Hydrogeologic and Geochemical Distinctions in Freshwater‐Brine Systems of an Andean Salar

Abstract

The marginal environments of salar (e.g., salt flats) systems are unique ecological and hydrogeological regions of great importance in arid to hyper-arid climates (Pigati et al., 2014; Rosen, 1994; Warren, 2016). These distinctive places have become one of the most significant areas of concern in regions where groundwater and/or brine extraction are relied on for human use including resource development and fresh water sources used by communities (Houston et al., 2011; Tyler et al., 2006; Warren, 2010). As demand for water sources continues to increase (Gleeson et al., 2020; Wang et al., 2018; Zipper et al., 2020) it is critical to have a complete and scientifically based assessment of these transitional zone regions where freshwater discharges and evaporates above brackish and brine water in the subsurface. This process is what supports the formation of springs, wetlands or marshes (vegas), and lagoons (lagunas) that form important ecosystems on the margins of all salars on a global scale. However, the extent of development of these groundwater

Relic Groundwater and Prolonged Drought Confound Interpretations of Water Sustainability and Lithium Extraction in Arid Lands

“…The impacts from brine extraction cannot be equated to the impacts from fresh groundwater extraction. As shown here and in previous works (e.g., Munk et al., 2021), the brines being extracted for lithium are hosted in aquifers that are disconnected (on human time scales) from surface water and wetland systems at the margin of the salar while regional groundwater inflows provide critical baseflows that maintain these systems. In 2014, lithium mining made up only ∼8% of total freshwater extraction in the basin whereas copper mining made up ∼51%; these values are representative of the approximate average annual extraction rate over the past decade.…”

“…Sampled waters were grouped into seven physical water types to facilitate the interpretation and communication of our results. These distinctions are based on extensive knowledge of the regional hydrogeology gathered during more than 10 field campaigns, previously published works, and scrutiny of geochemical signatures (Munk et al., 2021). Nucleus Brines are groundwaters from the core of the halite‐dominated brine aquifer, sampled at shallow depths <13 m below ground level (mbgl), and Marginal Brines are groundwaters from the margins of the brine aquifer, sampled at the water table (<2 mbgl).…”

“…The halite‐rich brine aquifer, within the nucleus, is currently being exploited for its lithium resource (Munk et al., 2016). Geochemical evidence and physical hydrogeological conceptualization (Munk et al., 2021) do not support a source of modern groundwater inflow to the brine aquifer, while Boutt et al. (2016) document recharge to the brine body through direct precipitation and infiltration of surface waters that accumulate along the halite nucleus margin.…”

Hydroclimatological Patterns and Limnological Characteristics of Unique Wetland Systems on the Argentine High Andean Plateau

“…A similar case can be made for Azul, Los Aparejos, and Negra, which reside in adjacent basins, where Los Aparejos represents an intermediate composition but appears to have similar hydrogeological characteristics. This is consistent with basins on the Chilean Altiplano and the Salar de Atacama where dense brines can be explained through the intense and progressive evapoconcentration of much fresher inflow waters near the basin floors either as groundwater exiting the ground from long flow paths or ephemeral flow from precipitation events [21,22,102].…”

“…These hydrological imbalances within a catchment may be reconciled by the subsurface interbasin flow between topographic drainages and/or the draining of stored groundwater recharged during wetter periods hundreds to thousands of years before the present [16]. These processes are well documented globally [13,[16][17][18]; and particularly in the Chilean pre-Andean depression, where relevant contributions have been made recently [19][20][21][22]. As in other arid regions of South America, these kinds of studies are relatively scarce in Argentina.…”