## 6 Discussion
### The Conceptual Model  
All data collected, elaborated, and analyzed may be resumed in a conceptual model for CO\({}_{2}\) degassing in the AVGA and may be useful in better defining the implications of the interplay of processes of natural degassing and the effects of the superposition of electricity production. Figure 11 shows a 3D sketch of the Piancastagnaio geothermal field and the Bagni San Filippo greenfield geothermal system, which can be used to easily visualize the observed processes of formation, transport, and release on the surface of the Earth in the AVGA. Our data suggest that from a statistical point of view, CO\({}_{2}\) is mainly of deep origin with a contribution because of the biological activity of soils and plants. Deep CO\({}_{2}\) derives by the contribution of the mantle, deep magmatic systems and by the thermometamorphic processes acting at shallow depths at the interface between granites and its wall rocks where thick layers of corpubianites form. The granite depth is revealed by the K-horizon reflector (the deep roots of the AVGA geothermal system). The CO\({}_{2}\) from this source is preferentially transported upwards by the convective systems developed inside the water-dominated deep fractured geothermal reservoir hosted in thermometamorphic phyllites. From this geothermal deep reservoir, gases rise upward to feed the shallow geothermal reservoir hosted in porous fractured carbonate-evaporitic rocks. The convection of the high temperature, aqueous fluids in reservoirs, and tectonic traps induce the formation of NCG (non-condensable gases) gas and vapor accumulations at the reservoir top because of the permeability contrast with the overlying clay-rich impermeable cover formation. The impermeable cover of geothermal systems stops rising up of the aqueous fluid, but it is not impermeable to gas, thus allowing the gas to rise to the surface and fueling the widespread CO\({}_{2}\) diffuse emissions that characterize this area. In the presence of tectonic breaks (faults \begin{table}
\begin{tabular}{c c c c c} \hline \multirow{2}{*}{**Diffuse Degassing Area**} & **Diffuse CO\({}_{2}\) Degassing** & **Diffuse CO\({}_{2}\) Degassing** & **GPPs** & **Sum** \\  & **(biological Component)** & **(Deep Component)** & **(t/d km\({}^{2}\))** & **(t/d km\({}^{2}\))** \\  & **(t/d km\({}^{2}\))** & **(t/d km\({}^{2}\))** & **(t/d km\({}^{2}\))** \\ \hline Piancastagnaio (24.8 km\({}^{2}\)) & & & & \\ (brownfield) & 19 & 59 & 31 & 109 \\ Bagnore (14.5 km\({}^{2}\)) & 18 & 44 & 45 & 107 \\ (brownfield) & & & & \\ Bagni San Filippo (12.3 km\({}^{2}\)) & & & & \\ (greenfield) & & & & \\ Paglia Valley (7.13 km\({}^{2}\)) & 19 & 84 & - & 103 \\ (greenfield) & & & & \\ \hline \end{tabular}
\end{table} 
Table 8: Areal normalized natural and GPPs CO\({}_{2}\) fluxes, greenfields, and brownfields. GPPs calculated based on data from [13]. and fractures) in impermeable subsoil formations or the absence of impermeable formations at the top of geothermal reservoirs, concentrated gas emissions, i.e., gas vents, occur. The analysis of the natural CO\({}_{2}\) flux from soil and concentrated emissions (gas vents, active fault systems, mining areas, and GPPs' emissions) highlights that a total CO\({}_{2}\) emission of 17,934 t/d occurs in the AVGA. The comparison with the emissions from the GPPs (1418 t/d) show that only 7.9% of the total carbon flux was issued by GPPs. Consequently, the performed survey for this whole geothermal area of Italy can define the true ratio between the natural emissions from the crust to the atmosphere occurring in this area and the emissions measured in GPPs. We demonstrate first the low contribution of geothermal energy production to increase the contribution of CO\({}_{2}\) emissions to the atmosphere.