# Spatial Variation of Water Chemistry in Aries River Catchment, Western Romania
## 3 Results
### Cations and Anions Characteristics
Cluster 4 grouped samples A1, A2, A3, A4, A5, A6 and A10, based on the low concentrations of F\({}^{-}\), Cl\({}^{-}\), NO3\({}^{-}\), SO4\({}^{2-}\), Mg and K. A13 and A8 were not linked to a particular cluster, due to a main characteristic of the sample (in the case of A8, due to a high concentration of SO4\({}^{2-}\) and, in the case of A13, high concentration of HCO3\({}^{-}\)). The correlations and similarities among the chemical indicators were established with the agglomerative hierarchical cluster analysis. The performed HCA classifies all 30 water samples (A1-A30) into four clusters (Figure 5). Cluster 1 (C1) included pH, NO3\({}^{-}\), Al, Cd, Ni and Cu, Cluster 2 (C2) contained almost all of the anions (Cl\({}^{-}\), F\({}^{-}\), HCO3\({}^{-}\), SO4\({}^{2-}\)), Ca, TDS and EC, while Cluster 3 (C3) included the rest of the cations (Mg, K, Na) and most of the metals (Sr, Cr, Ba, Fe, Pb, Co, Zn and Mn). TDS, SO4\({}^{2-}\) and Ca were grouped, suggesting the same source. The high values of TDS were due to the natural dissolution of gypsum or due to anthropogenic activities. NO3\({}^{-}\), Al, Cd, Ni and Cu (C1), and, respectively, Cr, Ba, Fe, Pb, Co, Zn and Mn (C3) were distant from EC/SO4\({}^{2-}\), indicating that those parameters behave quite differently. Therefore, a possible mechanism of establishing the main processes controlling the chemistry of surface waters was established. Mining activities are a source of toxic metals, while natural processes, such as the weathering of gypsum, could be the main source of Ca and SO4\({}^{2-}\)[55]. NO3\({}^{-}\), Mn and As were clustered in sample A12, indicating the same source and similar chemical behavior. The water types of the analyzed samples were determined using the Piper and Durov diagrams (Figure 6a,b). The hydrochemical facies and different types of waters were assessed based on the major cations and anions projected into the diamond field situated in the center of the Piper plot [32, 42]. In the cation plot, most of the studied water samples were situated in the left corner, where the Ca concentration was high, indicating its dominance. In contrast, the anion diagram showed that most of the water samples were distributed in the lower-left corner, characterized by the dominance of HCO3\({}^{-}\) over Cl\({}^{-}\) and SO4\({}^{2-}\). However, two samples were situated in the upper corner and dominated by SO4\({}^{2-}\) over Cl\({}^{-}\) and HCO3\({}^{-}\). Figure 4: The logarithmic distribution of chemical parameters concentrations (HCO3\({}^{-}\), Cl\({}^{-}\), NO3\({}^{-}\), K, Na, Mg, SO4\({}^{2-}\), Ca) among the sampling points with the corresponding dendrograms. The overall characteristics of the chemistry in the surface water samples, according to the Piper diagram, are the dominance of the alkaline earth elements (Ca and Mg) over the alkaline elements (Na and K) and for the weak acids (HCO3\({}^{-}\)) over the strong acids (SO4\({}^{2-}\) + Cl\({}^{-}\)). The Piper and Durov diagrams showed that the water samples were divided into two main types: Mg-HCO3\({}^{-}\) type (A1-A6, A8, A12, A14, A16-A30), indicating their carbonate-dominant lithology and Ca-Cl\({}^{-}\) type (A7, A9, A10, A11, A13, A15). The Durov plot also indicated that the majority of samples are alkaline, except for A7, A9 and A13, which were characterized by low pH values. Figure 5: Hierarchical cluster analysis of the physico-chemical indicators for the studied samples. Figure 6: Durov (**a**) and Piper (**b**) diagrams describing the water facies of the studied surfacewaters.