Wind Erosion in Western Queensland Australia

Chapter 2 – Land Erodibility Controls(above threshold) is once again exposed. This has implications for modelling the effects ofsoil moisture on wind erosion rates, as changes to the moisture content in the topmostexposed surface particles may occur (moving to an erodible state) that are not detectable bymost measurement or modelling approaches.A number of the moisture models have been implemented in wind erosion models, includingin EPIC (Chepil, 1956), AEOLUS II (Belly, 1964), TEAM (Gregory and Darwish, 1990),WEPS (Saleh and Fryrear, 1995), DPM (Fécan et al., 1999), and WEAM and IWEMS (Shaoet al., 1996). While gravimetric moisture content can easily be measured in the field, and hasbeen used in the early empirical regression functions, the use of volumetric moisture contentin later models reflects developments in integrated modelling approaches that couple winderosion prediction systems with models of land surface and soil conditions (Shao, 2000).2.2.6 Surface Crusting and DisturbanceCrust Types, Formation and BreakdownSurface crusts form as a result of the binding of soil particles at or near the soil surface. Soilsurface crusting may be driven by physical processes or biological activity. Both physical andbiological crusts play an important role in controlling soil erodibility.Two main types of physical crust exist. These are identified by their mechanisms offormation. The first, structural crusts, form as a result of water droplet impact (e.g. duringrainfall) and in situ particle rearrangement. The second, depositional crusts, form bydeposition of fine particles transported from some source (Valentin and Bresson, 1992). Bothstructural and depositional crusts are associated with a number of sub-types that reflect morespecific processes during formation. Sub-types of structural crusts include: slaking, infilling,coalescing and sieving crusts. Each of these is characterized by a specific lateral structureresulting from the factors driving formation. Sub-types of depositional crusts include: runoffdepositional crusts, still depositional crusts, and erosion crusts (Valentin and Bresson, 1992).The formation of a particular crust type is dependent on the characteristics of precipitation(i.e. amount, frequency and intensity), soil texture, and local topography. Soil chemistry, forexample CaCO 3 and salt content, and organic matter content have also been identified as keydeterminants in physical crust formation (Gillette et al., 1980, 1982).50