Effects of Salt Mineralogy on Surface Characteristics: Implications for Dust Emissions, Salton Sea California, USA

Salt minerals in soils can exert a profound influence on both the amount of fine material available for eolian erosion and the spatial and temporal distribution of dust emissions. The degree of susceptibility of these surfaces to eolian erosion may be partly controlled by the salt mineralogy. We hypothesize that salt mineralogy and crystal habit affect dust emissions. To test this, we used XRD and SEM/EDS analyses to measure the salt mineral assemblages, crystal habits, and other surficial characteristics of numerous sites along recently exposed shorelines of the Salton Sea. These data were compared to potential dust emissions measured using the Portable In-Situ Wind Erosion Lab. The surfaces with the highest emissions have the following in common: the presence of hydrating salt minerals, loosely cemented (non-interlocking) salt crystals or aggregates, acicular or prismatic crystal habits and a low slope. Salt crusts composed of hydrating minerals, mirabilite/thenardite; eugsterite/glauberite; gypsum/bassanite; and/or numerous Mg-sulfates, are more likely to dissolve and re-precipitate repeatedly (i.e. diurnally, seasonally), form tiny individual crystals or small aggregates, and be less cohesive and more likely to result in highly emissive surfaces. Additionally, 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 water contents decrease cohesion among particles and increase dust emissions. Low-sloping surfaces with shallow water tables near the shoreline have greater fluctuations in water content and relative humidity, which can lead to frequent salt mineral dissolution/precipitation (diurnally or even more frequent). Additionally, the high water table allows for a continuously replenishing supply of salt crystals, increasing the potential for extensive dust emissions. Therefore, salt mineral dynamics in these systems is a primary controller of surface characteristics and dust emissions.