Isotopic insights on continental water sources and transport in the mountains and plains of Southern South America

ABSTRACT

Hosting the flattest sedimentary plains and highest Andean range of the continent, southern South America faces hydrological transformations driven by climate and land use changes. Although water stable isotopes can help understand these transformations, regional synthesis on their composition is lacking. We compiled for the first time a dataset of H and O isotopic composition for 1659 samples (precipitation, rivers, groundwater and lakes) along latitude (22.4°S to 41.6°S), longitude (55.3°W to 71.5°W), elevation (1–4700 m) and precipitation (∼50 to ∼1500 mm/a) gradients encompassing the Chaco-Espinal-Pampas plains, their adjacent Andean Cordillera and smaller mountain ranges in-between. Emerging patterns reveal (i) only slight seasonal isotope trends in precipitation with no effects of event size, (ii) Atlantic/Amazonian vs. Pacific moisture supply to rivers north and south of the ‘arid diagonal’ of the continent, respectively, (iii) uniform isotopic composition in Atlantic/Amazonian-fed rivers vs. poleward isotope enrichment in Pacific-fed rivers caused by the elevation decline of the Andes, (iv) strong direct evaporation effect in rivers and shallow (<1 m) phreatic groundwater of the plains. We provide the first integrated water isotope geographical patterns of southern South America helping to improve our understanding of its water cycling patterns at the atmosphere and the land.

KEYWORDS:

• d-excess
• GNIP and GNIR
• groundwater evaporation
• hydrogen-2
• isotope hydrology
• mountains
• oxygen-18
• precipitation recycling
• sedimentary plains
• South America‌

Acknowledgements

We acknowledge all contributing researchers to GNIP and GNIR databases, as well as the effort of the IAEA for initiating and maintaining these open access global initiatives. We thank Ricardo Paez, Sofía Guell and Raúl Giménez for field and lab assistance. Many colleagues have provided invaluable help sampling water bodies throughout Argentina, Paraguay and Uruguay; we are particularly thankful to Gervasio Piñeiro in this regard. We appreciate the insightful comments of two anonymous reviewers and the Editor-in-Chief Dr Gerhard Strauch and Associate Editor Dr David Soto that significantly improved the quality of the manuscript.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was supported by the Fondo para la Investigación Científica y Tecnológica under FONCyT-Grant BID PICT-2018-03143.