Acta Facultatis Ecologiae - Technická univerzita vo Zvolene

116mg.dm -310,009,008,007,006,005,004,003,002,001,000,001 2 3 4 5 6 7 8 9 10 11 12MonthsO2Fig. 1 Concentrations of dissolved oxygen in mg.l –1 in dependence on sampling time°C25,020,015,010,05,00,01 2 3 4 5 6 7 8 9 10 11 12Months10,009,008,007,006,005,004,003,002,001,000,00m g.dm -3Temperature of waterDissolved oxygenFig. 2 Relation between the average temperature of water and dissolved oxygen concentrationAs for the sampling place the highest averageconcentrations of dissolved oxygen were measuredin sampling sites No. 1 (6.0 mg O 2.l –1 ) and No.4 (5.5 mg O 2.l –1 ). Sampling site No. 1 is situatedon the inflow of the river Žitava into the NatureReserve and sampling site No. 4 is situated on thenarrowest place of the NR where water flow hasthe highest speed. These sites are characterized bypermanent water flow. Lower values of dissolvedoxygen were in sampling sites No. 2, 3, 5 and 6(Fig. 3) because these sites are typical wetlandecosystems. They are overgrown by aquatic plantsand there is a huge amount of organic matter fromextinct plants in sediments thus good conditionsfor accumulation of organic substances in waterare created. Different conditions in sampling sitesNo. 2, 3, 5 and 6 were probably the reason of lowerconcentrations of dissolved oxygen compared withsampling sites No. 1 and 4 Beňačková, Noskovič(2005) and Sedláková (2004) measured low concentrationof dissolved oxygen in similar localities(the NR Žitavský luh and the NNR Parížske močiarerespectively).Based on calculated characteristic values ofdissolved oxygen and according to the standard weranked all sampling sites into the 5 th class of the watersurface quality (very strongly polluted water).Total content of organic substances in water inthe NR Alúvium Žitavy was evaluated according toCOD Crvalues. In dependence on sampling time thehighest values were determined in summer monthswith the maximum in August (129.3 mg O 2.l –1 ).Beňačková, Noskovič (2005) measured the highestvalues of COD Crin August in the NR Žitavskýluh, too. High values of COD Crin summer monthsare obviously related to intensive decomposition oforganic matter. The lowest values were measuredin winter season with the minimum in December(52.7 mg O 2.l –1 ) (Fig. 4). The fall of COD Crvaluesin winter can be connected with unsuitable thermal