## 3 Results
### Trace Element Concentrations in Water  
The average trace element concentrations obtained in the present study vary from 2.46 ug/L for As to 141.63 ug/L for Pb. Based on the third (3 rd) quartile values, 75% of the trace element concentrations (in ug/L) are between 20.26 and 37.07 for Cd, 99.62-154.24 for Pb, 44.78-189.59 for Cr, 28.01-109.57 for Ni, 72.70-89.70 for Cu, 1.43-2.89 for As, 11.71-24.07 for Zn, and 10.95-31.73 for Mn (Table 3). These concentrations obtained for Ni, Pb, Cd, and Cr are higher than the WHO guidelines for drinking water (Table 3) [49,50]. It can be concluded that the waters from the hydrosystem are polluted by the trace elements Ni, Pb, Cd, and Cr and are not recommended for consumption. It should be noted that the Cr concentrations analyzed in this study are total and composed of the trivalent and hexavalent forms. Indeed, while trivalent Cr is essential for biological function at low concentrations, hexavalent Cr is very toxic at low concentrations. The ingestion of high concentrations of hexavalent Cr may cause dizziness, thirst, abdominal pain, hemorrhagic diarrhea, and in the most severe cases, coma and death. Hepatorenal syndrome, severe coagulopathy, or intravascular hemolysis may also occur. Carcinogenic effects following chronic exposure to chromium have been reported [71, 72, 73]. However, the low solubility of trivalent Cr in natural waters with pH between 6.5 and 8.5 could indicate a higher proportion of hexavalent Cr in these waters [74,75]. Based on Canadian guidelines for aquatic life protection which are 0.2-1.8 ug/L for Cd, 1-7 ug/L for Pb, 2-20 ug/L for Cr, and 2-4 ug/L for Cu [54], adverse effects linked to Cd, Pb, Cr, and Cu can be caused by these waters to living organisms. All the trace elements showed homogeneous variation in their concentration values, with CV varying between 7.90 for Cu and 42.66 for Cr. Positive asymmetries of trace element values were observed with Skewness values ranging from 0.11 for Cu to 0.88 for As (Table 2). Thus, the majority of the sites are in the zone of the lowest concentrations. Figure 2: Prediction maps of the spatial distribution of temperature (T\({}^{\circ}\)C), pH, conductivity (EC), TDS, salinity (Sa), and orthophosphate (PO\({}_{4}\)3\({}^{-}\)). Four different models were used for spatial patterns analysis of trace elements based on the kriging accuracy for each variable (Table 4). Indeed, the models chosen for spatial analysis were Gaussian (Cd), Stable (Pb, Ni, and As), Exponential (Cr, Cu, and Mn), and Spherical (Zn). These models were ideal for accurate data prediction because of their mean error (ME) very close to 0 and the smallest root mean square error (RMSE) obtained (Table 4) [29; 42]. Spatial variations in trace element concentrations were detected with nugget-sill ratios ranging between 0.27 and 81.90%. Indeed, high spatial dependence was recorded for Cr, Cu, and Mn (0.27-2%), whereas medium spatial dependence was observed for Cd (50.06%), Pb (46.94%), Ni (30.78%), and Zn (71.97%) [42; 68]. The range values vary from 0.02 km for As and Mn to 0.24 km for Pb. Similarities in spatial dependence of the concentration variabilities were observed between Cr, Cu, and Mn. The prediction maps (Figure 3) show a very distinct spatial distribution of trace element concentration. A similar spatial distribution was observed for Cd and Cr. Indeed, higher concentrations of these trace elements were found in the upstream (west) and downstream (east) regions of the hydrosystem. Similar spatial distribution was also observed for Pb, Cu, and Zn, with the highest concentration occupying downstream regions at the eastern part of the hydrosystem. Distinct zonal spatial variations were obtained for As and Mn. High concentrations were observed all over the hydrosystem, whereas low concentrations occupied a small area in the midstream part and the upstream in the northwestern part. The highest concentrations of Mn were obtained in the region of the upstream in the west.