Processes controlling groundwater salinity in coastal wetlands of the southern edge of South America

The Argentine Atlantic coast constitutes an extensive area where numerous wetlands develop under humid, semi-arid and arid conditions, in which there are also variations in relation to tidal influence with estuarine, mixing and marine areas. The aim of this work is to conduct a comparative study on the processes controlling the groundwater salinity in medium to high latitudinal coastal wetlands of four natural reserves with contrasting hydrological and climatic conditions. In each study area a monitoring network was established where the content of CO32-, HCO3-, Cl-, SO42-, Ca2+, Mg2+, Na+, K+, delta H-2 and delta O-18 of the water were determined. The results show a saline groundwater increase along a latitudinal gradient with electrical conductivities varying from 0.3 mS/cm at 34 degrees 47 S to 154 mS/cm at 42 degrees 25' S. The results obtained show that the ionic contents in groundwater are partially controlled by the salinity of the tidal flood water whose electrical conductivity varies from 0.3 mS/cm in the Rio de la Plata estuary to 52 mS/cm in the sea water of the southern study area. In the southern wetlands, where an increase of aridity is also registered, there is a clear increase in groundwater ionic concentrations, which occurs without isotopic enrichment indicating processes of salts dissolution of the sediments. The evaporites precipitation occurs due to the total evaporation of the tidal water that floods the wetlands in spring high tides. The salinization of groundwater responds to natural processes inherent to the hydrological, climatic and lithological characteristics of each wetland. Given that the areas studied correspond to natural reserves, the results generate databases that will allow the identification of future changes in salinity associated with anthropic influences or changes in hydrological and/or climatic conditions as a result of climate change. (C) 2020 Elsevier B.V. All rights reserved.

Automated summary

The study conducted a comparative analysis of groundwater salinity in coastal wetlands of four natural reserves in Argentina, finding an increase in salinity along a latitudinal gradient. The results showed that the ionic contents in groundwater were partially controlled by the salinity of tidal flood water, with the southern wetlands experiencing a significant increase in groundwater ionic concentrations.