Origin and assessment of water repellency of a sandy South Australian soil

Abstract

The water repellency of a sandy lucerne pasture soil is critically dependent on aqueous extraction and subsequent drying procedures. Freeze-drying converts a very severely water-repellent soil into a readily wettable soil, but subsequent rewetting and oven-drying regenerates water repellency. These changes are ascribed to changes in the molecular conformation of the organic matter. Prolonged shaking detaches organic matter coatings from sand particles and so reduces repellency. Allowing for these effects, it is shown that a sequence of alcohol-benzene extraction, acid leaching, and NaOH extraction removes the major part of the water-repellent substances present.

Investigation into mechanisms leading to the development, spread and persistence of soil water repellency following contamination by crude oil

“…Alternatively, if development of soil water repellency is initiated by sorption of liquid-phase petroleum compounds, time may be required for water and vapour-phase petroleum compounds to evaporate and to allow re-organization of the less volatile petroleum compounds. There is evidence that removal of water can induce conformational changes in the outermost layer of drying organic material (Ma'Shum and Farmer 1985). These changes typically reduce the affinity of peat and humic substances for water.…”

Characterization of disaggregated nonwettable surface soils found at old crude oil spill sites

“…Why some naturally occurring substances can generate water repellency in certain soils and not in others, however, remains to be elucidated. Until Tschapek (1984) and Ma'Shum and Farmer (1985) produced evidence suggesting that the molecular orientation of organic matter coatings on soil particles may be determining whether soils will repel or absorb water, most researchers thought that soil water repellency was attributable solely to the presence of organic material of unusual composition. Currently, however, the theory that soil water repellency is caused by naturally occurring amphiphilic organic material that display conformational flexibility is slowly gaining wider acceptance (Ma'Shum and Farmer 1985;Ma'Shum et al 1988;Anderson et al 1995).…”

“…Until Tschapek (1984) and Ma'Shum and Farmer (1985) produced evidence suggesting that the molecular orientation of organic matter coatings on soil particles may be determining whether soils will repel or absorb water, most researchers thought that soil water repellency was attributable solely to the presence of organic material of unusual composition. Currently, however, the theory that soil water repellency is caused by naturally occurring amphiphilic organic material that display conformational flexibility is slowly gaining wider acceptance (Ma'Shum and Farmer 1985;Ma'Shum et al 1988;Anderson et al 1995). According to this theory, amphiphilic or surface-active organic molecules, such as humic, fulvic, and fatty acids, can impart water-repellent character to a soil when their hydrophilic ends are oriented towards soil particle surfaces and their hydrophobic ends extend towards the open pore space (Voronin and Vityazev 1979;Tschapek 1984;Grelewicz and Plichta 1985;Ma'Shum and Farmer 1985;Ma'Shum et al 1988;Wallis et al 1990).…”

“…Currently, however, the theory that soil water repellency is caused by naturally occurring amphiphilic organic material that display conformational flexibility is slowly gaining wider acceptance (Ma'Shum and Farmer 1985;Ma'Shum et al 1988;Anderson et al 1995). According to this theory, amphiphilic or surface-active organic molecules, such as humic, fulvic, and fatty acids, can impart water-repellent character to a soil when their hydrophilic ends are oriented towards soil particle surfaces and their hydrophobic ends extend towards the open pore space (Voronin and Vityazev 1979;Tschapek 1984;Grelewicz and Plichta 1985;Ma'Shum and Farmer 1985;Ma'Shum et al 1988;Wallis et al 1990). The reverse arrangement is thought to prevail in soils that absorb water normally; that is, hydrophilic functional groups interact mostly with the soil solution whereas hydrophobic functional groups interact mostly with themselves and with the surface of organic matter coatings.…”

“…The reverse arrangement is thought to prevail in soils that absorb water normally; that is, hydrophilic functional groups interact mostly with the soil solution whereas hydrophobic functional groups interact mostly with themselves and with the surface of organic matter coatings. Changes in the interfacial conformation of amphiphilic organic molecules on the surface of soil particles has been postulated to occur during soil drying and following soil treatment with certain nonpolar organic solvents (Tschapek 1984;Ma'Shum and Farmer 1985;Ma'Shum et al 1988).…”