Impact of afforestation on coastal aquifer recharge. Case study: eastern coast of the Province of Buenos Aires, Argentina

Abstract

The effects of afforestation on groundwater recharge—which is the only source of drinking water supply in the Pinamar District (Partido de Pinamar), located on the eastern coast of the Province of Buenos Aires, Argentina—are analysed. The study area is characterised by a sand-dune barrier parallel to the coast, where freshwater lenses accumulate. These are bounded to the west by the brackish water of the continental plain and to the east by the seawater. Soil texture makes it possible to infer the infiltration capacity. Methods associated with groundwater table fluctuations, hydrodynamics, hydrochemistry and the characteristics of stable isotopes (2H and 18O) in groundwater were used. In order to confirm the results, daily water balances were carried out. Recharge variations were quantified based on periodic groundwater table records and water balances. A decrease in recharge was verified in forested areas with respect to non-forested areas (bare soil). The groundwater flow (hydraulic gradients), the electrical conductivity of groundwater and the fractionation of stable isotopes indicate that the higher evapotranspiration in areas with tree cover leads to a decrease in water surplus and in the possibilities for groundwater table recharge. The effects of afforestation on recharge and, therefore, on good-quality shallow groundwater reserves constitute a key element in planning the sustainable use of the water resources.