# Spatial Variation of Water Chemistry in Aries River Catchment, Western Romania
## 3 Results
### Cations and Anions Characteristics  
The river chemistry is generally associated with human and atmospheric inputs: rock and soil weathering, evaporation and crystallization [42; 52]. Ca (56.0 \(\pm\) 52.1 mg/L) was the dominant major cation across the Aries River catchment, followed by Na (7.77 \(\pm\) 1.98 mg/L), Mg (6.99 \(\pm\) 4.52 mg/L) and K (2.96 \(\pm\) 1.96 mg/L). Na concentration ranged between 1.90 and 14.6 mg/L, with the maximum concentration measured in A27 (Table 4). The highest levels of Mg, K and Ca were identified in A7 and A9. The Ca and Mg concentrations in the water samples from the Aries River catchment were higher than 75% of the total cation amount from the studied area, reflecting the predominance of carbonate weathering in the surface water. By contrast, HCO3\({}^{-}\) (118 \(\pm\) 59.7 mg/L) and SO4\({}^{2-}\) (80.5 \(\pm\) 94.8 mg/L) were the most abundant major anions in the surface waters. The main sources of bicarbonate are the weathering and dissolution processes of different rocks, such as calcite, carbonate, silicate and dolomite. The increasing trend of SO4\({}^{2-}\) concentration in A7 was not attributed to natural fluctuations but related to the industrial and agricultural activities in the Aries River catchment. The samples with the lowest SO4\({}^{2-}\)concentration are also associated with the lowest TDS values. The NO3\({}^{-}\) concentrations ranged between 0.5 and 2.5 mg/L. Generally, the lowest values of NO3\({}^{-}\) are correlated to the highest TDS values, except for sample A13, which was the richest sample in NO3\({}^{-}\) and had a high value for the TDS. Regarding the Cl\({}^{-}\) concentration, high values were noticed in samples A7 (42.9 mg/L) and A13 (45.8 mg/L), while in the rest of the samples, Cl\({}^{-}\) ranged between 1.19 and 20.8 mg/L. Furthermore, the chloride (Cl\({}^{-}\)) concentration indicated a low atmospheric contribution in the river catchment area. The highest F\({}^{-}\) concentration was determined in sample A13 (0.33 mg/L), while the lowest was in samples A1, A2, A4 and A6. NO2\({}^{-}\) and PO4\({}^{3-}\) were lower than the quantification limits (0.05 mg/L) of the method. The low concentrations of anions in the samples A1-A6, A17-A24 were due to the lithology, low human interference and slow weathering rate. The high standard deviations of the anions indicated that the data were usually spread due to the spatial variations among all sites and possible anthropogenic impacts. Other surface waters from Europe are characterized by comparable concentrations of anions, ranging between 0.01 and 0.19 mg/L NO2\({}^{-}\); 4.51 and 6.49 mg/L NO3\({}^{-}\); 0.66 and 3.33 mg/L PO4\({}^{3-}\); 23.5 and 265 mg/L SO4\({}^{2-}\)in Coruh River Basin (Georgia and Turkey) and 30.0 and 2000 mg/L Cl\({}^{-}\), 0.1 and 30.0 mg/L NO3\({}^{-}\) and 550 and 1000 mg/L SO4\({}^{2-}\)in El Avenue River (Spain) [53; 54]. The high values of EC and TDS and the high concentrations of HCO3\({}^{-}\), SO4\({}^{2-}\), Mg, K, Ca and Pb determined in samples A7, A9 and A13 clearly indicated an input of mine drainage from the mining-affected sites. Ca and HCO3\({}^{-}\), K and NO3\({}^{-}\), Mg and SO4\({}^{2-}\) were observed to have similar spatial variations (Figure 4). The trend of the highest composition of Ca and HCO3\({}^{-}\) in the Aries River was likely primarily derived from the dissolution of dolomite and from the dissolution of calcite (the upper and middle catchment area is represented mostly by karst landscape), while, based on the cation and anion concentrations, four different clusters were obtained. According to the hierarchical cluster analysis (HCA), four clusters were grouped, as indicated in Figure 4. Cluster 1 was formed by samples A7, A10 and A11, due to high values of Ca and SO4\({}^{2-}\).