A wind tunnel study of the resilience of three fungal crusts to particle abrasion during aeolian sediment transport

This study is a comparison of the strength, stability and resistance to abrasion of monospecific sand crusts formed by three species of free-living fungi: Aureobasidium pullulans, Trichoderma harzianum, and Absidia corymbifera. Compared to three photoautotrophs examined in a previous study, the fungal crusts were thicker and stronger in flexure by a factor of two or more. In addition to the morphological properties of these fungi, the organic substrate required for growth contributes to the total crust strength. Wind tunnel tests, in which the crusts were subjected to particle impact from an upwind sediment source (nominally 0.014 kg m−1 s−1) and varied levels of freestream velocity (u∞), showed that crusts comprised of Trichoderma and Absidia were stable at wind velocities under 10 m s−1. Crusts of Aureobasidium generally ruptured at velocities well below this level and to a much greater extent. The distinctive morphologies and metabolic rates of the three fungi appear to explain these differences. As compared to the wind tunnel experiments, independent tests of crust strength in flexure, which were intended to simulate crust flaking, were found to be less sensitive indicators of relative crust stability in aeolian settings. Analysis of the time rate of expansion of the perimeter of crust loss indicates that this relation is approximately exponential, with the exception of low wind velocities near the threshold for grain ejection where the momentum of the saltators at impact appears to be of prime importance.