Dripping and underground river waters shed light on the ecohydrology of a show cave

Water and air flows connect underground ecosystems to the surface, affecting the cave chemical and physical properties. Together with the visitor's fluxes in show caves and occasional presence of cavers in wild caves—excluding the large amounts of organic supply by bat or bird colonies or large sinking rivers bringing vegetal debris—fluid flows are the main means of transport of nutrients into the normally oligotrophic cave environment. The aim of this work was to investigate the chemical characteristics of waters in the Pertosa-Auletta Cave (Italy), focusing on drip water and on the underground Negro river, seasonally and in different areas of the cave. In particular, three trails with different environmental characteristics and tourism pressure were investigated in order to shed light on the processes affecting the ecological equilibrium of the hypogean ecosystem. Dripping and flowing river waters, both rich in Ca because of their interaction with carbonate rocks, show distinct chemical signatures regarding the other chemical elements (especially K and Mg) due to lithological and hydro-dynamical differences. Moreover, water chemistry is affected by the seasonality in the pluviometric regime owing to the subsequent variability in the dilution effect. Bat colonies, dwelling mainly along the fossil trail, enrich dripping waters with P and N. Their concentrations have also been found at fairly high values across the whole trail network, suggesting an additional potential role of leaching from agricultural and forested soils above the Pertosa-Auletta Cave in defining dripwater chemistry.