HYDROLOGICAL CONNECTIVITY, RESIDENCE TIME AND SOLUTE TRANSPORT DYNAMICS IN THE ARID HIGH-ANDEAN LITHIUM TRIANGLE OF ARGENTINA

Many fundamental questions regarding natural hydrologic cycles in arid mountain regions remain unresolved, particularly those related to groundwater, its connectivity to surface water and between basins, and relationships between residence time and solute transport. The deep water tables and long residence times inherent to these systems lead to large uncertainties in water budgets and processes controlling groundwater fluxes across hydrological boundaries. Nowhere is the need to address these questions more apparent than the remote and extreme region of the central Andes known as the “Lithium Triangle” where recent rapid development of Lithium brine resources and the uncertain effects of Climate Change have highlighted these uncertainties. This study examines the integrated regional groundwater system on the Puna Plateau, its interaction with the modern hydrologic cycle, and how these mechanisms influence specific wetlands. We utilize a large dataset of tracers (δ¹⁸O, δ²H, ³H, ⁸⁷Sr/⁸⁶Sr), and dissolved elements from three field campaigns, paired with field hydrometric data and satellite-derived time series analysis.

We present an integrated conceptual model of groundwater dynamics among major basins, salt flats, and freshwater wetlands of the Puna. Our results outline a few novel findings regarding the hydrological attributes of this environment: i) groundwater transport and connectivity to the surface is controlled primarily by geological structure, rather than topography, ii) most of the water here is very old (pre-modern) but mean residence times vary substantially over short spatial distances, regulating many freshwater systems and controlling dynamic fresh-salt water transitional zones, iii) solute fluxes are more a function of flow path hydrogeology than residence time, and iv) stable water isotope signatures delineate clear distinctions between long-term average source waters and the decoupling of modern hydroclimate from the hydrologic system as a whole. This analysis provides critical constraints on the large uncertainties inherent to these complex systems. An improved understanding of the primary controls on water source and transport will allow us to protect communities and fragile ecosystems from the most damaging potential impacts of water extraction in these environments.