Environmental pressures on conserving cave speleothems: effects of changing surface land use and increased cave tourism

Speleothems (stalagmites, stalactites, etc.) have long drawn visitors underground to visit limestone caves throughout Europe, and since the start of the twentieth century many public show-caves have been established. For example, in the British Isles today there are over 20 show-caves; the most visited may receive in excess of 500 000 visitors annually. Recent research has highlighted the potential destructive influence of visitors to caves by the effects of respiration, which can generate elevated CO2concentrations, and by their heating effect, which can raise temperatures by up to 3°C. Values of up to 5000 ppm of CO2have been reported in both private and public caves, but with clear evidence that the passage of visitors through the cave system causes increases of up to 200%. It has been suggested that such elevated CO2may cause the destruction of speleothems within the caves, as increased CO2leads to a higher equilibrium concentration of calcium within the drip waters feeding the speleothems, and hence causes dissolution of existing features, although it has to be noted that there is a significant natural variability of cave air CO2and it is against this that the anthropogenic effects of visitors has to be judged. Data are presented here for both cave air CO2concentration and temperature, as well as a third variable, that of the drip-water calcium concentration, which is also a key determinant of speleothem growth and may be affected by surface land use changes. It is demonstrated that cave speleothems may be at risk from the increased passage of tourists, but that this risk is highest in caves where ventilation is poor and where either the calcium ion concentration of the drip waters is low (<2·0 mmol l−1) or where there have been or are likely to be significant changes in surface land use, which decrease the drip-water calcium concentrations and hence make corrosion more likely.1998 Academic Press Limited