Open AccessHydrogeologic and Geochemical Distinctions in Freshwater‐Brine Systems of an Andean Salar
Author(s) -
Munk L. A.,
Boutt D. F.,
Moran B. J.,
McKnight S. V.,
Jenckes J.
Publication year - 2021
Publication title -
geochemistry, geophysics, geosystems
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.928
H-Index - 136
ISSN - 1525-2027
DOI - 10.1029/2020gc009345
Subject(s) - halite , geology , hydrogeology , groundwater , calcite , aquifer , hydrology (agriculture) , arid , geochemistry , surface water , water table , wadi , evaporite , transition zone , gypsum , sedimentary rock , environmental science , paleontology , geotechnical engineering , cartography , environmental engineering , geography
The Salar de Atacama contains one of the world's most important lithium resources and hosts unique and fragile desert ecosystems. Water use issues of the hyper‐arid region have placed it at the center of global attention. This work combines geochemical and hydrogeologic data with remote sensing analysis to address differences in water zones in the marginal environments of the salar. Water samples from across the inflow to brine transition were collected over the period 2012–2016 and analyzed for ẟD, 3 H, 87 Sr/ 86 Sr and major and minor elements. The ẟD values range from about −64‰ to +20‰, 3 H as R mod from 0.01 to 0.36 and the 87 Sr/ 86 Sr from 0.70750 to 0.70804 with highest ẟD and 3 H occurring in the regions of open water. Geochemical modeling results indicate inflow and shallow transition zone waters are saturated with respect to calcite, whereas all others are saturated with respect to calcite, gypsum, and halite. Long‐term remote‐sensing of surface water body extents indicate that extreme precipitation events are the primary driver of surface area changes as exemplified by an increase in size of the lagoons by a factor of 2.7 after a storm. A new conceptual model of the freshwater to brine transition zone that incorporates variability in aquifer geology, hydrology and geochemistry to explain important marginal water bodies is presented. The subsurface brines in the transition zone and the halite nucleus are geochemically distinct compared to the groundwater discharge features (e.g., lagoons) over modern time scales which aids in conceptualizing the transition zone system.