Hydrochemical and stable isotopes (H, O, S) signatures in deep groundwaters of Paraná basin, Brazil

Abstract

This paper describes a hydrochemical (major and trace elements) and stable isotopes (H, O, S) study of rainwater and groundwater in a Guarani Aquifer System (GAS) transect at Sao Paulo State, Brazil. The Brazilian Code of Mineral Waters (BCMW) was adopted for the groundwater temperature classification, allowing adequate insights in the hydrochemical data. 2H and 18O data in circa 580 rainwater samples at Sao Paulo State have been selected, showing a wide dispersion (δ18O from −21.5 to +4.9 ‰ V-SMOW; δ2H from −162 to +43.2 ‰ V-SMOW). The 2H and 18O data in groundwater did not vary significantly, fitting the regional meteoric water line and indicating that the groundwater origin is directly related to the meteoric water precipitation. The δ18O values in groundwater collected along the GAS transect did not indicate a tendency towards more negative values according to the groundwater flow direction at Sao Paulo State as suggested elsewhere. The δ18OSO4 and δ18Owater data indicated that the dissolved sulfate is obtained from previous sulfate dissolution. The δ34S and δ18Osulfate data of dissolved SO42− suggested that the dissolution of evaporites and bacterial SO42− reduction processes may be occurring at the GAS. The temperature, redox potentials, dissolved oxygen and organic matter content in the sediments provided an ideal environment for the δ34S and δ18Osulfate changes along the GAS transect, accompanying the groundwater flow direction.