Geochemical mechanisms controlling the chemical composition of groundwater and surface water in the southwest of the Pampean plain (Argentina)

Abstract

The Pampean plain is one of the most extended regions of the world. In this plain there are numerous shallowlakes that have different origins associated with climate changes at the end of the Quaternary period. ChasicóLake is the main waterbody in the southwest of the Chaco-Pampean plain. It shows some differences from thetypical Pampean shallow lakes. The aim of this paper is to explain the geochemical process that determines thechemical composition of thewater of Chasico Lake. The results showthat the groundwater is sodiumbicarbonatetype. Chebotarev´s diagram indicates that the catión-exchange takes place in groundwater. The surface water ofChasicó Lake is sodium chloride type. Gibbs´s diagram shows that the geochemical processes that affects theChasicó Lake are evaporation and crystallization, being the water of the lake similar to seawater. The BEI(Base Exchange Index) shows that the process of cation-exchange in the water is not relevant. As, F and Vconcentrations were studied in surface and groundwater showing significant correlations in groundwaterbetween As vs. F (r=0.99, p b 0.05), As vs. V (r=0.99, p b 0.05) and V vs. F (r=0.99, p b 0.05),while in surfacewater it was only found for As vs. F (r = 0.91, p b 0.05). The As, F and V concentration values were higher andmore widely dispersed in surface water than in groundwater, as a consequence of evaporation. The fact thatthese elements do not correlate in surface water may also indicate a different origin.