Cycling of Gypsiferous White Sands Aerosols in the Shallow Critical Zone at White Mountain, New Mexico
Dry deposition significantly affects evolution of the critical zone by nutrient supply and contributing to soil genesis. Dust influx and cycling in soils are difficult to quantify because dust sources can be chemically similar to local soils. White Sands, New Mexico, emits gypsum dust with a unique chemical and isotopic signature, providing an opportunity to investigate dust deposition and its movement in soils. This study evaluated the mobility of White Sands dust particles in the critical zone at White Mountain, New Mexico, a highland 100 km downwind. Four soil profiles were collected over limestone, igneous, mixed limestone and dolostone, and sandstone bedrocks, as well as leaves of local grass, shrubs, cacti, and pines. Dust, White Sands gypsum, and bedrock, considered as end members of soil calcium, were collected. All samples were analyzed chemically, mineralogically, and isotopically ( 87Sr/86Sr). Depth variation in bulk soil chemistry at the study sites was mostly controlled by weathering over carbonate substrates, and by bulk dust addition over siliciclastic ones. White Sands, making up only a small portion of soil mass, dominantly controlled the Ca/Sr ratios, SO4 concentrations, and 87Sr/86Sr ratios in water leachable fractions of the soils. Dust samples contained more soluble Ca and SO4 than soils, suggesting high mobility of these soluble ions. For water-leachable fraction of the soils, Ca concentrations and the Sr/Ca ratio increased with depth as gypsum dissolved and reprecipitated as it reaches the impermeable bedrock-soil interface. The residence time of White Sands-derived gypsum in soil profiles was estimated to be approximately 66 years for Ca, and 83 years for SO4. The 87Sr/86Sr ratios in plants varied among plant types, primarily controlled by root depth, and dominantly sourced from dust. Although variation in Ca and Sr concentrations within the plants were largely controlled by plant type, concentrations of other elements were likely controlled by other variables such as vegetation cover and geomorphology. Overall, tracking White Sands dust input to the soil has provided better understanding of gypsum's potential effects and the effects of long-distance dust transport on critical zone dynamics and sources of bioavailable plant nutrients.
Rea, Patrick, "Cycling of Gypsiferous White Sands Aerosols in the Shallow Critical Zone at White Mountain, New Mexico" (2017). ETD Collection for University of Texas, El Paso. AAI10688640.