Informations et ressources scientifiques
sur le développement des zones arides et semi-arides

Titre : FUNDAMENTAL CONTROLS ON THE WATER CYCLE IN ARID ENVIRONMENTS : A MECHANISTIC FRAMEWORK FOR SPATIOTEMPORAL CONNECTIVITY BETWEEN HYDROCLIMATE AND GROUNDWATERS IN THE DRY ANDES

Auteur : Moran, Brendan J.,

Etablissement de soutenance : University of Massachusetts Amherst

Grade : Doctor of Philosophy (PhD) 2022

Résumé
There remain many persistent uncertainties regarding fundamental aspects of natural water cycles in arid mountainous regions, the Dry Andes of South America represents one of the most extreme examples of these environments on the Planet. Deep water tables (>100 meters), long groundwater transit times and distances (>100 years, 10-100 kilometers), limited and infrequent rainfall, remote and difficult to access terrain, and complex salar/evaporite hydrogeology common in these environments make reliable monitoring of these hydrological systems particularly difficult. As a result, major gaps remain in our understanding of critical aspects of the water cycle such as recharge and evaporation rates, source and transport of major groundwater flow paths, and interactions between modern hydroclimate systems and old regional groundwater systems. A particular focus is the Salar de Atacama basin in Chile and its massive evaporite deposit, world-class lithium-brine, and unique saline lagoons but we also investigate many other endorheic basins across the adjacent plateau in Chile and Argentina. In this hyper arid-to-arid region, groundwater is a vital resource, sustaining both societies and ecosystems but the increasing development of fresh and saline groundwater for mineral extraction (particularly lithium and copper) along with the uncertain impacts of global climate change pose serious challenges to managing this water responsibly into the future.

The chapters that follow describe our work to address these fundamental questions and improve our understanding of these complex hydrological systems and provide the knowledge and tools to better manage these vital resources. We utilize a variety of geochemical, hydrophysical, and remote sensing techniques to probe these systems and then integrate this understanding to constrain, quantify, and conceptually describe their various attributes. Key methods we have pioneered here include the measurement of the radioactive isotope of hydrogen tritium to assess the relative content of contemporary and relic waters. By collecting large datasets over several years covering a representative sample of water bodies within these basins and pairing these data with other geochemical tracers including δ18O, δ2H, and Cl- we have shown this to be a powerful tool to probe these questions in this data-poor region. The additional layer of satellite-based hydroclimatological assessment, hydrophysical measurements in the field, and conceptual and analytical models allow us to place critical constraints on fundamental controls on water cycles in these environments.

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