Preferential flow and transport in soil: progress and prognosis

Abstract

Soil is the first filter of the world's water; its buffering and filtering determine the quality and quantity of our reserves of subterranean and surface water. Preferential flow can either enhance, or curtail, the capacity of the soil to buffer and filter, and it can compromise, or boost, other ecosystem services. We ask 'when do preferential flow and transport matter?' We identify 12 of 17 ecosystem services that benefit from preferential flow and three that are affected detrimentally. We estimate by simple arithmetic the value of preferential flow to ecosystem services to be globally some US$304 billion (10 9 ) per year. We review the 1989 Monte Verita`meeting on preferential flow processes and summarize the 2006 presentations, some of which are published in this issue of the Journal. New technologies and innovative experiments have increased our understanding of the conditions that initiate and sustain preferential flows. We identify contemporary exigencies, and suggest avenues for their resolution. We are progressing through observation-led discovery. Our prognosis is that new data will enable us to develop better models, and more aptly to parameterize existing models, and thereby predict the impact, benefits and detriments of preferential flow in soil.

A review of model applications for structured soils: a) Water flow and tracer transport

“…The latter is also treated in another recent review (Ma et al, 2007). Finally, the value of PF to ecosystem services was assessed with a global perspective by Clothier et al (2008).…”

Tracing shallow lateral preferential pathways of fluid movement using electrical geophysics

“…Rainfall events incorporate heterogenous saturation of soils due to vegetation cover, soil type, soil depth and rainfall intensity, overall soils would experience fluctuations in apparent conductivity due to water content (Clothier et al, 2007). Non-obvious channels represented as an LPP initially form on the soil surface as Figure depicts as a 'Major Flow path' following the fluctuations of topography; this is then attributed to the heterogeneities in soil saturation (Clothier et al, 2007, Melliger andNiemann, 2010).…”

“…It can be assumed that water flowing through a preferential pathway will saturate the soil leading to a higher conductivity relative to the surrounding soil profiles (Clothier et al, 2007). If this is the case, then electrical geophysics has the ability to measure and detect these anomalous zones uphill of an existing gully feature.…”

“…Local hydrological conditions will determine the nature of surface flows and groundwater movement including the infiltration depth, flow direction and rate of movement, although it is generally understood that water flows through physical or chemical channels known as preferential pathways (Clothier et al, 2007). Pathways develop within a medium due to the heterogeneities in the physical properties of the material that the water is flowing through.…”

Soil micromorphology use for modeling of a non-equilibrium water and solute movement

“…To describe such non-equilibrium of water flow and solute transport in soils, many numerical models have been recently developed. Overviews of non-equilibrium water flow and solute transport evidence, and various experimental and mathematical approaches to study and describe these phenomena were given by Šimůnek et al (2003), Gerke (2006), Jarvis (2007), Clothier et al (2008), Šimůnek et al (2008a), Šimůnek and van Genuchten (2008), or Köhne et al (2009a, b). Common physically based models for simulation of water flow and solute transport in structured soils assume (one) continuum and bi-or multi-continuum approaches.…”