The use of isotopes in evolving groundwater circulation models of regional continental aquifers: The case of the Guarani Aquifer System

Abstract

The Guarani Aquifer System (GAS) has been studied since the 1970s, a time frame that coincides with the advent of isotopic techniques in Brazil. The GAS isotope data from many studies are organized in different phases: (a) the advent of isotope techniques, (b) consolidation and new applications, (c) isotope assessments and hydrochemistry evolution, and (d) a roadmap to a new conceptual model. The reasons behind the phases, their methodological approaches, and impacts on the regional flow conceptual models are examined. Starting with local δ2H and δ18O assessments of values for water fingerprinting and estimates of recharge palaeoclimate scenarios, studies evolved to more integrated approaches based on multiple tracers. Stable isotope application techniques were consolidated during the 1980s, when new dating approaches dealing with radiogenic and heavy isotopes were introduced. Through the execution of an international transboundary project, the GAS was studied and extensively sampled for isotopes. These results have triggered wider application of isotope techniques, reflecting also world research trends. Presently, hydrochemical evolution models along flow lines from recharge to discharge areas, across large‐scale tectonic features within the entire sedimentary basin, are being combined with residence time estimates at GAS outcrop areas and deep confined units. In a complex system, it is normal that many, and even contradictory hypotheses are proposed, but isotope techniques provide a unique chance to test them. Stable isotope assessments are still needed near recharge areas, and they can be combined with groundwater classical dating procedures, complemented by newer techniques (3H‐3He, CFCs, and SF6). Recent noble gas sampling and world pioneer analytical efforts focused on the confined units in the GAS will certainly led to new findings on the overall GAS circulation. The objective of this article is to discuss how isotope information can contribute to the evolution of conceptual groundwater flow models for regional continental aquifers, such as the GAS.

Structural, hydrogeological and hydrochemical characterization of aquifers in the Paraná Basin: An integrated literature review

“…This same mechanism was aborded by Strieder, et al, (2017) in Rio Grande do Sul state, showing a similarity of tectonic events in the southern part of the Paraná Basin. Deep normal faults were responsible for regulating the discharge and recharge of groundwater flow and allow hydrogeochemical differentiation (Kirchheim, et al, 2019), reinforcing the connection between structural framework and hydrochemical characteristics of Paraná Basin groundwaters.…”

“…When the amounts of salinity between the GAS and the SGAS are the same, there is a hydraulic connection between these two aquifers, with a vertical extension of 400-500 m which allow the ascent of aquifer waters under the SGAS with mineralized waters originating from mixture (Scheibe & Hirata, 2008). Research, Society and Development, v. 10, n. 9, e26610918390, 2021 (CC BY 4.0) | ISSN 2525-3409 | DOI: http://dx.doi.org/10.33448/rsd-v10i9.18390 7 Source: Geological profiles and Paraná Basin Map adapted from (Kirchheim, et al, 2019;Machado, 2005).…”

“…Athayde, et al, (2014) Clear hydrogeochemical modification of samples to the west of the Ponta Grossa arch in Paraná, showing the importance of major faults in hydrogeochemical differentiation. Kirchheim, et al, (2019) Contextualization of the evolution of the study of the Guarani aquifer in history and the recent .importance of stable isotopes in the current understanding of the Paraná Basin.…”

Aplicação do isótopo radioativo de carbono (14c) na determinação de tempos de residência em aquíferos

“…O estudo realizado pode servir de guia para o gerenciamento sustentável do aquífero na região. KIRCHHEIM et al (2019) fizeram uma síntese dos estudos isotópicos desenvolvidos no sistema aquífero Guarani, demonstrando a importância dessas análises na construção de modelos de circulação regional em grandes aquíferos. A aplicação do método de carbono-14 ocorreu ainda na fase inicial dos estudos da Bacia do Paraná, juntamente com o estudo dos isótopos ambientais.…”

Relações causais e persistências na dinâmica da disponibilidade hídrica para a formulação de modelos hidrológicos conceituais

“…O SAG é composto por arenitos de origem eólica do período Jurássico (Formação Botucatu) e de origem fluvio-eólica do período Triássico (Formação Piramboia), e em grande parte encontra-se confinado por derramamentos basálticos ocorridos no período Cretáceo (Formação Serra Geral). Ele atende a demanda por água de mais de 90 milhões de pessoas da Argentina, Brasil, Paraguai e Uruguai (KIRCHHEIM et al, 2019), e é uma das mais importantes reservas de água subterrânea da América do Sul. A ocorrência do processo de recarga e a correspondente vulnerabilidade à contaminação antrópica (e.g., por nitrato, nutrientes, pesticidas) motiva a condução de estudos experimentais em áreas de afloramento do SAG a fim de desenvolver estratégias para proteger e garantir um uso sustentável desse sistema aquífero (OEA, 2009; SINDICO; HIRATA; MANGANELLI, 2018).…”