Stable isotopes, carbon-14 and hydrochemical composition from a basaltic aquifer in São Paulo State, Brazil

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• 作者：Didier Gastmans ; Amauri Antônio Menegário ; Ian Hutcheon
• 关键词：Serra Geral Aquifer ; Hydrochemistry ; Stable isotopes ; Groundwater age ; Brazil
• 刊名：Environmental Earth Sciences
• 出版年：2017
• 出版时间：February 2017
• 年：2017
• 卷：76
• 期：4
• 全文大小：
• 刊物类别：Earth and Environmental Science
• 刊物主题：Geology; Hydrology/Water Resources; Geochemistry; Environmental Science and Engineering; Terrestrial Pollution; Biogeosciences;
• 出版者：Springer Berlin Heidelberg
• ISSN：1866-6299
• 卷排序：76

文摘

The Cretaceous Serra Geral Aquifer (SGA) is contained within one of the largest continental flood basalts in the world, reaching a thickness up to 1700 m in the center of the Paraná Basin. The SGA is one of the most important groundwater reservoirs in northeastern São Paulo State (Brazil), responsible for water supply to cities and agriculture. In order to evaluate the geochemical and isotopic evolution of SGA, as well as to determine the mean residence time, a groundwater sampling campaign was carried out over the SGA in São Paulo State (Brazil) from January to April 2013. Two main hydrochemical facies were recognized: Ca–Mg–HCO₃ related to water–rock interaction reactions in basaltic outcrop, such as mineral dissolution due to atmospheric CO₂ uptake, and alkaline Na–HCO₃ groundwater, evolved from mixing with groundwater from the underlying Guarani Aquifer System. Stable isotope (δ18O and δ2H) ratios range from −8.87 to −5.32‰ VSMOW and −61.31 to −31.64‰ VSMOW, respectively, closely following the GMWL. Spatial and temporal variations in isotope ratios are associated with the South Atlantic convergence zone activities and the type of rain responsible for recharge. Values for δ13C vary from −21.53 to −7.11‰ VPDB, while 14C activities vary from 1.2 pcm to more than 100 pcm, presenting a trend to enrichment and decrease in 14C activities westward, concordant with the regional groundwater flow direction. Most recent groundwaters have δ13C ratio contents mostly consistent with C3 plants.