Basins that fill from below
The Gargano Promontory, the "spur" of the Italian boot, is a classic karst landscape, a terrain formed from the dissolution of soluble rocks. The region's backbone is a thick sequence of Upper Jurassic to Lower Cretaceous shallow-water carbonates. Over millions of years, water has sculpted this limestone, creating a network of underground conduits and surface depressions known as dolines.
These seasonal flood basins are a peculiar and fascinating feature of this environment. Locally known as "cutini" or "pantanelle," they are not conventional ponds filled by rainwater running off the surface. Instead, they fill from the bottom up. The entire peninsula sits on an underground aquifer contained within the porous Cretaceous limestone. During the wetter winter and spring months, the water table within this aquifer rises. In locations where the floor of a doline is sealed by a layer of impermeable clay—typically reddish "terra rossa" soils—the groundwater emerges on the surface, creating a temporary lake. These ephemeral wetlands exist for a few months before the water level in the aquifer drops, and the lakes drain away through sinkholes, known as ponors, leaving behind a dry, flat basin for the summer.
One of the largest and most spectacular examples of these karst depressions in the region is the Dolina Pozzatina, near San Nicandro Garganico. It measures over 1,800 meters in upper circumference and has a depth of more than 130 meters. It doesn't typically flood entirely, its formation is a direct result of the same karst processes of collapse and dissolution that shape the smaller, seasonal basins.
Ephemeral oases of life
The cyclical flooding and drying of these basins create a habitat recognized by the European Union as a priority for conservation. This environment supports a specialized collection of flora and fauna that have adapted to the extreme seasonal changes. The vegetation is dominated by therophytes (annuals) and geophytes (plants with underground bulbs or tubers), which can survive the dry summer months as seeds or dormant organs. Plant species from the genus Isoetes (quillworts) are characteristic of these Mediterranean temporary ponds.
When the basins fill with water, they burst with life. The dry sediment contains the dormant eggs of various aquatic invertebrates. Among the most notable are anostracans, or fairy shrimp. These small crustaceans, such as Chirocephalus diaphanus, have desiccation-resistant cysts that can lie dormant for years, waiting for the return of water to hatch, mature, and reproduce within a few short weeks. The fauna also includes a variety of insects, amphibians, and other micro-invertebrates that have evolved to exploit these fleeting aquatic ecosystems. This specialized biodiversity makes the temporary ponds of Gargano important areas for conservation within the broader area of the Gargano National Park.