Particle size distributions of South Tunisian soils erodible by wind

Abstract

180 samples representative of surface soils erodible by wind were collected in South Tunisia to retrieve their grain size distribution. Dry sieving using 13 sieves was favour to preserve as much as possible the soil aggregates in their natural state. Two different methods were used to characterize the grain size distribution; the φ method of moments and the use of a combination of log-normal statistical functions. Both methods underline the ubiquitous and dominant presence of a very fne sand population (around 100 μm in diameter), very well sorted (σm=1,23) which corresponds to the grain size range for which the wind energy required for initiating the aeolian erosion is minimum. This clearly suggests that most of the soils in South Tunisia have the potential to be easily eroded by wind. However, in about 1/3 of the samples mainly those located in Dahars and in the vicinity of mountains, a secondary population of coarse grains (1500 μm in diameter) is also observed. This coarse mode could signifcantly reduce the wind erosion of the soils where it is present by covering a part of the surface and by limiting the effciency of the wind transfer to the surface. © 2011 Lavoisier. All rights reserved.