Hydrodynamic and hydrochemistry of wet meadows and shallow lakes in areas of the Patagonian basaltic plateaus, Argentina

Abstract

Extra-Andean Patagonia, located in the south end of South America, is a wide arid region where the basaltic plateau landscape dominates. Associated with the basaltic plateaus, wet meadows and shallow lakes make up environments of relevance due to the ecosystemic services they provide. The aim of this work was to define the processes and factors that condition the hydrodynamics and hydrogeochemistry of wet meadows and shallow lakes in a sector of the Patagonian plateau basalts. For this, detailed geological and geomorphological studies were carried out and water was sampled at 29 points for the analysis of major ions and, in some samples, stable isotopes of the water molecule. Values of δ18O and δ2H similar to the local meteoric line in the water of wetmeadows indicate that rainwater quickly infiltrates through the fractures of the basaltic plateaus and stores in the underlying sediments. Groundwater discharge occurs in the scarp zone due to changes in sediment permeability. The weathering of silicates in basalts, ion exchange in the sediment clays, and the dissolution of soluble salts provided by the dust control water chemistry of this wetland.Water from wet meadows drains into saline endorheic basins of sodium chloride composition where the isotopic signal is indicative of evaporation percentages close to 95%. The high evaporation rates cause the precipitation of evaporitic salts at the edges of shallow lakes with carbonate, sulfate, and chloride species controlled by the dominance of sodium in the water.