Use of the Radiocarbon Activity Deficit in Vegetation as a Sensor of CO 2 Soil Degassing: Example from La Solfatara (Naples, Southern Italy)

Soil CO 2 flux measurement is a key method that can be used to monitor the hazards in an active volcanic area. In order to determine accurately the variations of the CO 2 soil emission we propose an approach based on the radiocarbon ( 14 C) deficiency recorded in the plants grown in and around the Solfatara (Naples, Italy). We twice sampled selected poaceae plants in 17 defined sites around the Solfatara volcano. 14 C measurements by liquid scintillation counting (LSC) were achieved on the grass samples. The 14 C deficiency determined in the sampled plants, compared to the atmosphere 14 C activity, ranged from 6.6 to 51.6%. We then compared the proportion of magmatic CO 2 inferred to the instantaneous measurements of CO 2 fluxes from soil performed by the accumulation chamber CO 2 degassing measurement at the moment of the sampling at each site. The results show a clear correlation (r=0.88) between soil CO 2 fluxes and 14 C activity. The determination of the plants 14 C deficiency provides an estimate of the CO 2 rate within a few square meters, integrating CO 2 soil degassing variations and meteorological incidences over a few months. It can therefore become an efficient bio-sensor and can be used as a proxy to cartography of the soil CO 2 and to determine its variations through time