Wind Erosion in Western Queensland Australia

Chapter 4 –Modelling Soil Erodibility DynamicsMarticorena and Bergametti, 1995; Lu and Shao, 2001; Hagen, 2004). Modelling soilerodibility terms of Q instead of u *t limits integration of the framework into existing winderosion models. Furthermore, soil erodibility predictions based on Q exist relative to areference wind velocity (e.g. 65 kmh -1 ) at which the wind tunnel experiments were conductedto obtain the model expressions (Equations 4.2, 4.3 and 4.6). This means that at higher orlower wind velocities the model may under- or over-predict soil erodibility.Limitation 2. The model does not consider soil moisture effects on soil erodibility. Anextensive body of research has been published on soil moisture effects on wind erosion(Cornelis and Gabriels, 2003). This research has considered soil moisture effects in terms ofits influence on u *t . Modelling soil erodibility in terms of soil crust and aggregate conditions,and separate from soil moisture, is legitimate when the soil moisture content is below thethreshold water content that may induce an increase in u *t , and therefore decrease inerodibility (Fécan et al., 1999). The model will fail in situations where the soil moisturecontent is above this threshold. Under these conditions Q min will not be defined by Equation(4.6), but will be equal to zero. Integrating a factor to account for soil moisture effects on soilerodibility is feasible and could be achieved by adjusting the output by a ratio of erodibilityunder moist soil conditions to that under dry soil conditions.Limitation 3. The model does not specifically account for the effects of biological soil crustson soil erodibility. The responses of physical and biological crusts to rainfall and disturbancemay vary significantly depending on antecedent conditions and disturbance types. Belnap andGillette (1998) reported that disturbance to physical soil crusts can have a greater effect onincreasing erodibility than disturbance of biological crusts due to a lower capacity to retainaggregation. Accounting for these effects under the model framework is beyond the scope ofcurrent research. In a spatial modelling context this may be addressed by incorporatingfactors to account for the likely distribution of biological crusts (e.g. Bowker et al., 2006) anddifferential rates of change in aggregation.Limitation 4. The model considers only rainfall effects, and not freeze-thaw process effectson soil aggregate breakdown. While the focus of this paper has been to present a frameworkfor modelling soil erodibility dynamics in hot, dry rangeland environments, the effects offreeze-thaw processes must not be ignored. The effects of freeze-thaw cycles on soilerodibility could be considered by the addition of a temperature component to the model120