The influence of surface crust dynamics and sediment availability on aeolian dust emission from ephemeral lake beds: Evidence from Etosha Pan, Namibia

Ephemeral lake beds (playas) are major global sources of atmospheric mineral dust, yet controls governing sediment availability and emission potential at fine spatial scales remain poorly constrained. This study presents the first in situ measurements of surface erodibility and potential PM₁₀ emission fluxes from Etosha Pan, Namibia. Threshold shear velocities and PM₁₀ emission fluxes were quantified using a Portable In-Situ Wind ERosion Laboratory (PI-SWERL) across five surface types spanning highly emissive hotspots to non-emissive consolidated salt crusts. Threshold shear velocities ranged from 0.38 m s⁻¹ on deflated clay-rich surfaces to >1.14 m s⁻¹ on recently inundated or cemented salt crusts, and PM₁₀ fluxes at u_⁎ = 0.56 m s⁻¹ varied by more than three orders of magnitude. Emissions were highest where degraded efflorescent crusts exposed fine sediment, whereas halite-rich crusts exhibited greater mechanical strength and resisted wind erosion despite low surface moisture. X-ray diffraction analyses confirmed spatial variability in evaporite and silicate mineral assemblages, with halite abundance inversely related to dust emission potential. Antecedent hydrological conditions regulated sediment availability. Moderate wetting–drying cycles promoted weak, emissive crusts, whilst persistently wet or dry conditions were associated with continuous, resistant crusts and reduced emissions. Distinct emission regimes arose from differences in crust failure and saltation feedbacks, highlighting sub-landform-scale variability in dust sources. Crust dynamism, driven by spatial variability in surface conditions and antecedent hydrological regime, is identified as a key, under-represented control on dust emission. The relationships quantified here provide new empirical constraints for improving the representation of sediment availability in global dust modelling.