Towards more sustainable brine extraction in salt flats: Learning from the Salar de Atacama

摘要

Salt flats are hydrogeological systems with highly valuable wetland and lake ecosystems. The brine pumping carried out to extract lithium is modifying the natural evaporation discharge of salt flats. A methodology to evaluate the impacts caused on water table and evaporation discharge by brine exploitation in salt flats is proposed and applied to the Salar de Atacama. The methodology included field measurements of water table and evaporation rate, followed by its spatio-temporal analysis and the application of the results to a numerical model to improve the brine exploitation design. The spatio-temporal analysis of the water table depth and evaporation rates measured in the field concluded that the evaporation discharge decreased from 12.85 to 10.95 m~3-s~(-1) between 1986 and 2018, that is around 15%. This reduction compensated part of the extractions and could contribute to the preservation of the mixing zone ecosystems. At present, this damping capacity is already amortized in the nucleus and the marginal zone is beginning to be affected by the brine pumping. The sensitivity of the phreatic evaporation on the water table depth justified the great uncertainty of the previous evaporation discharge estimations. Thus, an average error lower than 0.5 m was enough to modify the evaporation by >60%. Therefore, considerable effort should invested to faithfully quantify the discharge by evaporation which is critical in water balance of salt flat basins. The numerical model pointed out that the total pumping outflow should be distributed in the largest possible area. This minimizes the water table drawdown and maximizes the capacity of the evaporation decline to compensate the extractions. The results of this work serve as guidelines to improve the efficiency of future salt flat exploitations.