Baseline Water Quality and Geochemical Factors that Control Shallow Groundwater used by Indigenous Communities in the Vicinity of the Salar de Uyuni, Bolivia

Abstract

One of the largest known global lithium brine resources is the Salar de Uyuni (SDU) in the Bolivian Altiplano, yet presently, lithium exploitation is limited. Large-scale future lithium extraction could impact the regional water resources, which are used by local indigenous communities living in the vicinity of the SDU. Here, we investigate the water quality and geochemistry of shallow groundwater in the watershed of the SDU, aiming to evaluate the geochemical factors that control the occurrence of geogenic contaminants. We present a suite of geochemical and strontium isotopic analyses of shallow groundwaters and some surface waters (n=63) used by communities surrounding the SDU. Integrated water quality data shows that most of the groundwater samples exceeded the World Health Organization (WHO) drinking water standards for at least one contaminant. We show that salinity, arsenic, boron and lithium are the major geogenic constituents that pose risks to human health and are consistent with the established patterns of geogenic water quality issues reported for other water resources in the high Andes. Our geochemical analysis reveals that the local lithology directly controls the geochemistry and water quality in which low salinity groundwater associated with andesitic volcanic rocks in the western areas of the SDU is associated with distinctively high boron, B/Li, Mg/Li, and low Sr isotope ratios relative to groundwater from the eastern side with a wider range of chemical compositions and high Sr isotope ratios, reflecting the role of low-temperature water-rock interactions. Conversely, saline groundwater with low B/Li and Mg/Li ratios indicate mixing with underlying geothermal waters. Future large-scale lithium extraction could likely cause regional groundwater level drawdown and thus further increase the impact of underlying saline geothermal waters, exacerbating the already impaired quality of water resources available for the local indigenous communities.