Recharge and residence times of groundwater in hyper arid areas: The confined aquifer of Calama, Loa River Basin, Atacama Desert, Chile

Christian Herrera; Linda Godfrey; Javier Urrutia; Emilio Custodio; Teresa Jordan; Jorge Jódar; Katherine Delgado; Fabiola Barrenechea

doi:10.1016/j.scitotenv.2020.141847

Recharge and residence times of groundwater in hyper arid areas: The confined aquifer of Calama, Loa River Basin, Atacama Desert, Chile

Sci Total Environ. 2021 Jan 15:752:141847. doi: 10.1016/j.scitotenv.2020.141847. Epub 2020 Aug 22.

Authors

Christian Herrera¹, Linda Godfrey², Javier Urrutia³, Emilio Custodio⁴, Teresa Jordan⁵, Jorge Jódar⁶, Katherine Delgado⁷, Fabiola Barrenechea⁸

Affiliations

¹ Centro de Investigación y Desarrollo de Ecosistemas Hídricos, Universidad Bernardo O'Higgins, Santiago, Chile. Electronic address: christian.herrera@ubo.cl.
² Earth and Planetary Sciences, Rutgers University, 610 Taylor Road, Piscataway, NJ 08854, USA.
³ HEUMA, 2030. Department of Mining Engineering, Universidad de Antofagasta, Antofagasta, Chile.
⁴ Groundwater Hydrology Group, Dept. Civil and Environmental Engineering, Technical University of Catalonia (UPC), Barcelona & Royal Academy of Sciences of Spain, Spain.
⁵ Department of Earth & Atmospheric Sciences and Atkinson Center for a Sustainable Future, Snee Hall, Cornell University, Ithaca, NY 14853-1504, USA.
⁶ Geological and Mining Institute of Spain (IGME), Zaragoza, Spain.
⁷ Centro de Investigación y Desarrollo de Ecosistemas Hídricos, Universidad Bernardo O'Higgins, Santiago, Chile.
⁸ Escuela Ciencias de la Tierra, Observatorio en Gestión de Riesgo de Desastres de la Universidad Bernardo O'Higgins, Santiago, Chile.

PMID: 33207522
DOI: 10.1016/j.scitotenv.2020.141847

Abstract

Groundwater recharge in hyper arid areas often depends on surface water infiltration and diffuse recharge of highly evaporated precipitation only contribute under favorable conditions. This happens in the Calama basin two-aquifer system, in the Central Andean area of northern Chile. A conceptual model of the groundwater system and its relationship with the Loa River is defined. We focus on the confined aquifer of the Calama basin, combining hydrodynamic, hydrogeochemical and isotopic methods. Radiocarbon (¹⁴C) activity data of dissolved inorganic carbon (DIC), in conjunction with chemical data, are applied to evaluate groundwater residence time within the confined aquifer. The Loa River recharges the Calama basin aquifers in its northeastern part, with water that has chemical and isotopic characteristics inherited from the arid environment and volcanic rocks in its upper basin. In the central and northeastern part of the confined aquifer, minor variations in chloride concentration suggest that the deep aquifer is well confined. The δ¹⁸O and δ²H values in groundwater of the confined aquifer show an increasing isotopic fractionation from the recharge area (around -10‰ δ¹⁸O) to those in the discharge area (between -8.5‰ and -8‰) in the southwestern part of the aquifer. The ¹⁴C activity continuously decreases down flow from the recharge by the Loa River. Adjusted DIC radiocarbon ages indicate a groundwater travel time between 1500 and 4000 years in the confined aquifer of Calama. Despite the limitations and uncertainties of radiocarbon in DIC to estimate groundwater transit times for the confined aquifer and considering complementary chemical and isotopic constraints, the DIC ¹⁴C provides acceptable values. The approach may be applicable in other confined aquifers in hyper-arid climates in which the formation of aquifer systems linked to river damming by geological action took place. This information is needed for sound management of the scarce groundwater resources.

Keywords: (14)C((DIC)); Arid zones; Confined aquifer; Groundwater; Recharge.