Integrated Geophysical, Isotopic, and Hydrochemical Approach to Studying Freshwater–Saline Water Interaction in Coastal Wetland at Punta Rasa Nature Reserve, Argentina

Abstract

The interaction between freshwater and saline water in coastal wetlands generates an interfacezone where vertical and horizontal salinity gradients develop. This interface has beeninvestigated through geophysical, hydrochemical, and isotopic studies, which constituteuseful tools that provide different types of information whose combined interpretationallows for a more comprehensive understanding of the processes associated with thisinteraction. This work assessed, through an integrated geophysical (electrical resistivitytomography), hydrochemical (major ions), and isotopic (δ2H, δ18O, and 222Rn) study, thefreshwater–saline water interaction between marsh and dune environments in the PuntaRasa Natural Reserve (Argentina). Results show that salinity gradients occurring betweendune and marsh environments are associated with fresh groundwater discharge and rainwaterinfiltration. Fresh groundwater discharge takes place in topographically elevateddunes, where freshwater lenses form. This discharge generates vertical and horizontalsalinity gradients because the hydraulic gradient causes the interface to migrate with thegroundwater flow. In low-relief dunes, lenses do not develop and the salinity gradient thatdevelops within the interface due to rainwater infiltration is vertical. The findings clarifyplant zonation linked to freshwater–saline water interfaces and provide environmentaldata to assess wetland resilience to climate-driven changes.