NOBLE GAS STABLE ISOTOPE RECONSTRUCTION OF BACKGROUND CLIMATOLOGICAL WATER TABLE DEPTHS: AN INDICATOR OF LITHIUM MINING IMPACTS

The Lithium Triangle at the intersection of Chile, Argentina, and Bolivia contains more than half of the world’s lithium reserves.¹ While lithium has been mined here for decades, production has increased exponentially in recent years with the expanding market for lithium batteries—the storage power behind personal electronics and electric vehicles. Local communities are concerned about socio-environmental impacts of lithium mining, as the extraction process involves pumping and evaporating large volumes of mineral-rich groundwater. Groundwater is a non-renewable resource² in this hyper-arid region and the foundation of both the desert ecosystem and local Indigenous cosmology.

We apply a recently developed tool to reconstruct past water table depths using the isotopic composition of noble gases dissolved in groundwater in the Salar de Atacama, Chile, and Salinas Grandes, Argentina. Gravitational settling in the unsaturated zone of soils causes the heavy-to-light ratio of xenon and krypton isotopes to increase linearly with depth.³ Gases dissolved in groundwater thus reflect the depth-dependent isotopic composition of the unsaturated zone air just above the water table, recording the signal of the water table depth.

This project has been developed in collaboration with local indigenous communities with the goal of evaluating conflicting hydrological models^4,5 of basins in the Lithium Triangle and ultimately assessing potential lithium mining impacts to groundwater.

1) 4. Kay (2018) Investing News. 2) Corenthal, et al. (2016) Geophys. Res. Lett. 43. 3) Seltzer, et al. (2017) Water Resources Research 53: 2716-2732. 4) Boutt et al. (2016) Hydrological Processes 30: 4720-4740. 5) Marazuela et al. (2019) Science of the Total Environment 654: 1118-1131.