Deciphering water sources and fluxes in the Iberá area: an isotope hydrological assessment

ORTEGA, LUCIA; MANZANO, MARISOL; VIVES, LUIS; MIRA, ANDRES; RODRÍGUEZ, LETICIA; ARAGUÁS-ARAGUÁS, LUIS; HEREDIA, JAVIER; ZABALA, MARÍA E.; ARMENGOL VALL, SANDRA

Paris

Conferencia; ISARM 2021, 2nd International Conference: Transboundary aquifers: challenges and the way forward; 2021

UNESCO

The Guaraní Aquifer System (SAG) is one of the largest and the most important transboundary aquifer in Latin America. The Iberá area, which encompasses a large wetland zone and its surroundings, located above the southern portion of the SAG in Argentina, is the focus of this study. This work builds on recent hydrogeological results in the area. A revised hydrogeological conceptual model has been postulated, proposing a better-defined geometry of the aquifer units and revised groundwater flow patterns. Groundwater flow in this part of the SAG is complex and mainly controlled by regional faults, leading to difficulties in determining the main flow paths and potential admixtures. Identifying leakages and interconnections between different aquifer units is essential for water management since these processes affect groundwater´s physicochemical characteristics and renewal time. Using a multi-tracer approach and End Member Mixing Analysis, we aimed to validate the hypothesis of a widespread occurrence of groundwater interconnections between various aquifer units. These models were used to better assess groundwater provenance, define mixing patterns in sampled wells and identify potential groundwater discharge areas into surface water bodies. A regional hydrochemical and isotopic study was conducted in lagoons, rivers and wells with the support of IAEA, Spain MICIN and IHLLA. End Member Mixing calculations clearly showed mixing between different aquifer units and the existence of two main mixing groups, one dominated by SAG water signature and another one dominated by Pre-SAG water. The geological structure controls, to a large extent, the distribution of both types of mixed waters. All surface water samples are poorly mineralized, and their chemical and isotopic properties are coherent with the signature of rainwater. 222Rn activities, used to identify groundwater discharge, do not suggest the existence of generalized groundwater discharge into surface water bodies, except at the S of the Iberá lagoon and in the Miriñay River, where the isotopic signature suggested shallow recent groundwater discharge.El libro de actas fue publicado en formato digital en: https://unesdoc.unesco.org/ark:/48223/pf0000380029 (SIGEVA no me permite cargar este URL).