THE ROLE OF EFFLORESCENT SULFATE SALTS IN DUST PRODUCTION AT WHITE SANDS NATIONAL PARK, NEW MEXICO

The White Sands eolian system in the northern Chihuahuan Desert of New Mexico, USA is a hot spot of dust emissions. Dust is sourced from eolian abrasion of gypsum dune sand and from wind erosion of playa sediments from Alkali Flat and Lake Lucero located upwind of the dune field, from where it is episodically transported hundreds of kilometers downwind. Dust emission processes on the playa include saltation bombardment of sand that liberates dust from fine-grained playa sediment, the breakdown of saltating sand-sized salt-silt-clay aggregates, and the direct aerodynamic entrainment of dust. These processes may vary seasonally with changing surface and groundwater conditions. Alkali Flat and Lake Lucero are wet playa systems with shallow groundwater where evaporation leads to the widespread precipitation of evaporite minerals. Mirabilite (NaSO₄·10H₂O) and thenardite (NaSO₄) salts undergo phase and volume changes with fluctuations in temperature and relative humidity, forming loose, fluffy surface sediment that is easily eroded by the wind. PI-SWERL tests reveal that thenardite salts produce some of the highest dust fluxes in the White Sands eolian system (~60 mg/m²/s) compared with typical playa and dune fluxes (1-2 mg/m²/s). Preliminary compositional data from dust at the downwind White Mountain IMPROVE site indicates an increase in sodium, calcium, and sulfate in cold season dust emissions, suggesting both sulfate salts and gypsum may dominate dust composition in the spring. Daily to seasonal changes in moisture, temperature, and wind set the stage for cold season dust storms likely dominated by sulfate salts, whereas spring and summer dust storms are likely derived from gypsum sand abrasion and erosion of playa sediments. Sulfate salts are replenished during winter and spring on the playa surface following wind erosion or precipitation events due to a relatively high water table. A reduction in salt precipitation occurs in summer as the water table drops. Sulfate salts including thenardite are a known component of wind-eroding playas around the world and are a potentially under-attributed dust source based on the seasonal moisture regime of playas.