Origin of spring waters employing a multiparametric approach with special focus on stable isotopes 2H and 18O in the Lagoa Santa Karst region, Southern Brazil*

Abstract

Karst environments have an inherent complexity that interferes with their hydrogeology comprehension. Hence, isotope hydrology can be a valuable tool to assess trajectory of subsurface flows in an unexplored setting. The study area is located in the Lagoa Santa Karst, an environmental protection area of great economic, cultural and ecological importance, where Neoproterozoic metalimestones accommodate karst-fractured aquifers, characterized by complex water dynamics, essential vulnerability and high productivity. The purpose of this study was to investigate groundwater flow origins of springs using principally environmental stable isotopes 2H and 18O. Rainwater and spring water were sampled and analysed. The LMWL presents angular and linear coefficients strongly similar to those of the GMWL. Spring isotopic signatures, which represent the base flow and present wide-ranging of 2H and 18O, were separated into two groups. The first group can be associated with recent rainwater major contributions, while the second group shows significant evaporated water contributions, largely represented by resurgences. Tritium concentration and physico-chemical parameter data supported this interpretation, pointing that waters of the second group remained more time on the surface and subsurface. Therefore, using isotope tracers to evaluate upper groundwater zone in this tropical karst system is a powerful instrument for water resources management.