A qualitative study of recharge in the southern part of the Salar de Atacama has been made based on hydrogeochemical and isotopic techniques. Precipitation water samples correspond to the accumulated rainfall in the period 2017-2019. The local meteoric line of precipitation is established from the values of δ18O and δ2H in rainwater of the southern part of the Salar de Atacama, complemented with data from snow samples obtained in June 2017 in the Salar itself. The equation of the local meteoric line is approximately δ2H = 8δ18O + 15 ‰ V-SMOW.
Several field observations in the upper parts of the southeastern basins contributing to the Salar de Atacama show that a large part of their surface is covered by ignimbrite deposits and alluvial and aeolian sediments associated with the weathering of these volcanic rocks. The capacity of ignimbrites to allow significant diffuse recharge is at most very small because a large part of the rainwater that falls on their surface is stored, increasing soil humidity, and is subjected to intense evapotranspiration. Also, the thickness of the alluvial and wind deposits existing in these areas suggests that the field capacity must be quite significant, so recharge process through the soil would be very limited.
The isotopic composition of the water in some lagoons at the boundary with the large salt flat (salar) is particularly interesting when making the isotopic interpretation of δ18O and δ2H to evaluate the recharge. Ephemeral lagoons accumulate water from surface runoff of large sectors of the upper part of the Salar de Atacama southeastern area, where it slowly infiltrates and recharges the aquifer. The isotope composition of water of these lagoons shows isotopic fractionation by evaporation and reaches values that respond quite well with the isotopic composition of groundwater throughout the eastern edge of the Salar de Atacama. This would indicate that the recharge at the eastern edge of the Salar de Atacama is a preferential process, as it happens in many other arid areas of the planet. Thus, it is possible that the recharge that occurs at the southeastern edge of the Salar is only preferential and occurs when important precipitation events are produced, which are capable of generating significant runoff that is temporarily stored in the lagoons.