Revealing Paleo-Groundwater and Interbasin Flow as Fundamental to Water
and Mineral Resource Sustainability on the Arid Altiplano-Puna Plateau
Abstract
Accelerating demand for energy storage has led to increasing development
of brine resources in the “Lithium Triangle”, estimated to hold about
75% of the planet’s Li reserves but persistent and fundamental
questions regarding the source and transit time of groundwater have
confounded efforts to manage these resources effectively. The basins
containing these brines lie within the massive Altiplano-Puna Plateau,
home to people whose ancestors have inhabited this land for thousands of
years and fragile ecosystems that exist nowhere else on Earth. This
region is very dry, bordering Earth’s driest non-polar desert and as
such, groundwater is the predominant and, in many areas the only source
of water. Fundamental questions about the spatiotemporal dimensions of
these groundwater systems have only begun to be addressed. In much of
this extreme and remote region, there is a severe lack of quality
baseline understanding of the regional hydrological system and
connections between surface and groundwater bodies. To address these
questions, we utilize an exhaustive set (~2,500
individual analyses) of environmental tracer data (δ18O, δ2H, 3H,
87Sr/86Sr), and dissolved major and minor elements in waters collected
from over a dozen field campaigns in the Salar de Atacama and Altiplano
of Chile and on the Puna Plateau of Argentina. Our integrated analysis
pairs these data with rigorous geochemical modelling and physical
hydrological measurements from the field and remote sensing products. 3H
data show much of the groundwater currently discharging into these
basins is non-modern (>60 yrs. old), stable isotope and
geochemical data show strong connectivity but also a marked disconnect
between some recharge and discharge areas. We show that “fossil”
groundwater, 100-10,000 yrs. or older is widespread and fundamental to
the system, sharp disconnects exist between the modern hydrological
system, the water bodies it sustains, and those sustained by
paleo-recharge water. By defining these connections in spatial detail
and within a regional integrated framework, we greatly improve the
fundamental mechanistic understanding of this and other
groundwater-sustained systems. This will greatly improve the ability of
communities, governments and industry to manage of these water resources
in a way that is genuinely sustainable.