The impact of visitors on the microclimate of Italian touristic show caves

The cave microclimate is one of the elements, of the karst ecosystem, that can be taken into account for monitoring the spatial and temporal evolution of the underground atmosphere and hydrosphere. In the last decades, the available technology has permitted to gather many atmospheric physical parameters useful to characterize the spatial and temporal evolutions of the underground microclimate and eventually to prevent and manage possible irreversible modifications. Several yearly time series of underground atmospheric parameters, collected from the main Italian show caves from Antro del Corchia in the Apuane Alps to Grotta di Monte Cucco and Grotta Grande del Vento- Frasassi in Central Italy are compared. These caves develop for many kilometres and present a complex morphological pattern with several entrances located at different altitudes. The thermal variations of the underground atmosphere induced by the visitors, in general, reach a maximum few °C and are noticeable until some tens of meters from the touristic trail. They are of short duration and don’t succeed to modify the trend over a long period. They follow daily cycles and these variations are compatible with the recovery capacity of the hypogean systems. The airflow across the entrances of the karst systems is mainly controlled by the value of the outside temperature connects to the seasonal variations and day/night cycles. In the studied caves, the airflow is quite complex and however influence only slightly by the presence of the visitors and mainly by the air flux due to the opening of the doors of the artificial tunnels where present. In all cases, the air flows exchanges can reach a discharge of many cubic meters/sec. The evolution of the concentration of the CO2 in the tourist part of the caves varies by a few hundred ppm, due to the presence of the visitors. The natural variations reach one order of superior magnitude. The opening of the doors of the artificial tunnels and the flow of the outside air tends to dilute the concentration of the C02 both during the day and for more long trend. However, these karst system seems enough capable to absorb the thermal perturbations and CO2 increase, restoring and maintaining the pre-existent environmental conditions. The recovery time is controlled by the inertia of the system where the airflow and the hydrogeological condition play an important role. The energetic budget in the underground system seems to be due to an input of about 80% from electric power and the warmth of the visitors which are dissipated by 70% by the air circulation and 20% at the interface air/water/ rock. Despite these decades of time-series data on the underground caves, these observations do not enough do not answer for to long term effect on the hypogean ecosystem