## 3 Results and Discussion
### Seasonal Changes in the Distribution of the SOM Clusters  
As previously stated, it is possible to know to which neuron is associated with each well. Since the season and year associated with each sample is also known and specified, it was also possible to detect the occurrence of seasonal changes in water types or within water types through time, after evaluating the presence of the different wells in a specific neuron or cluster. A similar approach was previously undertaken by [9] to evaluate spatio-seasonal hydrogeochemical changes in groundwaters from the Red River Delta in Vietnam. After superimposing the location of the wells with the piezometric level recorded during the dry season of 2002 by [14] (Figure 10) it can be seen that the wells located in the areas where the hydraulic head is below the mean sea level (dashed red lines) were systematically assigned to cluster C2 after 2016. As previously mentioned, C2 was characterized by higher concentrations of Na\({}^{+}\), Ca\({}^{2+}\) and Cl\({}^{-}\) as well as lower concentrations of HCO\({}_{3}\)\({}^{-}\), typical of more saline waters (Table 1, provided in Appendix A). Table 1 summarizes the positioning of all 18 wells within the SOM map during the 6 years analyzed. Figure 10: Location of the sampling wells superimposed to the hydraulic head recorded in 2002 according to [14]. The fact that after 2016, there was a shift to more saline waters in two wells very distant to the shore and, apparently not affected by a lowering of the phreatic level (P093 and P111) is of particular concern. Both wells were clustered in C1 from 2010 to 2013, a cluster characterizing samples with a more intermediate groundwater composition and significantly less mineralized than waters included in C2. This situation could be reflecting two phenomena: (i) diminution of the amount of recharge waters received and (ii) increased extraction of water that leads to a lowering of the piezometric level. Both phenomena are not mutually exclusive and could also be taking place simultaneously according to [2,16] for the Tuscany area in a climate change scenario a decrease in the amount and frequency of precipitation should be expected. The shift into a more arid climate would also lead to an increase in the influence of evapotranspiration over the groundwater level [30] increasing the concentrations of the ions in the waters that reach and recharge the groundwater. The visual evaluation of the changes in the phreatic level in areas near these wells (Bibbona for P093 and Cecina for P113) seems to support the above-mentioned hypothesis, since in both areas, from 2011 to 2018 a significant decrease in the phreatic surface is detected. This is particularly true in the Bibbona area, where the levels went from a range between \(-10\) to \(-12\) m to a range between \(-12\) to \(-14\) m (Figure A1, provided in Appendix A). The other 16 wells analyzed showed changes within the same cluster, moving to adjacent neurons depending on the season. As a general trend, wells moved towards neurons with lower concentrations of all ions (within the same cluster) during the wet season. This is thought to reflect the occurrence of a \"dilution effect\" during the wether and rainier season. All wells located at the south of the study area (P102, P104, P105, P106 and P531), were more susceptible to the above-mentioned effect, since there where near a recharge area (i.e., P102 and P531). In addition to this, these wells are all located in the area of Castagneto Carducci, which is characterized by the presence of silty-clayey facies alternated with gravel and conglomerate ones. Both lithologies are prevalent for at least the first 50 to 70 m and the clays and silts could be acting as a barrier that limits the mixing of the more mineralized waters from the northern area with the ones in the south, especially since according to [14] all the SSWBs present in the coastal area are to be considered as communicating due to the high density of water wells present.