Geochemical Mechanism Controlling Pampasic Ponds Hydrochemistry: Salado River Drainage Basin, Argentina

Chemical analyses of major ions performed in some of the Pampasic ponds located in the lower reach the Salado River showed a similar composition to that of shallow groundwater, i.e., the total dissolved solids ranged between 1 g/l and 2 g/l, sodium was the most abundant among the cations and accounted (meq/l) for 80.6%. Calcium amounts were 6.5% while magnesium was 9.9%. Potassium was less abundant with a mean value of 3.0%. Appreciable differences between summer and winter values were not observed. Since groundwater was the main source of surface water, a possible geochemical mechanism was proposed in order to achieve better understanding of the Pampasic pond?s water chemistry. The processes that seem to be responsible for groundwater hydrochemistry are: cation exchange, ancient marine sediments dissolution and aluminosilicate weathering. The differences observed between surface water and shallow groundwater composition with respect to an additional enrichment in sodium may be attributed to the evaporation-crystallisation process promoting calcite precipitation.