CYCLING OF GYPSIFEROUS WHITE SANDS AEROSOLS IN SHALLOW CRITICAL ZONE SOILS AT WHITE MOUNTAIN, NEW MEXICO

Dry deposition impacts evolution of the critical zone through nutrient supply and contributing to soil genesis. Dust influx and cycling in soils is difficult to quantify because dust sources can be chemically similar to local soils. White Sands, New Mexico, emits gypsum dust with unique geochemical signatures, providing an opportunity to investigate its deposition and movement in soils. This study aims to understand transport and mobility of White Sands dust in the critical zone at White Mountain, New Mexico, a highland ~100km downwind. Four soil profiles were collected over limestone, igneous, dolostone, and sandstone bedrocks, as well as leaves of local grasses, 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 sites is controlled mostly by weathering over carbonate substrates and bulk dust addition over siliciclastic ones. White Sands gypsum, making up only a small portion of soil mass, was identified through Sr/Ca ratios, SO₄ concentrations, and ⁸⁷Sr/⁸⁶Sr in water leachable fractions. Dust samples contain significantly more soluble Ca and SO₄ than soils, indicating that gypsum dust deposition, while significant, is lost quickly through chemical reactions. Water leachable concentrations and Sr/Ca ratio increase with depth as gypsum dissolves and reprecipitates. Leachate Ca: SO₄ ratios decrease with depth as soluble Ca is adsorbed to clay. Plant Sr/Ca varies between sites and species.

Bulk soil ⁸⁷Sr/⁸⁶Sr is controlled by total dust input in the upper profile and bedrock weathering at depth. Gypsum does not modify such ⁸⁷Sr/⁸⁶Sr due to low mass. Plant ⁸⁷Sr/⁸⁶Sr varies between plant types, controlled by root depth, preferred source uptake, and variance in nutrient requirements. The ⁸⁷Sr/⁸⁶Sr and Sr/Ca of White Sands dust are being characterized and will be used to quantify relative contributions to the total soil Ca budget. Results from this study will characterize gypsum-derived Ca movement in shallow soils. Tracking White Sands dust input to the soil will give better understanding of gypsum’s potential effects on critical zone dynamics and biologic development.