Geomorphological and hydrogeological features of submerged coastal sinkholes in the Apulian karst

Low coastal karst is often characterized by widespread presence of sinkholes flooded by mixing of fresh and salt water. Such a mixture creates peculiar environments and ecosystems, at the same time predisposing the areas to possible hazards, in the form of formation of new sinkholes, or enlargement and coalescence of the existing ones through failures at their rims. This is definitely the situation for the south-western coast of Salento (Apulia, southern Italy), where the local karst setting is dominated at the surface by presence of flooded sinkholes, and by bays and inlets of circular shape along the coast. These latter are typically the result of coalescing processes of original individual sinkholes, which outer rim is eventually broken by the action of sea waves. Such a situation characterizes actually many other sites in the region, not only limited to the Ionian side but also involving the Adriatic coastine of Apulia, to the east (Liso & Parise, 2023). In the coastal stretch extending from Torre Castiglione to Palude del Capitano, we have started a variety of activities, with further more on the way: among these, mapping of the sinkholes and interpretation of their mechanisms of formation, both along the coast and inland; identification of the main structural lineations, and of the likely control they exert on sinkhole development and evolution; monitoring of the physico-chemical parameters of the waters, with particular focus on those where upwelling of sulphureous waters has been observed; evaluation of the dissolution rate of carbonate rocks within the submerged areas; assessment of the sinkhole hazard, also in relation to the widespread presence of tourist sites, highly frequented during the summer season. Comprehension of the main flowpath of groundwater, from the inland areas toward the coast, is one of the main goals of our research, which is part of a wider project addressed also to evaluate the biological aspects in these peculiar, high biodiversity, ecosystems.