Submarine springs in the Gulf of Taranto (Italy): geology, hydrogeology and cave diving explorations

In coastal karst lands, due to difference in permeability among contiguous strata, emergence of springs may occur inland or as submarine springs, as in the Gulf of Taranto (Italy), marking the S limit of Murge, the largest karst sub-region in Apulia. Groundwater from N-NW feed some inland springs, sometimes originating small rivers, with Tara as the main significant. In addition to surface waters, submarine springs are present within the gulf, namely in Mar Piccolo of Taranto, an over 20 km² wide basin (10-14m depth) consisting of two bays with elliptical shape, connected through a channel. In the N sectors of the bays 34 submarine springs have been identified. Locally called citri, a word of Greek origin, deriving from history of Taranto (founded as a Greek colony), they work as thermal regulators for the water temperature, allowing extensive development of mussel farming. The groundwater emission sites are characterized by funnel-shaped morphology with a circular profile at the sea surface. In the past, attempts were done to tap these waters (Cotecchia et al., 1990), but technical and engineering problems, brought to abandon such activities.

In the Murge district the Cretaceous limestone aquifer is covered by Plio-Pleistocene calcarenites, clays and terraced marine deposits, with secondary porous aquifers flowing within these latter. Origin of the citri is related to surface dismantling and erosion of the cover, and to emergence of the confined water hosted in the limestones. In most of the cases, it comes out in wide areas, without a clear karst conduit. Among the few caves explorable by man, there is Citro Galeso, at the W bay: with a diameter of 20 m, and 18m depth, it has discharge of 0,750 m³/s.

Inventoried since the first half of the XX century (Cerruti, 1938), only recently the distribution of citri was studied in detail (Valenzano et al., 2018). The largest spring (Saint Cataldo’s eyes) is located just outside the two bays, in Mar Grande: 200x300 m-wide, it consists of two cavities, reaching depth of 48 and 52 m, respectively, below sea level, and deepening for 20 additional meters.

To improve the hydrogeological knowledge of the area, we are carrying out a variety of scientific activities, starting from exploration and surveying of accessible springs. A significant role is being attributed to the study of the cave systems, as regard their distribution and pattern network. As outflow yield and flow velocity data are not yet available for all citri, some measurements will be done at this aim. In addition, water samplings will be taken for characterizing the chemical constituents, and for assessing the presence and nature of pollutants.

 

References

Cerruti A., 1938, Le sorgenti sottomarine (Citri) del Mar Grande e Mar Piccolo di Taranto. Ann. Ist. Sup. Navale, Napoli, 7.

Cotecchia et al., 1990, Hydrogeological conditions and field monitoring of Galeso submarine spring in the Mar Piccolo of Taranto (southern Italy). Proc. 11^th SWIM, 171-208.

Valenzano et al., 2018, Holocene Morpho-sedimentary evolution of Mar Piccolo basin (Taranto, Southern Italy). Geogr. Fis. Dinam. Quat., 41, 119-135.