chemistry journal of moldova

V. Gladchi et al./Chem.J.Mold. 2008, 3 (1), 70-76Naslavcea, below the Dniestrovsk dam, 200 m from the buffer reservoir; site 2 – v. Mereseuca, 18 km from the dam,site 3 – v. Cosauti, 87 km from the dam and buffer reservoir; site 4 – v. Bosernita located at the distance of 145 kmfrom Naslavcea; site 5 – c. Dubasari, above the dam of the Dubsari water reservoir, 309 km from Naslavea; site 6 – 100m below the dam of the Dubasari water reservoir (310 km from the site 1). During the summer of the year 2006 twomore sites have been added between the first and second sites. One was located at the fourth km from Naslavcea andthe other one was located at v.Verejeni, 6 km from Naslavcea. The sites located between Naslavcea and Cosauti werecharacteristic for the river-bed flow while the sites 4-6 were located very close to the Dubasari water reservoir.The water samples were collected from the upper horizons (0,5 – 0,6 m). The measured hydrochemical indicatorsincluded hardness, mineralization and the content of major ions (Ca 2+ , Mg 2+ , Na + + K + , HCO 3-, SO 42-, Cl - ). The traditionalhydrochemical parameters of the river waters has served as additional indicators of potential impact of the waterreservoir on the river waters flowing from the barrage. Redox components measured included: the temperature, thedissolved oxygen, pH, Eh, rH 2, BOD, COD, NH 4+, NO 3-, NO 2-, PO 43-, Cu(II), Fe(III), 2 2, and radicals.ResultsRedox active componentsThe assessment of the components of the Dniester river waters determining the oxidation-reduction processeshas identified a series of regularities in seasonal and spatial dynamics. The hydrogen indicator (pH) for the duration ofthe year cycle was varying within the investigated segment of the river from 7.3 till 9.1, its average values constitutedrespectively 7.8 at Naslavcea and 8.2 at Dubasari water reservoir (at the barrage). Practically at all the times the pH ofthe initial site was lower than in other investigation sites. The seasonal variations were manifested by the decrease ofthis indicator almost in all the sectional lines of the water flow.The dissolved oxygen was present in the Dniester waters during the investigation continuously, however, in thewater masses, coming into Naslavchea pool from Novodnestrovsc’s water reservoir; its content was reaching normalsaturation only in spring. In summer the saturation of water with oxygen constituted 70.5% and was decreasing incertain periods down to 52%; in autumn the average saturation was equal to 79.5%. The decrease of saturation of waterswith oxygen by 83% was observed also in summer at the Bosernita site. The investigation of saturation with oxygen atCosauti, Bosernita and Dubasari water reservoir has identified over saturation of Novodnestrovsc water with oxygenup to 158 – 177%.Novodnestrovsc’s waters have demonstrated during the investigation an instable oxidation – reduction state.According to the rH 2, at Naslavcea the ratio of reduction and oxidation processes was varying from the predominanceof the reduction processes to neutral state and in average it can be characterized as close to neutral. In Mereseuca thewaters most often was predominant the reduction processes. The domination of reduction processes over oxidationprocesses was observed in summer period at Dubasari water reservoir as well.Table 1The content of redox components in Dniester waters between 12.08.05 and 24.08.06 (Numerator- the average value ofthe period, denominator - the limits of variation of the indicators)SiteParameter7.8pH7.3-8.5rH 227.7rH 226.9-28.68.7mg/l 4.8-12.0[O 2] % 80.652-101[NO 3-], mg/l 5.841.9-8.4[NO 2-], mg/l 0.0270.008-0.054[NH 4+], mg/l 0.0210.0-0.073-[PO 4], mg/l 0.480.21-0.77CBO, mgO 2/l 3.31.2-4.45[H 2O 2]·10 6 MNaslavcea Mereseuca Cosauti Bosernita Dubasari, abovethe barrage1.020.0-4.88.117.7-8.527.225.5-28.011.658.2-14.7109.987.2-127.07.423.9-10.70.0370.014-0.0780.0150.0-0.100.540.16-0.923.130.6-5.61.220.0-5.448.248.0-8.628.027.6-28.412.58.9-17.0118.897-1875.681.7-10.70.0270.006-0.0520.0440.0-0.200.730.11-3.223.211.0-5.830.950.0-1.98.07.3-8.428.427.2-30.511.37.5-14.6107.283-1586.61.6-14.20.0270.012-0.0420.060.0-0.200.520.21-1.373.61.5-6.10.320.0-1.448.27.4-9.027.525.3-29.011.17.8-14.7113.388-1715.50.9-12.00.0580.0-0.2310.0710.0-0.320.460.12-0.673.91.4-6.71.760.0-9.52Dubasari, belowthe barrage8.157.6-9.127.122.1-29.210.68.1-15.2107.695-1336.940.6-13.40.030.0-0.0950.1360.0-0.540.520.22-0.823.71.9-5.01.40.0-8.4871