## 3 Results and Discussion
### Correlation between the Analyzed Parameters  
As pointed out in previous research, some of the parameters investigated may be related to each other, and their values may be a function of the characteristics of the sampling site. For example, a correlation was found between the concentration of all or some of the heavy metals detected and the grain size distribution function of the point of origin of the sampled material [32]. Therefore, based on this hypothesis, the present study investigates, using statistical tests, whether the values of the detected heavy metals can be related to the characteristics of the sampling station, especially grain size distribution and land use.  
Since the analyses carried out with the Shapiro-Wilk test have shown a normal distribution of the data, [PERSON]'s test was used to verify the homogeneity of the variances, obtaining both homogeneous and non-homogeneous sample variances. Therefore, it became necessary to use two different tests to check if the null hypothesis could be rejected, i.e., the Student T-test and the Mann-Whitney test.  
From the analyses carried out, it emerges that, concerning the sediments from the San Giuliano reservoir (Table 11), the Shapiro-Wilk test returned a \(p\)-value greater than 0.05. Therefore, it is possible to accept the null hypothesis, according to which the data follow a normal distribution. Subsequently, the application of [PERSON]'s test to both data vectors shows that the \(p\)-value is more significant than 0.05 (variances are homogeneous), except for Arsenic. Therefore, for all parameters, [PERSON]'s T-test was performed; in contrast, for Arsenic alone, the non-parametric Mann-Whitney test was used, to compare the averages of two groups of samples extracted from two populations with homogeneous or non-homogeneous sample variances.  
In this study, the null hypothesis H\({}_{0}\) to be tested is that the distribution of heavy metals is not influenced by the sampling position within the catchment area; since this is considered acceptable as the \(p\)-value \(p\) > 0.05, it can be said to be verified for most parameters. This is not true, however, for Be, Cr and Ni (\(p\) < 0.05, in red), for which it is necessary to accept the alternative hypothesis H\({}_{1}\), i.e., the concentration of these elements is influenced by the sampling point and site characteristics.  
For the sediments sampled at the Camastra reservoir, the statistical analyses (Table 12) results show that the data follow a normal distribution (the null hypothesis is verified) since the \(p\)-value obtained from the Shapiro-Wilk test is more significant than 0.05. [PERSON]'s test, on the other hand, shows that, for most of the parameters considered, the variances are homogeneous (\(p\)-value > 0.05), and for these, the Student's T-test was performed. For Chromium, Thallium, and Vanadium only, the \(p\)-value resulting from [PERSON]'s test is less than 0.05; for these parameters, the non-parametric Mann-Whitney test was used to check the acceptability or otherwise of the null hypothesis.  
The analysis of the data in Table 12 shows that for all parameters, the null hypothesis H\({}_{0}\) can be accepted (the position within the catchment area does not influence the distribution of heavy metals); therefore, for the Camastra sediments, the concentration of these elements is not influenced by the sampling point and site characteristics.