See discussions, stats, and author profiles for this publication at: https://www.researchgate.net/publication/332702203 The use of isotopes in evolving groundwater circulation models of regional continental aquifers: The case of the Guarani Aquifer System Article in Hydrological Processes · April 2019 DOI: 10.1002/hyp.13476 CITATIONS READS 0 74 4 authors, including: Roberto Kirchheim Didier Gastmans Companhia de Pesquisa de Recursos Minerais São Paulo State University 33 PUBLICATIONS 10 CITATIONS 45 PUBLICATIONS 189 CITATIONS SEE PROFILE SEE PROFILE Hung Kiang Chang São Paulo State University 172 PUBLICATIONS 902 CITATIONS SEE PROFILE Some of the authors of this publication are also working on these related projects: AVALIAÇÃO TOXICOLÓGICA DE PRODUTOS EMPREGADOS NO CULTIVO DA CANA-DE-AÇÚCAR SOBRE ORGANISMOS NÃO ALVOS View project Complementary Isotopic Studies in the Southern, Western and Eastern Compartments of the Guarani Aquifer System (Brazil) - Groundwater Dating Along Defined Flow Paths View project All content following this page was uploaded by Roberto Kirchheim on 16 July 2019. The user has requested enhancement of the downloaded file. Received: 8 December 2017 Accepted: 5 April 2019 DOI: 10.1002/hyp.13476 SI STABLE ISOTOPES IN HYDROLOGICAL STUDIES The use of isotopes in evolving groundwater circulation models of regional continental aquifers: The case of the Guarani Aquifer System Roberto Eduardo Kirchheim1 | Didier Gastmans2 | Hung Kiang Chang3 | Troy E. Gilmore4 1 Hydrology and Territorial Management Directory (DHT), The Geological Survey of Abstract Brazil (CPRM‐SGB), São Paulo (SP), Brazil The Guarani Aquifer System (GAS) has been studied since the 1970s, a time frame 2 Environmental Studies Center (CEA), São that coincides with the advent of isotopic techniques in Brazil. The GAS isotope data Paulo State University (UNESP), Rio Claro (SP), Brazil from many studies are organized in different phases: (a) the advent of isotope tech- 3 Laboratory for Hydrogeology and Basin niques, (b) consolidation and new applications, (c) isotope assessments and Studies (LEBAC), São Paulo State University hydrochemistry evolution, and (d) a roadmap to a new conceptual model. The reasons (UNESP), Rio Claro (SP), Brazil 4 Conservation and Survey Division, School of behind the phases, their methodological approaches, and impacts on the regional flow Natural Resources, University of Nebraska‐ conceptual models are examined. Starting with local δ2H and δ18O assessments of Lincoln, Lincoln, (NE), USA values for water fingerprinting and estimates of recharge palaeoclimate scenarios, Correspondence studies evolved to more integrated approaches based on multiple tracers. Stable iso- Roberto Eduardo Kirchheim, The Geological Survey of Brazil (CPRM‐SGB). Rua Costa 55, tope application techniques were consolidated during the 1980s, when new dating CEP 01304‐010, São Paulo (SP), Brazil. approaches dealing with radiogenic and heavy isotopes were introduced. Through Email: [email protected] 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. KEYWORDS groundwater management, Guarani Aquifer System, stable isotopes Hydrological Processes. 2019;1–13. wileyonlinelibrary.com/journal/hyp © 2019 John Wiley & Sons, Ltd. 1 2 KIRCHHEIM ET AL. 1 | INTRODUCTION The Mesozoic aged continental clastic units from the Paraná and Chacoparanaense sedimentary basins were grouped as GAS units, In the last 60 years, abundant information on isotopes in groundwater named to recognize the indigenous people of the Great Guarani has been obtained, and widespread application to hydrogeological Nation who used to live in this same region (Organization of American research has recently increased because analytical techniques have States (2009). become faster, more sensitive, and less expensive (Wassenaar, Coplen, Collectively, GAS resources are shared by more than 90 million & Aggarwal, 2014). The sustainable use and management of aquifers people from Argentina, Brazil, Paraguay, and Uruguay, for whom it require an understanding of aquifer hydrogeology and groundwater represents the most important source for public water supply, agricul- dynamics. This understanding can be gained over a period