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Integrating Traditional Hydrogeology and Radon-222 to Characterize Groundwater Loss to the Sea in a Peri-Urban Coastal Aquifer in Argentina
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DOI：10.1002/hyp.70638.png)
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Abstract
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Coastal freshwater resources are increasingly vulnerable as climate warming and altered precipitation patterns intensify stress on low-lying sandy aquifers, particularly in rapidly urbanizing regions. Reduced rainfall, higher evaporation and growing water demand from tourism and population expansion limit recharge. In Latin America, where many major cities lie along the coast and impervious surfaces continue to increase, understanding hydrological pathways is essential to evaluate freshwater availability under rising environmental pressures. An often overlooked component of coastal water budgets is submarine groundwater discharge (SGD), the subsurface flow of groundwater into the sea. While recirculated saline SGD has limited impact on freshwater reserves, the freshwater fraction (fSGD) represents a true loss from aquifers; its omission from recharge–runoff assessments leads to systematic overestimation of groundwater availability, especially in sandy coastal barriers with minimal surface water storage. This study investigates groundwater transport and SGD dynamics in the sandy coastal aquifer of Buenos Aires Province, Argentina, using a combined approach based on 222Rn activity and hydrogeological parameters. 222Rn concentrations were measured in wells and along a nearshore transect ~200 m from the shoreline, complemented by groundwater depth, electrical conductivity, temperature and contour maps. No significant correlations were observed between 222Rn and electrical conductivity, temperature, groundwater depth, geomorphology, or unsaturated zone thickness. 222Rn showed an inverse relationship with the precipitation regime, and sectors previously affected by marine intrusion exhibited the lowest activities. Comparisons of SGD estimates revealed that radon-based values exceeded hydrodynamic calculations in several areas, and vegetation emerged as a potential control on 222Rn behaviour. Conservative estimates derived from Darcy's calculations indicate that approximately 15% of total available freshwater is lost to the sea via SGD. These findings underscore the need to incorporate fSGD into coastal freshwater assessments and to further investigate ecohydrogeological processes influencing SGD under increasing climatic and anthropogenic stress.
Keywords:
hydrological cycle
Radon-222
sand-dune barrier
submarine groundwater discharge
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2.9
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