## 3 Results
### Characterization of Soluble Ions  
The results of the determination of anions and cations, expressed as w% (percentage of weight of each ion with respect to the total dry mass of the sample), are listed in Table 2.  
The percentage of soluble ions in the samples exhibited significant variation, with an average of 20% and maximum and minimum values of 70% and 3.1%, respectively, for S\({}_{3}\) and S\({}_{\text{6b}}\). The composition of the samples also demonstrated considerable heterogeneity. The sum of SO\({}_{4}\)\({}^{2-}\) and Ca\({}^{2+}\) (calcium) in numerous samples represented the major components of soluble ions, up to 97% for S\({}_{3}\) and S\({}_{11}\). The average concentration of calcium was 7.2%, ranging from 0.65% to 22% in S\({}_{\text{4a}}\) and S\({}_{3}\), respectively. SO\({}_{4}\)\({}^{2-}\) showed an average concentration of 11% with a maximum in S\({}_{3}\) (47%) and a minimum of 0.19% (S\({}_{1}\)). Cl\({}^{-}\) was present in all samples with an average of 1.0%, ranging from 2.7% to 0.18%, observed in S6a and S11, respectively. Na\({}^{+}\) was also present in all samples, with an average of 0.35%, ranging from 0.090 to 0.83% observed in S10 and S\({}_{\text{4a}}\), respectively. NO\({}_{2}\)\({}^{-}\) was present in only two samples: S\({}_{8}\) and S\({}_{11}\). NO\({}_{3}\)\({}^{-}\) was present in all samples with an average of 0.23%, ranging from 0.81% to 0.093%, observed for S\({}_{1}\) and S\({}_{\text{6b}}\), respectively. The concentrations of Mg\({}^{2+}\) and K\({}^{+}\) were notably low in all samples, as were the concentrations of C\({}_{2}\)O\({}_{4}\)\({}^{2-}\) and PO\({}_{4}\)\({}^{3-}\). The concentration of oxalate was extremely low, and it was not detected in all samples. The highest level was found at  
Figure 5: Raman spectra of (**A**) cultures from the isolated colonies (S\({}_{\text{6a}}\)) (3) and (5) and S\({}_{11}\); (**B**) sample of the substrate with evidence of biological colonization (S\({}_{\text{6a}}\), S\({}_{\text{5a}}\), S\({}_{\text{7}}\)) (C = calcite; G = gypsum; P = polysaccharide compounds). sample point S9, measuring 0.056%. F\({}^{-}\) was present only in five sampling points (S\({}_{7}\)-S\({}_{11}\)) with a maximum in S\({}_{9}\) (0.69%). The results of the determination of anions and cations were converted to \(\upmu\)Eq to establish the ionic balance (Figure 6a). Ioni c balance was calculated by subtracting the total quantity of cations from the total quantity of anions, all measured in \(\upmu\)Eq. A negative balance indicates a deficiency in one or more anions, that may not have been analyzed. Assuming electro-neutrality in the solution, this deficiency was attributed to unmeasured carbonate and bicarbonate [67]. The presence of carbonate as calcite was also detected by Raman analysis. The graph presented in Figure 6b demonstrates that the trends of calcium and sulphate are perfectly synchronized across all samples examined, suggesting that calcium sulphate (CaSO\({}_{4}\), gypsum) was the primary component of the samples, as reported in other studies [68]. Furthermore, a comparison between sodium and chloride ions revealed a strong correlation (Figure 6c). The analysis performed on a sample of pure salt efflorescence (labelled Ss) indicated that the sample was primarily composed of sodium and sulphate, thereby identified as Na\({}_{2}\)SO\({}_{4}\) (sodium sulphate). This salt exists in two primary forms: thenardite (Na\({}_{2}\)SO\({}_{4}\)) and mirabilite (Na\({}_{2}\)SO\({}_{4}\)\(\cdot\)10H\({}_{2}\)O). Under specific environmental conditions [69], the latter undergoes a volume increase of up to 400% [70], potentially leading to material damage. \begin{table}