Microclimatic characterization of a karstic cave: human impact on microenvironmental parameters of a prehistoric rock art cave (Candamo Cave, northern Spain)

Abstract

The Candamo Cave contains an impor- tant group of paleolithic paintings which have been seriously deteriorated due to mass tourism. In this work, an analysis was carried out of different cli- matic parameters (CO2, temperature, humidity, 222 Rn) during annual cycles with the cave closed to the public and during an experimental period of controlled visits. The effect of visits on the geo- chemical characteristics of karstic water was also analyzed together with the cave ventilation. The natural variations in the cave air CO2 were above 3000 ppm, the increase produced through visits was only 100-110 ppm and since the humidi- ty is almost permanently at saturation point, the critical parameter which limits the visitor capacity becomes air temperature. The temperature changes during the annual cycle are of the order of 1 7C in the external part and less than 0.5 7C in the internal part of the cave and a maximum increase of 0.13 7C was observed during the period of the visits. The 222 Rn and CO2 concentration minimums in the summer period (July-October) show that this is the most propitious time for visits, since the greatest ventilation is produced in the cave at this time and, therefore, the greatest capacity for recovery. The geochemistry of the water, on the other hand, indi- cated that this is the period of the year in which processes of wall corrosion can be most easily in- troduced, although this would be of limited magni- tude. The visitor capacity calculated was 29 visi- tors/day.