## 3 Results
### Partial Dependence Plots  
The previous results helped understand the importance of the categorical F.G. in the determination of the metal pollution potential. To understand the effect of individual MIV belonging to the respective F.G., partial dependence plots (PDP) are an effective way to visualize the relationship between dependent and independent variables in a model. Figure 4 shows the partial dependence plots for the variables of the meta group C1. Even though they are in the same group, the two metals have differing, often even opposing, relationships with the same MIV. The mean EVI of the drainage area above the sample location strongly affects Al in (a). In values higher than 2000, there is an increasing probability of classification as L.V. This shows a potential relationship between the size and health of the vegetation cover and Al mobilization and transport processes. The metal As shows some changes along the \(x\)-axis but no clear trend. The graph shows contrary relationships for both metals for lithological SiO\({}_{2}\) in (b), the basin's geology's estimated accumulated lithological SiO\({}_{2}\) content. From 0% to 40%, Al increases while As decreases; from then on to higher SiO\({}_{2}\) values As increases while Al decreases until 70%. Similar opposing behavior can be seen in plots (d), (e), and especially in (c), which shows a perfect opposite reaction to changes in the sulfur content in the surface rocks of the basin. In Figure 5, the PDP for the meta-group C2 is presented. There is a general similarity between the trends of the different lines in many of the plots. In (a), the mean accumulated percentage of lithological K\({}_{2}\)O content of the rocks in the basin shows a decreasing probability of L.V. for all three metals. The annual runoff in 1999 in (b) shows some deviations, but in general, the trend for the whole group is negative with increasing runoff. The plots (d) and (f) show similar behavior of the curves, while in e) the linear trend of the curves is the same. In (e) and (g), Co and V show an opposing behavior. The plots for C3 in Figure 6 show both similarities and differences between the effects of the MIV on the metals in this group. In plot (a), the relationship with the percentage of surface imperviousness in the basin in the year 2001 is similar for Cd, Cu, Pb, Sn, and Zn. The probability of a L.V. generally decreases with an increasing imperviousness. A higher percentage of impervious surfaces indicates a larger presence of human-built structures, such as roads and cities. Pb and Zn show a curve where medium imperviousness values are associated with the lowest probability. It increases in the higher imperviousness range. In plot (b), which shows the relationship with the sum of years since the construction of all dams in the basin that are of the construction type Gravity, it is visible that L.V. of Cd and Pb has a positive relationship with this parameter up until 4000 after which there is little change. At the same time, Cu, Sn, and Zn decrease with increasing values up until 4000, after which they show little change as well. This difference between the effects on  
Figure 3: Display of the multidimensional space. The number of MIV per F.G. defines the position of each metal. The background colors indicate the area belonging to the respective clusters. The symbols of the individual points indicate allocation to one of the four meta groups (clusters) C1–C4. the metals is also visible in plot (d), which shows the total storage of all dams of type Rockfill in the basin. Here again, Cd and Pb behave differently from the other three metals. The differing effects of the reservoirs may indicate the dissimilar importance of reservoir effects on these metals. In (f) and (h), all five metals behave similarly with a decreasing linear trend of the probability with increasing impervious surface near rivers and woody wetlands cover, respectively. Figure 4: PDP plots for group C1. The \(x\)-axis represents a MIV, the \(y\)-axis represents the associated probability of a L.V.