Submitted to: Aeolian Research
Publication Type: Peer reviewed journal
Publication Acceptance Date: 3/9/2011
Publication Date: 6/1/2011
Citation: Baddock, M.C., Zobeck, T.M., Van Pelt, R.S., Fredrickson, E.L. 2011. Dust emissions from undisturbed and disturbed, crusted playa surfaces: cattle trampling effects. Aeolian Research. 3(1):31-41. Interpretive Summary: Dry lakes (playas) can be highly erodible locations and they commonly act as sources of dust in semi-arid environments. Their sediments have a high proportion of fine grains, but strong cohesion between the particles means the sediments can be consolidated into crusts which are resistant to wind erosion. These surfaces are termed supply-limited i.e. the capacity to produce dust is determined primarily by the availability of sediment, not the strength of the wind. Disturbance of these surfaces is a critical factor in making them emit dust. This study looked at the impact of cattle trampling on dust release from a playa in the northern Chihuahua Desert of New Mexico where there is considerable grazing. A portable wind tunnel was used to investigate the amount of dust produced after a single cow pass, and then after the heavier trampling of ten passes. For the particular playa studied, the effect of one cow pass was found to be insignificant, and did not generate more dust than the pristine playa surface under the same wind. This level of animal disturbance therefore did not enhance dust emission from the intact surface, even when it was bombarded by sand added to the flow of the wind tunnel, to simulate natural dust storms. 10 passes by a cow did result in appreciably more fine dust than the undisturbed playa surface. The increased emission caused by this level of disturbance was found to last for just over 30 minutes before the surface no longer showed the positive effect of the trampling. This research highlights the importance of crusts in protecting land surfaces from wind erosion. It also highlights the idea of ‘thresholds of disturbance’ which must be exceeded before enhanced wind erosion can be expected from a natural soil surface, following its disruption.
Technical Abstract: Dry playa lake beds can be significant sources of fine dust emission. This study used a portable field wind tunnel to quantify the PM10 emissions from a bare, fine-textured playa surface located in the far northern Chihuahua Desert. The natural, undisturbed crust and its subjection to two levels of animal disturbance (one and ten cow passes) were tested. The wind tunnel generated dust emissions under controlled conditions for firstly an initial blow-off of the surface, followed by two longer runs with sand added to the flow as an abrader material. Dust was measured using a GRIMM particle monitor. For the study playa, no significant differences in PM10 concentration and emission flux were found between the untrampled surface and following a single animal pass. This was the case for both the initial blow-offs and tests on plots under a steady abrader rate. Significantly higher dust loading was only associated with the effect of 10 animal passes. In the blow-offs, the higer PM10 yield after 10 passes reflected the greater availability of easily entrainable fine particles. Under abrasion, the effect of the heaviest trampling increased the emission flux by a third and abrasion efficiency by around 50% more than values on the untrampled surface. This enhanced abrasion efficiency peristed for a 30 minute period under abrasion before the positive effect of the disturbance was no longer evident. The findings highlight the role of a threshold of disturbance that determines if supply-limited surfaces will exhibit enhanced wind erosion or not after undergoing perturbation.