Tracing groundwater recharge and contributions to perennial coastal wetlands in a semi-arid Chilean catchment using an integrated geochemical, isotopic, and groundwater dating approach

In the context of climate change and the increasing frequency of droughts, sustainable water resource management has become a major challenge worldwide, particularly in Mediterranean and arid regions such as central Chile. In systems strongly constrained by both climatic and anthropogenic pressures, understanding (i) recharge processes and (ii) groundwater-surface water partitioning in catchments and their associated sensitive coastal wetlands is essential for effective catchment-scale management.
This study aims to characterize the origin of freshwater within the semi-arid coastal Huaquén catchment and the associated perennial wetland located at its outlet to the Pacific Ocean. Fully distributed numerical models, calibrated at the regional scale, indicate significant inter-catchment groundwater flow, suggesting the contribution from deep and potentially old groundwater to the shallow aquifer and, consequently, to the coastal wetland. This hypothesis is tested using a multi-tracer approach applied to groundwater and surface water samples collected at multiple locations across the catchment.
The investigation integrates water geochemistry, strontium isotopes to identify source variations, stable water isotopes (δ¹⁸O) to constrain recharge and hydrological processes, chlorofluorocarbons (CFCs) as groundwater age tracers, and noble gases to identify recharge areas. By combining these tools, this study assesses the respective contributions of surface water, shallow groundwater, and deeper groundwater to the hydrological functioning of the catchment and the coastal wetland.