of decades ture, and industrial uses as well (Organization of American States by observations and measurements of precipitation, river flows, and (2009)). At a regional scale, Vives, Rodriguez, and Goméz (2008) have groundwater levels. Isotope techniques and particularly those that identified a water deficit condition, where GAS annual extraction esti- can be applied to estimate the residence time of groundwater help mates (1.04 km3/year) are higher than recharge (0.8 to 1.4 km3/year). to cost‐effectively build a conceptual framework of aquifer hydrogeol- According to Gastmans, Veroslavsky, Chang, Caetano‐Chang, and ogy and flow system. Pressinotti (2012), despite the calculation uncertainties, this balance The use of the radioactivity of 14C and 3H isotopes for estimating scenario should be strongly considered for GAS management planning. groundwater age, aquifer storage, rate of groundwater renewal, and In some areas of the State of São Paulo, GAS drawdowns are already flow velocity was identified in the 1940s (Libby, 1946). Groundwater well known leading to economical externalities. According to Manzano age provides unmatched advantages for improving numerical models and Guimaraens (2012), who conducted an extensive hydrochemical of groundwater flow in large, regional aquifers where water level data assessment covering the entire GAS body, the great majority of the are normally scarce (Aggarwal, 2013), such as the Nubian Aquifer, water was found to be of very good quality and suitable for domestic whose model calibration was based on 36Cl and 81Kr residence times consumption and agricultural use. Anthropogenic contamination has estimates (Sturchio et al, 2004; Patterson et al., 2003. been detected only at some GAS outcrops and adjacent semiconfined The use of environmental isotopes in hydrological studies in Brazil areas. Sound management of such a transboundary aquifer demands started at the end of the 1960s and early 1970s, with focus on the strategic action mechanisms against overexploitation at confined and semi‐arid northeast region, followed by the Amazonia region, storage‐controlled areas and protection of recharge areas where basal and, finally, the southeast regions, lying within the Paraná flows are being produced through hydraulic connection to the surficial intracratonic basin (Silveira & Silva Junior, 2002). These early studies drainage network. were motivated by the need to understand the groundwater saliniza- The purpose of this article is to present the continuous evolution tion processes, aquifer recharge mechanisms, and groundwater ages of the isotope knowledge of the GAS, pointing out how determinant in semi‐arid and densely populated areas (Gat, Mazor, & Mercado, these studies were in promoting enhanced insights over its regional 1968). Salati et al. (1974) offer an overall synthesis of isotope studies flow and hydrochemical evolution dynamics. Isotope assessments, during this period. In the Amazonia region, on the other hand, daily conducted locally and across the entire GAS, helped to shape the δ18O and δ2H data for moisture and rain water allowed researchers actual GAS hydrogeological knowledge and enhanced the evolving to recognize the relevance of water recycling within the continental conceptual models. The isotope application novel in the GAS is coher- hydrographic basin and the importance of the forest evapotranspira- ent with the evolution of the technical developments worldwide. At tion in determining rain patterns (Salati, Dall'Olio, Matsui, & Gat, the other hand, it offers valuable lessons learned with possible replica- 1979). Finally, isotope initiatives at the southeast region began with tion in other regional aquifer systems, such as the Congo, Kalahari, isotopic fingerprinting for rain and groundwater, including samples Karoo, Nubian, Taoudeni‐Tanezrouft, Senegalo‐Mauritanian, Yakut, from the Botucatu and Pirambóia Formations (actually belonging to Angara‐Lena, High Plains, Great Plains, Floridian, Edwards, Gulf the Guarani Aquifer System [GAS]), considered to be the most promi- Coastal Plain, and Great Artesian Basin (Aggarwal et al., 2014). nent aquifer units of the Paraná Basin (Matsui et al., 1971). The