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 em ission leads to enhanced atmospheric concentrations of CO2 over an are a of more than 3000 m(2). The vent gas is over 99% pure CO2, with a ch aracteristic isotopic signature that is totally depleted in C-14. At n ight, concentrations at the bottom of the bowl-like depression can inc rease to levels approaching 75%. In the morning, this high concentrati on of CO2 is associated with a rapid temperature increase of over 10 d egrees 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 the se studies was approached by comparing estimates determined by gas ana lysis measurements and isotopic analysis of leaf material, The isotopi c method used C-14 as a tracer, integrating effective concentration ov er the life of a leaf by calculating from the ratio of C-14 measuremen ts of plant material growing near the spring and at a control site. Th e estimates obtained using isotopic analysis of leaf material were sim ilar to gas analysis measurements obtained during the day. This sugges ts that plants at this site are responding to the concentrations durin g the day, rather than the much higher night-time concentrations, maki ng the system useful for biological research.