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

PUNTORIERO,ML; FERNANDEZ-CIRELLI, A; VOLPEDO, A

JOURNAL OF GEOCHEMICAL EXPLORATION

ELSEVIER SCIENCE BV

Lugar: Amsterdam; Año: 2015 vol. 150 p. 64 - 72

0375-6742

The Pampean plain, Argentina, is one of the largest regions in the world, characterized by shallow lakes. These lakes are of various origins associated with climate changes at the end of the Quaternary, but without lakes as predecessors Groundwater discharge maintain the base flow of the lakes. The water bodies located in the southwest of the plain have been poorly studied and show some differences from the typical Pampean shallow lakes. The aim of the present research was to determine the geochemical processes that explain surface water composition and its relationship with groundwater from the Chasicó locality. Samples were collected in 2010 and 2011 from the Chasicó Lake and Chasicó Stream (surface water), and in the Chasicó locality (groundwater). Water temperature and pH were measured in situ with a pH meter. The concentration of major ions was determined by standard methods. Cation-anion composition of groundwater and surface water was plotted on a Piper´s trilinear diagram, which showed that the former is of the sodium bicarbonate type, while the latter is of the sodium chloride type. On the other hand, Ca2+ + Mg2+ - (SO4- + HCO3- + CO3-) was plotted against Na+-Cl- for groundwater. A good correlation was found between them (R2=0.99), with a slope (p=-1.03) indicating a cationic exchange process between Ca2+ and Na+. The ionic composition of surface water differed from that of groundwater, which may be associated with climatic factors such as the precipitation and crystallization-evaporation processes. This difference in chemical composition suggests that groundwater is not the main source of water of the Chasicó Lake.