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 <strong>of</strong> 145 kmfrom Naslavcea; site 5 – c. Dubasari, above the dam <strong>of</strong> the Dubsari water reservoir, 309 km from Naslavea; site 6 – 100m below the dam <strong>of</strong> the Dubasari water reservoir (310 km from the site 1). During the summer <strong>of</strong> 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 <strong>of</strong> major ions (Ca 2+ , Mg 2+ , Na + + K + , HCO 3-, SO 42-, Cl - ). The traditionalhydrochemical parameters <strong>of</strong> the river waters has served as additional indicators <strong>of</strong> potential impact <strong>of</strong> 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 <strong>of</strong> the components <strong>of</strong> the Dniester river waters determining the oxidation-reduction processeshas identified a series <strong>of</strong> regularities in seasonal and spatial dynamics. The hydrogen indicator (pH) for the duration <strong>of</strong>the year cycle was varying within the investigated segment <strong>of</strong> 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 <strong>of</strong>the initial site was lower than in other investigation sites. The seasonal variations were manifested by the decrease <strong>of</strong>this indicator almost in all the sectional lines <strong>of</strong> 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 <strong>of</strong> 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 <strong>of</strong> saturation <strong>of</strong> waterswith oxygen by 83% was observed also in summer at the Bosernita site. The investigation <strong>of</strong> saturation with oxygen atCosauti, Bosernita and Dubasari water reservoir has identified over saturation <strong>of</strong> 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 <strong>of</strong> reduction and oxidation processes was varying from the predominance<strong>of</strong> the reduction processes to neutral state and in average it can be characterized as close to neutral. In Mereseuca thewaters most <strong>of</strong>ten was predominant the reduction processes. The domination <strong>of</strong> reduction processes over oxidationprocesses was observed in summer period at Dubasari water reservoir as well.Table 1The content <strong>of</strong> redox components in Dniester waters between 12.08.05 and 24.08.06 (Numerator- the average value <strong>of</strong>the period, denominator - the limits <strong>of</strong> variation <strong>of</strong> 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
V. Gladchi et al./Chem.J.Mold. 2008, 3 (1), 70-76The ammonia ions in the section line <strong>of</strong> Dniester were present in concentrations 0.015 – 0,136 ml NH 4+/l.Starting from Cosauti towards the Dubasari hydroelectrical plant their content was steadily increasing. The maximalcontent was observed below the dam at Dubasari. The seasonal dynamics <strong>of</strong> ammonium nitrogen was manifested by the+increase <strong>of</strong> its concentration in autumn. In spring the NH 4ions were not identified in any site but Bosernita.-In average for the year, the content <strong>of</strong> NO 3in the section lines constituted 5.5 – 7.4 mg NO 3-/l, and the lowest-values were detected in autumn; the highest concentrations <strong>of</strong> NO 3were observed in spring in all the sites butNaslavcea.The nitrites, during the investigation period, were a permanent component <strong>of</strong> Dniester waters. Their absencewas registered only once in May 2006 above and below the Dubasari barrage. The average content <strong>of</strong> nitrites throughoutthe year constituted between 0.027 and 0.058 mg NO 2-/l. In summer the content <strong>of</strong> nitrites in Dniester waters wasincreasing, while in spring it was decreasing. The permanent presence <strong>of</strong> nitrites in the background <strong>of</strong> low content or-complete absence <strong>of</strong> ammonium nitrogen can occur due to unfavorable oxidation state and slow oxidation <strong>of</strong> NO 2toNO 3-.3-The phosphates were present in the river in quantities 0.11 – 3.22 mg PO 4/l. Their average concentrations in3-the sections lines varied in the range 0.48-0.73 mg 4/l. The maximal pollution with phosphates was observed in3-the summer <strong>of</strong> 2006 at Cosauti and Bosernita sites, and constituted respectively 3.22 and 1.37 mg 4/l. The seasonaldynamics have shown an increase <strong>of</strong> the phosphates content in the segment Naslavcea – Mereseuca in spring, anotherincrease being detected in summer between Cosauti and Dubasari.The average content <strong>of</strong> organic compounds according to the BOD 5in the section lines <strong>of</strong> the investigated sector<strong>of</strong> Dniester constituted 3.1 – 3.9 mg O 2/l. In summer this indicator was rising above the yearly average at Mereseucaand Cosauti sites and constituted respectively 4.6 and 3.7 mg O 2/l, in spring – at the Dubasari water reservoir (Bosernita– Dubasari, lower reach) and constituted respectively 6.1 – 5.0 mg O 2/l. At Naslavcea the maximal amount <strong>of</strong> organiccompounds was 4.45 mg O 2/l that was detected in spring.The hydrogen peroxide and the redox state <strong>of</strong> watersThe analyses <strong>of</strong> the waters <strong>of</strong> the sector under investigation have never detected an oxidant state throughout theperiod <strong>of</strong> research (table 2). The most favorable state, according to this parameter, was registered in September 2005when hydrogen peroxide was detected in the samples collected from all the sites (the range <strong>of</strong> concentrations: 1.44·10 -6 M– 9.52·10 -6 M) except Naslavchea. At that site the waters were continuously in reducing state, the hydrogen peroxidewas missing and only the organic substances <strong>of</strong> peroxidazic type that are easily titrated by hydrogen peroxide werepresent. The reducing state <strong>of</strong> water below the Naslavchea dam could be caused by a shift from the equilibrium statein the waters <strong>of</strong> the accumulation reservoir above the dam resulting from the inflow <strong>of</strong> substantial amounts <strong>of</strong> reducingperoxidazic substances. The negative impact <strong>of</strong> the resulted disequilibria has been attenuated along the investigationsegment <strong>of</strong> the river, that was confirmed by the presence <strong>of</strong> hydrogen peroxide in the waters <strong>of</strong> the Mereseuca site,where its concentration was the lowest (1.19 . 10 -6 M) in the hole investigated part <strong>of</strong> the river. The detection <strong>of</strong> hydrogenperoxide can be related to the occurrence in the segment Naslavcea – Mereseuca (18 km) <strong>of</strong> self-purification processesthat lead to the total oxidation <strong>of</strong> peroxidazic substances and to the low excess <strong>of</strong> hydrogen peroxide.The maximal content <strong>of</strong> H 2O 2in September 2005 was registered below and above the Dubasari dam (8.48· 10 -6 Mand 9.52·10 -6 M), that can be explained by the existence <strong>of</strong> large quantities <strong>of</strong> micr<strong>of</strong>lora that eliminates metabolic H 2O 2in the surrounding environment.Table 2The content <strong>of</strong> hydrogen peroxide and reducing substances (H 2O 2·10 -6 M/Red·10 -6 M) in the waters <strong>of</strong> Dniester River)Month, year Naslavcea Mereseuca Cosauti Bosernita Dubasari, above Dubasari, belowthe dam the dam09.2005 -1,191,771,449,528,481,10-----10.2005 1,241,051,90-1,52-------11.2005 0,320,350,70-0,330,42------03.2006 ----------0,900,9205.2006 0,30-0,50-0,500,40-0,30----06.2006 4,805,441,26------0,500,460,6408.2006 0,500,490,480,490,490,48------72
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