CARBON-DIOXIDE EMISSIONS AT AN ITALIAN MINERAL SPRING - MEASUREMENTS OF AVERAGE CO2 CONCENTRATION AND AIR-TEMPERATURE

Emissions of carbon dioxide from vents at the Bossoleto mineral spring in Central Italy have been calculated to exceed 12 t day(-1), This emission leads to enhanced atmospheric concentrations of CO2 over an area of more than 3000 m(2). The vent gas is over 99% pure CO2, with a characteristic isotopic signature that is totally depleted in C-14. At night, concentrations at the bottom of the bowl-like depression can increase to levels approaching 75%. In the morning, this high concentration of CO2 is associated with a rapid temperature increase of over 10 degrees C before the CO2 disperses. This site is being used in a number of studies of the response of plant communities to long-term enhanced CO2 concentrations. The problem of defining CO2 concentrations in these studies was approached by comparing estimates determined by gas analysis measurements and isotopic analysis of leaf material, The isotopic method used C-14 as a tracer, integrating effective concentration over the life of a leaf by calculating from the ratio of C-14 measurements of plant material growing near the spring and at a control site. The estimates obtained using isotopic analysis of leaf material were similar to gas analysis measurements obtained during the day. This suggests that plants at this site are responding to the concentrations during the day, rather than the much higher night-time concentrations, making the system useful for biological research.