Hydrochemical and stable isotopes (H, O, S) signatures in deep groundwaters of Parana 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. H-2 and O-18 data in circa 580 rainwater samples at Sao Paulo State have been selected, showing a wide dispersion (delta O-18 from -21.5 to +4.9 parts per thousand V-SMOW; delta H-2 from -162 to +43.2 parts per thousand V-SMOW). The H-2 and O-18 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 delta O-18 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 delta O-18(SO4) and delta O-18(water) data indicated that the dissolved sulfate is obtained from previous sulfate dissolution. The delta S-34 and delta O-18(sulfate) 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 delta S-34 and delta O-18(sulfate) changes along the GAS transect, accompanying the groundwater flow direction.