Groundwater salinization in arid coastal wetlands: a study case from Playa Fracasso, Patagonia, Argentina

Abstract

The origin of the high salinity in the groundwater of acoastal wetland in an arid climate was studied in the Playa Fracasso marsh, located on the northwestern coast of the extra-Andean Patagonia. Research was carried out by means of the design of a network of soil pits and short iezometers in the marsh and the surrounding landforms.Continuous fluctuations of the water table, in situ physical and chemical properties, major ions (Ca2+, Mg2+, Na+, K+, Cl−, SO42−, HCO3−) and stable isotopes (18O and 2H) in groundwater, as well as soil salinity, were measured. The combined analysis of the hydrodynamics, the ion ratios rCa2+/rCl−,and rMg2+/rCa2+vs.rCl−and the isotopic composition made it possible to recognize an area within the high marsh in which the origin of groundwater is mainly marine and another in which the contributions are of mixed origin. By means of the analysis of 18O vs. Cl−, a salinization process with no change in isotopic composition was identified. Its interpretation, together with those of the soil salinity profiles and the records of the fluctuations in electrical conductivity associated withextraordinary tides, was used to develop a conceptual model of salinization for coastal wetlands in arid zones. It consists in a cyclical mechanism of evaporatranspiration, precipitation, dissolution and transport of salts during tides.