible for bromide and C. parvum transport through the soil into the underlying pore space observed during the 4-h experiments. We confirmed this finding by conducting a pair of saturated soil column studies under homogeneously repacked conditions with no macropores in which no C. parvum transport was observed in the effluent. The linear mixed-effects and logistic regression models developed from the soilbox experiments provide a basis for estimating macropore hydraulic properties and the risk of C. parvum transport through shallow soils from bulk density, precipitation, and total shallow subsurface flow rate. The risk assessment is consistent with the reported occurrence of oocysts in springs or groundwater from fractured or karstic rocks protected only by shallow overlying soils.

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“…For example, new three‐dimensional computer tomography techniques that combine geometric descriptions of soil macropore structure with continuous real‐time measurements of solute transport show great promise in furthering our detailed knowledge of the processes (e.g. Mori et al , 1999 a ; Perret et al , 2000a,b). Further advances can be expected from research that exploits these and other new experimental techniques to relate macropore structure to observations of solute transport and, ultimately, to model parameters. Fractals should be further explored as a potentially powerful model of structural pore systems and their impacts on macropore flow and transport.…”

Section: Discussionmentioning

confidence: 99%

“…The Reynolds number, which is a measure of the ratio of inertial to viscous forces, exceeds unity and therefore invalidates Darcy's law (Childs, 1969) at pore diameters larger than c. 0.15 mm. Based on real-time measurements of water-flow rates in soil macropores under ponded conditions by soft X-ray radiography, Mori et al (1999a) reported Reynolds numbers varying between 50 and 80 for flow in natural soil macropores under ponded infiltration, which suggested that the flow regime was even transitional to turbulent. Logsdon (1995) reported Reynolds numbers larger than 1000 (i.e.…”

Section: The Physics Of Water Flow and Solute Transport In Macroporesmentioning

confidence: 99%

A review of non‐equilibrium water flow and solute transport in soil macropores: principles, controlling factors and consequences for water quality

Jarvis

2007

European J Soil Science

1,036

589

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This review discusses the causes and consequences of 'non-equilibrium' water flow and solute transport in large structural pores or macropores (root and earthworm channels, fissures and interaggregate voids). The experimental evidence suggests that pores larger than c. 0.3 mm in equivalent cylindrical diameter allow rapid non-equilibrium flow. Apart from their large size and continuity, this is also due to the presence of impermeable linings and coatings that restrict lateral mass exchange. Macropores also represent microsites in soil that are more biologically active, and often more chemically reactive than the bulk soil. However, sorption retardation during transport through such pores is weaker than in the bulk soil, due to their small surface areas and significant kinetic effects, especially in larger macropores. The potential for non-equilibrium water flow and solute transport at any site depends on the nature of the macropore network, which is determined by the factors of structure formation and degradation, including the abundance and activity of soil biota such as earthworms, soil properties (e.g. clay content), site factors (e.g. slope position, drying intensity, vegetation) and management (e.g. cropping, tillage, traffic). A conceptual model is proposed that summarizes these effects of site factors on the inherent potential for non-equilibrium water flow and solute transport in macropores. Initial and boundary conditions determine the extent to which this potential is realized. High rain intensities clearly increase the strength of non-equilibrium flow in macropores, but the effects of initial water content seem complex, due to the confounding effects of soil shrinkage and water repellency. The impacts of macropore flow on water quality are most significant for relatively immobile solutes that are foreign to the soil and whose effects on ecosystem and human health are pronounced even at small leached fractions (e.g. pesticides). The review concludes with a discussion of topics where process understanding is still lacking, and also suggests some potential applications of the considerable knowledge that has accumulated in recent decades.

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Discriminating the Influence of Soil Texture and Management-Induced Changes in Macropore Flow Using Soft X-Rays

Cited by 28 publications

References 17 publications

How do disconnected macropores in sloping soils facilitate preferential flow?

How do disconnected macropores in sloping soils facilitate preferential flow?

Developing Risk Models of Cryptosporidium Transport in Soils from Vegetated, Tilted Soilbox Experiments

A review of non‐equilibrium water flow and solute transport in soil macropores: principles, controlling factors and consequences for water quality

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