Rain, wind and crusts: small scale processes drive landscape erodibility
1, Helene Aubault2, Joanna Bullard2, Hossein Ghadiri3, Grant McTainsh3
1Australian National University, Canberra, ACT, Australia, 2Loughborough Univeristy, Loughborough, UK, 3Griffith University, Brisbane, QLD, Australia
Arid and semi-arid areas are subject to extreme hydrological regimes with long periods of drought characterised high susceptibility of soils to wind erosion, and periods of heavy rainfall or flooding characterised by saturated soils and water erosion. Moisture variability significantly changes the composition of soil surface crusts (mixture of cyanobacterial and physical crusts) thereby impacting the soil surface erodibility. Although there is a relatively good understanding of the interactions between rainfall, crust development and impacts on soil erodibility in a laboratory environment, there is still a need for better in-field understanding of these processes.
This study quantifies the interaction between soil surface crusts, rainfall, and wind erosion processes in field. It aims to understand the role of rainfall on the ability of cyanobacterial soil crusts to stabilise surfaces. Heavy rainfall events (15 and 25 mm) were applied with a rainfall simulator across different crusts (mixtures of cyanobacterial and physical) typically found in arid floodplains. A micro wind tunnel was used to quantify changes in soil erodibility post rainfall.
The results highlight 1. The surfaces of physical crusts were more susceptible to raindrop impact, changing the surface microtopography, but this did not result in higher wind erosion rates compared to biological crusts. 2. Biological crusts in general had higher sediment losses induced by wind erosion, attributed to greater surface roughness and storage of loose erodible material. 3. The timing and quantity of rainfall was an important influence on soil erodibility and this varied between different cyanobacterial crust types.
While the differences between physical and cyanobacteria crusts at an experimental plot scale can be quantified and conclusions about the relative erodibility of each, this study reinforces the complexity of soil erodibility drivers at a landscape scale. The response of one crust type to rainfall or saltation will impact the neighbouring crust type. Given the predicted changes in rainfall frequency, intensity and patterns, the dominance of different cyanobacterial crust may very well alter the currently perceived wind erodibilty of arid lands.