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

The Pampean plain is one of the most extended regions of the world. In this plain there are numerous shallow lakes that have different origins associated with climate changes at the end of the Quaternary period. Chasico Lake is the main waterbody in the southwest of the Chaco-Pampean plain. It shows some differences from the typical Pampean shallow lakes. The aim of this paper is to explain the geochemical process that determines the chemical composition of the water of Chasico Lake. The results show that the groundwater is sodium bicarbonate type. Chebotarev's diagram indicates that the cation-exchange takes place in groundwater. The surface water of Chasico Lake is sodium chloride type. Gibbs's diagram shows that the geochemical processes that affects the Chasico) 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 V concentrations were studied in surface and groundwater showing significant correlations in groundwater between As vs. F (r = 0.99, p < 0.05), As vs. V (r = 0.99, p < 0.05) and V vs. F (r = 0.99, p < 0.05), while in surface water it was only found for As vs. F (r = 0.91, p < 0.05). The As, F and V concentration values were higher and more widely dispersed in surface water than in groundwater, as a consequence of evaporation. The fact that these elements do not correlate in surface water may also indicate a different origin. (C) 2014 Published by Elsevier B.V.