Integration of surface and subsurface data for the understanding of karst hydrogeology: caves as open windows to the water table

Karst groundwaters are the main hydric supply in many countries of the world (Stevanovic, 2015), and represent a precious resource to be protected and properly managed. They are extremely vulnerable to pollution (Goldscheider & Drew, 2007; Ford & Williams, 2007; Parise & Gunn, 2007), since karst landforms such as sinkholes are the preferential sites for pollutants entry, putting in direct contact the surface with the vadose zone. Marine intrusion has to be added in coastal areas as a further source of contamination for water quality (Masciopinto et al., 2017), locally with significant impact on society. A good knowledge of the geological and hydrogeological features, obtained through collection of lithological, petrographic, structural, geomorphological and hydrogeological data, is the necessary starting point to plan and develop the best practices and actions toward protection of underground water resources. In karst, this can be reached through integration of traditional geological approaches at the surface with direct exploration and surveying within the caves, by means of speleological techniques (Liso et al., 2019, 2020; Parise et al., 2020). In Apulia, one of the more extensive karst areas in the Mediterranean Basin, freshwater resources are stored within the fractured and karstified limestones making up the backbone of the region (Maggiore & Pagliarulo, 2004; Cotecchia, 2014; Liso & Parise, 2020). However, in contrast with the high number of surface sinkholes, dolines and poljes distributed over the Apulian karst landscape, among the over 2000 caves registered in the Regional Inventory, only two directly reach the water table. They are therefore a sort of open windows to the water table, ideal sites where to study hydrogeology. In this contribution we present our efforts, performed through direct explorations and in cooperation with cavers, to combine surface/subsurface data to enrich the available information about hydrogeology of Apulian karst systems, and to contribute to a better understanding of its main features.