Hydrogeochemical processes as a conditioner of freshwater lenses associated with coastal deposits

Abstract

The aim of this work was to study the processes and factors conditioning the hydrochemistry of freshwater lenses associated with Holocene coastal deposits in an area of the Argentinean Atlantic coast. For this purpose, geomorphological units were mapped and a shallow groundwater monitoring network was established, including pre-existing boreholes and phreatimeters. During the construction of the phreatimeters, sediment samples were extracted to determine the texture and mineralogical characteristics. Four samplings were carried out to measure in situ physicochemical parameters and to determine majority ions in the water. The chemical data were analyzed considering the associated geomorphology, lithology, water balance and hydrodynamics. The hydrogeological importance of the different sand deposits lies in the fact that, being highly permeable units, they facilitate the rapid infiltration of rainwater. There, recharge occurs preferentially during water surplus periods, producing a rise in the water table. Likewise, geomorphological features have a direct influence on the dynamics of groundwater, which influences its salinity, being fresh in those of higher topographic expression. Moreover, the chemical composition of groundwater is conditioned by the interaction of water with sediments, dominating the dissolution and alteration of minerals, giving rise to the different hydrochemical facies recorded. The results obtained in this work have provided an understanding of the factors and processes that condition groundwater chemistry in coastal deposits and will contribute to the increase of knowledge related to the influence of geomorphology on the hydrochemistry of freshwater lenses.