A Conceptual Model of Soil Susceptibility to Macropore Flow

Abstract

The extent to which a fast, nonequilibrium, and highly transient pore‐scale process such as macropore flow can be predicted is very often debated, although little research has been conducted to investigate this issue. The validity of approaches to “upscaling” transport predictions from pore through Darcy to landscape scales critically depends on the answer to this question. We developed a simple conceptual model of soil susceptibility to macropore flow, based on a synthesis of existing experimental information. The conceptual model takes the form of a decision tree, which classifies soil horizons into one of four susceptibility classes on the basis of easily available site and soil factors. The model was tested against an independent database of tracer breakthrough experiments on undisturbed soil columns collated from the literature (n = 52), using the pore volumes drained at peak solute concentration, tp, as a measure of the strength of macropore flow. Analysis of variance for tp as a function of susceptibility class showed that the overall model was significant. A significant proportion of the residual variation in tp could be attributed to variation in clay content within one of the susceptibility classes. Some important sources of experimental error were also identified that may account for much of the remaining unexplained variation. We concluded that macropore flow is predictable to a sufficient degree from easily available soil properties and site factors. The simple classification tree developed in this study could be used to support hydropedological approaches to quantifying the spatial distribution of contaminant leaching at the landscape scale by providing the basis for class pedotransfer functions to estimate model parameters related to macropore flow. Such an approach has been implemented in the European project FOOTPRINT.

Prediction of biopore- and matrix-dominated flow from X-ray CT-derived macropore network characteristics

“…Various empirical models/pedotransfer functions (e.g., Iversen et al, 2011;Jarvis et al, 2009;Schaap et al, 2001;Wösten et al, 1999;Revil and Cathles, 1999) have been previously proposed for predicting saturated hydraulic conductivity. We have observed poor predictive performance of empirical K sat models such as proposed by Revil and Cathles (1999) and Schaap et al (2001) (Fig.…”

“…), and agricultural management (e.g., plowing) serve as the main channels for this rapid and long-distance flow and transport of water, air, and contaminants. Macropore flow is largely determined by soil structure and is generally a dominating process in loamy and clayey soils (Jarvis et al, 2009) where large inter-aggregate pores and biopores often act as pathways for rapid flow and transport. The transition from matrix to macropore flow (equilibrium to non-equilibrium) depends on the pore size distribution and pore continuity, and the degree of soil saturation (Bouma, 1981).…”

Solute and sediment transport at laboratory and field scale: Contributions of J.-Y. Parlange

“…In this case, in structured soils only a fraction of the stained pores have a role in the transport. Although recently a function for determining the macroporosity was established [Jarvis et al, 2009], it is not possible to predict what paths will take part in the transport, making it difficult to predict leaching of contaminants precisely. Because of this, in practice simple models do as well as the more complicated models.…”

A spatially distributed model of pesticide movement in Dutch macroporous soils

“…Recently, however, progress has been made in this area. Jarvis et al (2009) developed a conceptual model of soil susceptibility to macropore flow. The model took the form of a decision tree, which classifies soil horizons into one of four susceptibility classes on the basis of easily available site and soil factors.…”