# Spatial Variation of Water Chemistry in Aries River Catchment, Western Romania
## 2 Methodology
### Sampling and Analytical Procedures  
The study area was selected based on the impacts generated by the mining and industrial activities on the water resources (Figure 2). To evaluate the quality of the surface water, a field survey was conducted across the Aries River catchment. A number of 30 samples were collected from the mainstream (17 samples--A6, A12, A15-A30) and from the tributaries (13 samples--A1-A5, A7-A11, A13, A14) in November 2018.  
The samples were collected with a \"Grab\" device submerged at 20 cm under the water in polyethylene bottles pre-washed with 0.1N HNO3.The water samples were kept at 4 \({}^{\circ}\)C until the physico-chemical analysis, but no longer than 24 h.  
The pH and electrical conductivity (EC) were measured on-field by using a portable 350I multiparameter (WTW, Weilheim, Germany). The total dissolved solids (TDS) were determined by gravimetry, while bicarbonates (HCO3\({}^{-}\)) were determined by titration with 0.1 N HCl in the presence of bromocrossed green indicator. The anions (F\({}^{-}\), Cl\({}^{-}\), NO2\({}^{-}\), NO3\({}^{-}\), PO4\({}^{3-}\), SO4\({}^{2-}\)) concentration was measured by ion chromatography using an IC 761 Compact equipment (Metrohm, Herisau, Switzerland) after filtering the samples with 0.45 \(\upmu\)m cellulose acetate membrane filters(Isolab, Eschau, Germany), used with no further purification treatments. Samples were directed injected into the equipment, characterized by a flow of 0.7 mL/min, 7.5 mPa pressure and 15.0 \(\upmu\)S/cm electrical conductivity. Anions were separated through the anions exchange column and detected with the help of a conductivity detector [29].  
For the determination of metals, the samples were filtered with 0.45 \(\upmu\)m cellulose acetate membrane and acidified with 65% HNO3. The major cations (Fe, Na, Mg, K and Ca) were analyzed through an inductively coupled plasma optical emission spectrometer(ICP-OES, Perkin Elmer, Waltham, MA, USA), while the trace metals (Ni, Cr, Co, Cu, Zn, Cd, Pb, Mn, Ba, Al, Sr and As) were analyzed through an inductively coupled mass spectrometer (ELAN DRC II ICP-MS, Perkin Elmer, Waltham, MA, USA), due to the very low sensitivity of the equipment [29]. The instruments calibration was performed using  
Figure 2: Location of the sampling points and the main tailings impoundments in the Aries River catchment.  
analytical curves prepared with a multi-element standard solution from ICP Multi-Element Standard Solution IV (CertiPUR Merck, Darmstadt, Germany) in case of the ICP-OES and PerkinElmer Instrument Calibration Standard 3 in case of the ICP-MS.  
In order to ensure the quality of the results, calibration standards, duplicate samples and procedural lab blanks were prepared and determined, in concordance with [PERSON] et al. [30]. The accuracy of the metal determinations was tested using the 1643f NIST certified reference material (National Institute of Standards and Technology, Gaithersburg, MD, USA), while the anions were determined according to the IC1 Multi-element standard (CertiPUR Merck, Darmstadt, Germany). The mean recoveries ranged between 94% and 105% for the metals and between 89% and 102% for the anions.  
All reagents were of analytical grade and were used without any further purification. Ultrapure water from a Millipore system (Molsheim, France) was used for all dilutions.