Effects of Salt Mineralogy on Dust Emissions, Salton Sea, California

Abstract

Some of the most emissive surfaces on Earth are dominated by salt minerals. We hypothesized that the vulnerability of surfaces to eolian erosion may be controlled by salt mineralogy and crystal habit. We used x-ray diffractometry (XRD) and scanning electron microscopy–energy dispersive x-ray spectrometry (SEM-EDS) analyses to measure salt mineral assemblages and crystal habits along exposed shorelines of the Salton Sea, California. Potential dust emissions were also measured using the Portable In-Situ Wind Erosion Lab (PI-SWERL). Results indicate that surfaces with the highest emissions, up to ∼1 mg m−2 s−1, are composed of hydrous/anhydrous salt minerals and minerals with acicular or prismatic crystal habits. Hydrous/anhydrous minerals (mirabilite/thenardite, eugsterite/glauberite, gypsum/bassanite, and numerous Mg sulfates) are more unstable under changing environmental conditions, are likely to dissolve and reprecipitate repeatedly, form less cohesive tiny individual crystals or small aggregates, and are therefore more likely to result in highly emissive surfaces. Salt minerals with acicular or prismatic habits are more likely to be disruptive, enhance salt heave, lessen the degree of interlocking precipitates, and form loose, "puffy" crusts that are highly emissive. Low-sloping surfaces near the shoreline had greater fluctuations in water content and relative humidity, triggering frequent salt mineral dissolution–precipitation and increased emissions. A high water table also allowed a continuously replenishing supply of salt crystals, increasing the potential for extensive dust emissions. Surfaces containing salt minerals are incredibly dynamic, but understanding the processes that control surface characteristics is an important step in mitigating dust emissions.