Bridging Land and Sea: Geophysical insights into coastal karstic groundwater dynamics, freshwater plumes and saltwater intrusions in the urban regions of Antalya (Türkiye)

This study investigates the on- and offshore fresh to saline groundwater distribution as well as the submarine groundwater discharge within a coastal karstic aquifer system in Antalya (Türkiye). Groundwater acts as a critical link between on- and offshore environments, connecting freshwater systems to the saline oceans. With an increasing population along coastlines, understanding coastal groundwater interactions is essential. In this study we utilize on- and offshore hydrogeophysical techniques to image variations in subsurface porewater salinities. Offshore continuous resistivity profiling and hydroacoustic measurements are complemented by land based electromagnetic measurements. Our findings show how groundwater discharges into the sea through coastal and submarine freshwater springs while simultaneously facing the risk of saltwater intrusions nearby. Diffuse groundwater flow dominates along the main beach area of Antalya, while channelized flow occurs primarily along the cliff coastline where submarine springs occur. The springs create distinct salinity anomalies in the water column and remove the sediment cover from the carbonate aquifer, exposing hard rock on the seafloor and creating different habitats. The multi-method geophysical approach provides a detailed picture of freshwater-saltwater interactions and highlights regions of varying groundwater discharge into the sea. Our findings contribute valuable insights for water management strategies in Antalya, with implications for safeguarding freshwater resources and mitigating the risk of saltwater intrusions. • Submarine groundwater discharge occurs in close proximity to potential saltwater intrusions. • Diffuse and channelized SGD are imaged with resistivity and hydroacoustic methods. • Submarine springs remove sediment from the bedrock, creating new habitats on the seafloor.