Cyanobacterial soil crust responses to rainfall and effects on wind erosion in a semiarid environment, Australia: implications for landscape stability

Cyanobacterial biocrusts (CBCs) perform a range of functions including early successional colonization of substrates, modification of soil properties, surface stabilization and carbon sequestration. The response of CBCs to hydration is well-constrained for cultured or single-species but less so for in situ communities and there are few studies of CBC response to, and impact on, wind erosion. This paper investigates the in situ response of dryland CBCs to rainfall and wind erosion using biological and physical indicators. Field sites are in central Australia in three geomorphic situations - sand dune, nebkha and claypan. Results indicate higher amounts of rainfall trigger a more intense biological response than lower amounts, but not one of longer duration. The intensity of photosynthetic response to rainfall appears related to air temperature. The relationship between CBC and soil loss by wind erosion is inconclusive, but saltation efficiency (Qs/Q) is highest on the dune and claypan when tested 48 hr after applying 5 mm of rainfall. This is attributed to rainfall detachment of sand particles increasing the availability of loose erodible material on the surface. The results highlight the rapid biological response of CBCs to rainfall events (within hours), and the importance of overall environmental conditions, such as air temperature, but raise questions as to the longevity of the biological impact of such response. Drought-affected CBCs can protect the surface against wind erosion but dehydration may reduce resilience to disturbance and, under predicted future climate scenarios, the protective role of cyanobacterial crusts may be compromised.

Plain Language Summary

Biological crusts comprise one or more of cyanobacteria, fungi, algae, lichen and mosses. They are tolerant to high temperatures and long periods of drought and can bind soil particles together making them less susceptible to erosion. This paper examines how cyanobacteria-dominated soil crusts respond to rainfall and whether that response affects the likelihood of wind erosion. We used a rainfall simulator and a wind tunnel and conducted experiments on a sand dune, the area between the dune and a floodplain, and the floodplain itself. We examined changes in the biological and physical characteristics of the cyanobacterial crust for no rain, 5 mm rain and 10 mm rain. Higher amounts of rainfall led to more biological change than lower amounts. The wind is most effective following 5 mm rain probably because the rain causes sand particles to come to the surface and when the wind blows these particles they impact other particles causing erosion. Cyanobacterial crusts react quickly to rainfall but the response does not last long (less than a day). Drought affected cyanobacterial crusts can protect the surface against wind erosion but this ability may be reduced if future climate conditions are warmer with longer periods between rain.