## 6 Discussion
### The Conceptual Model
In general, this represents the first important improvement of the existing knowledge about the GPPs' CO\({}_{2}\) emissions and demonstrates the importance of defining the natural emissions in the geothermal areas for a better understanding of the true role of GPPs in greenhouse gas emissions. This topic is further discussed in the following points. Figure 11: Conceptual model exemplified in a section crossing the Piancastagnaio geothermal field and the undisturbed Bagni San Filippo area (Icons designed by macrovector/Freepik). Four diffuse high emission areas with very high values of natural gas fluxes from the soil were discovered and areal bounded. These areas mainly coincide with AVGA geothermal/hydrothermal systems in which convective processes are strongly active. The CO\({}_{2}\) that forms in the thermometamorphic aureole of the magma chamber/intrusions of the Mt. Amiata volcano, in the deeper portions of the magmatic system, and rising from the mantle is preferentially transported upward in water-dominated geothermal convection cells formed in the shallow and deep geothermal reservoirs. Data analysis for these four areas shows that the global CO\({}_{2}\) flux, natural plus power plants flux, is similar between the areas. The CO\({}_{2}\) flux stands at 103-115 t/d km\({}^{2}\). Two of the areas coincide with the upflow areas of the Bagnore and Piancastagnaio geothermal fields and have been in operation for 60 years (brownfields), while two areas are located in areas not in operation for geothermal production (greenfields). The highest emissions are observed in the Bagni San Filippo area and are diffuse and concentrated (in faults, water thermal pools natural manifestations, gas vents, and in correspondence with disused Hg mining sites) and in the Paglia River area. The comparison between the geothermal and the latter areas highlights that the total flow (t/d km\({}^{2}\)) is practically coinciding around a mean value of 110 t/d km\({}^{2}\), if the GPPs emission is included in the budget, while the diffuse natural flow in geothermal areas is much lower. In the Bagnore area, it slightly exceeds 55% of the total flow, while it is higher than 70% of the total flow in Piancastagnaio. These experimental data indicate very high gas soil diffuse and concentrate emissions in the AVGA, which are relatively constant in the various sectors of the volcanic geothermal district. This is possibly because of the occurrence of a relatively homogeneous process of CO\({}_{2}\) generation at depth over a roughly circular area mainly coinciding with the deep roots of the AVGA feeding system (magma chamber/intrusions and related thermometamorphic halo and more in the general volcano plumbing system). In this framework, in the areas of geothermal fields, the survey shows that the diffuse natural emissions of gas markedly decrease. If we add the emissions from the area of power plants (calculated on the reservoir area in operation) to the soil diffuse emissions of the same area, a good match is observed with those of the undisturbed (greenfield) areas of Bagni San Filippo and Paglia. These data indicate that the gas emissions linked to the operation of power plants substantially balances the natural gas soil flux that appears markedly reduced in operation areas. The values of CO\({}_{2}\) emissions of Bagnore GPPs normalized to the reservoir area, 45 t/d km\({}^{2}\), summed to deep and background CO\({}_{2}\) for the same area, 109 t/d km\({}^{2}\), are equal to the mean values of the undisturbed areas (110 t/d km\({}^{2}\)). The same value is obtained for the Piancastagnaio area.