ARS | Publication request: On water repellency, humidity, fire, and wind erosion in arid landscapes

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: December 14, 2006
Publication Date: May 2, 2007
Citation: Over, T.M., Ravi, S., D'Odorico, P.D., Zobeck, T.M., Herbert, B. 2007. On water repellency, humidity, fire, and wind erosion in arid landscapes [abstract]. Bouyoucos Conference April 29-May 3, 2007, Sanibel Island, Florida.

Technical Abstract: Studies of water repellent soils have usually focused on their effect on infiltration and runoff. In arid regions, however, the landscape is often shaped more by wind than by water, with important implications for ecology and land management. In a series of field, laboratory, and theoretical experiments, we have explored the effects of hydrophobic compounds (naturally occurring because of fire and artificially applied) and variations in atmospheric humidity on erodibility by wind (measured in a wind tunnel), on soil-water relations including equilibrium soil-water content and the soil moisture retention curve, and on inter-particle bonding forces in arid land soils from the southwestern US and in clean sand. The wind tunnel experiments show a consistent and significant increase in erodibility by wind in soils made hydrophobic by fire in both grass- and shrub-lands, and in clean sand made hydrophobic by treatment with palmitic acid. The effect of atmospheric humidity on erodibility is less significant, but drier conditions indicate greater erodibility regardless of water repellency. These results are partially explained by theoretical calculations showing a decrease in inter-particle bonding forces due to capillarity at larger contact angles. Equilibrium soil-water content increased with atmospheric humidity as expected, but differed insignificantly between naturally or artificially hydrophobic soils and their unburned or untreated versions. The soil moisture retention curves so far have given inconsistent results: in the air-dry range, the palmitic acid – treated sand had a lower suction for a given water content compared to the untreated sand, while a burned grassland soil had a greater suction compared to the more hydrophilic unburned version of the same soil.