Hydrodynamics of salt flat basins: The Salar de Atacama example

Abstract

The Salar de Atacama is one of the most well-known saline endorheic basins in the world. It accumulates the world main lithium reserves and contains very sensitive ecosystems. The objective of this work is to characterize the hydrodynamics of the Salar de Atacama, and to quantify its complex water balance prior to the intense brine extraction. The methodology and results can be extrapolated to the groundwater flow and recharge of other salt flats. A three-dimensional groundwater flow model using low computational effort was calibrated against hundreds of hydraulic head measurements. The water infiltrated from the mountains ascends as a vertical flux through the saline interface (mixing zone) produced by the density contrast between the recharged freshwater and the evaporated brine of the salt flat nucleus. This water discharges and is largely evaporated from lakes or directly from the shallow water table. On the other hand, the very low hydraulic gradients, coupled with the presence of the mixing zone that operates as barrier, leads the salt flat nucleus to act as a hydrodynamically quasi-isolated area. The computed water table shows the lowest hydraulic head in the salt flat nucleus near the discharge at the mixing zone. The groundwater balance of the Salar de Atacama in its natural regime was quantified resulting in an inflow/outflow of 14.9 m·s. This balance considers the basin as an endorheic system. The very low infiltration values that are generally assumed for hyperarid basins are not consistent with the hydrogeology of the Salar de Atacama. Indeed, very high infiltration rates (up to 85% of rainfall) occur because of the high degree of fracturing of rocks and the scarce vegetation. This high infiltration is consistent with the light isotopic composition of the water from the recharge area (Altiplano). Therefore, the existence of additional inflows outside the basin is unlikely.

Residence time distributions in non-uniform aquifer recharge and thickness conditions – An analytical approach based on the assumption of Dupuit-Forchheimer

“…If the mountainous block is sufficiently permeable, an aquifer with decreasing thickness downstream -following the geometry of the orogen -may eventually form (Mountain Block of Figure 7), e.g. the Salar de Atacama basin (Marazuela et al, 2019). On the other hand, if the mountainous block is not permeable enough, the effective precipitation is mainly converted into runoff.…”

Indigenous peoples’ rights to natural resources in Argentina: the challenges of impact assessment, consent and fair and equitable benefit-sharing in cases of lithium mining

“…In particular, water is a central resource of concernthe ecosystem in the area, which is 4300 metres above sea level and reliant on a closed water basin, is fragile. A main concern among communities about mining projects thus relates to the possible contamination of their fresh water supplies, due to the amount of water used in lithium extraction, and possible mixing between fresh and saltwater systems within the basins (Marazuela et al 2018). However, the communities in the area are also in desperate need of employment and, often, basic services, making investments in economic ventures in the area attractive.…”

Genetic studies of various Prosopis species (Leguminosae, Section Algarobia) co‐occurring in oases of the Atacama Desert (northern Chile)

“…This basin was used as a natural and cultural corridor since pre‐Columbian times (Marquet et al., 1998; Núñez, 1971), passing beyond different vegetation belts, although riparian plants predominate along the watercourse (Gajardo, 1994; Villagrán & Castro, 2004). Finally, the Salar de Atacama is an endorheic basin within the Prepuna foothills (Arriagada et al., 2006; Marazuela et al., 2019). Different quebradas flow into this system giving rise to several oases with riparian vegetation (Gajardo, 1994; Villagrán & Castro, 2004).…”