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196 Natura Montenegrina, 4/2005 INTRODUCTION The reservoir was formed by the Veternica River, 30 km upstream of the town of Leskovac at the place called Barje. The first, primary aim was to protect Leskovac from flooding waters, afterwards as the protection from sediments compiling, for regulation of flow and ensurance of guaranteed biological minimum. Today this reservoir is primarily used for water supply for town of Leskovac and the municipality of Lebane. Concerning the fact that the filling was ended in 1995, that year has been taken as a zero point for water quality determination. At maximum the reservoir has the volume of 40.6 · 10 6 m 3 , whilst the area is 139 hectares. In the conditions of normal USPOR the volume is 26.2 · 10 6 m 3 with maximal depth of 25 m. The average width is 300 m and the length, depending on filling, varies between 7.1 and 7.5 km. MATERIAL AND METHODS Republic Hydrometeorologic Service of Serbia has carried out the physico-chemical and biological examinations of water quality of Barje reservoir, since 1993, under the Programme of Systematic Surface Water Quality Examination. This Programme had established three localities of free water of reservoir, for sample taking: at the dam (A), at the central part of the reservoir (B) and at the entrance of the reservoir (C). On each locality, the samples are taken at three depths: 0.5 m under water surface (1), in the midde part of water coloumn (2) and by the bottom of the reservoir (3). Physico-chemical and biological examinations are carried out according to standard methodology for sampling and working. Material for biological analysis was collected by using plankton net, mesh size of 25 µm and hydrobiologic bottle after Ruttner, volume of 4.5 dm 3 . The samples have been fixed to by formaldehyde to the final concentration of 4 %. Transparency was measured by Secchi disc. The analysis of physico-chemical parameters was carried out by using standard analytical procedures by the methods of JUS-ISO, EPA. The phytoplankton qualitative analysis was carried out in biological lab of RHMS by using certain keys for determination, for each algal group separately. The determined taxa have been grouped in the divisions on the basis of classification system due to which algae are alligned in ten divisions (B l a ž e n č i ć , J. 1988.). Silicate algae have been determined from the material made by a standard procedure (P a t r i c k & R e i m e r , 1966.) with the formation of lasting preparations waxed in canada balsam. Trophic status of reservoir is given due to OECD reservoir (M a n d a v i l l e , S. M.2000.). RESULTS AND DISCUSSION The results of physico-chemical analysis are given in Tab. 1. Barje reservoir belongs to dimictic lakes of the medium-continental type that are characterized by two circulation periods, in Spring and Autumn, whilst there is the reversal thermal stratification. In the results of examinations from August 2003 there have been noted the temperature differences between layers of epilimnion and hypolimnion on the localities at the dam and in the central part of the lake, whilst at the entrance due to a small depth the water temperature is even from surface to the bottom. The examinations taken in September 2002 are pointing to the beginning of the Autumn circulation process. The water transparency in that year was
ĐURKOVIĆ, A. et al: Algologic Examinations and Trophic Status of Barje Reservoir relatively low that is characteristical for eutrophic lakes. In 2003 on the locality at the dam the measured transparency had values characteristical for mesotrophic lakes. The high pH values (from 7.38 to 8.50) have been noted that is caused by high bioproduction in water. The soluble oxygen values had the highest values in surface water layers. The lowest values of that parameter have been noted in 2003 at the entrance of the reservoir (8.55 mg/dm 3 ) and highest (9.6 mg/dm 3 ) at the dam. In surface water layers of the central part of the reservoir and of the dam (2002) also in a surface layer, the super saturation has been noted. The BOD values, are also the highest in surface water layers, due to the huge amount of biodecomposable organic materials. The COD that refers to contents of organic substances in water increases by depth. The primary nutrients concentrations are of a certain influence on a degree of a primary production of water ecosystems. The primary production is firstly regulated by the amount of available phosphorous (SEPA 1991). According to the categorization of primary nutrients belonged to fourth (IV) and the fifth (V) class. In 2003 the concentrations of Ntot matched the fifth (V) class, whilst the phosphorous concentrations in a vertical coloumn were in the second (II) and the third (III) class. Table 1. Results of physico-chemical water analysis of Barje reservoir god. A1 A2 A3 B1 B2 B3 C1 C2 C3 Parameter Depth (m) 2002. 2003. 0.5 0.5 15.0 14.5 30.0 29.0 0.5 0.5 7.0 12.0 15.0 25.0 0.5 0.5 1.0 1.5 1.5 3.5 Water temperature 2002. 22.0 17.2 15.0 22.0 20.0 16.8 22.2 22.2 21.8 ( 0 C) 2003. 24.0 11.4 8.3 24.6 19.0 10.0 24.2 24.0 24.0 Transparency (m) 2002. 2003. 2.6 3.5 2.5 2.5 1.0 1.9 pH value 2002. 2003. 8.3 8.55 8.1 7.9 7.9 7.6 8.3 7.38 8.0 7.9 8.0 7.8 8.3 8.40 8.2 8.30 8.2 8.08 Dissolved O2 2002. 9.6 3.1 1.8 9.5 4.7 3.5 8.7 8.4 8.6 (mg/dm 3 ) 2003. 8.81 5.26 4.57 8.90 7.02 3.72 8.55 8.32 8.38 % of water saturation by O2 (% O2) 2002. 2003. 110 99 32 48 18 39 110 108 52 76 38 33 100 103 97 99 98 101 BOD 2002. 1.2 1.2 1.2 8.3 1.5 1.6 1.5 2.1 1.0 (O2 mg/dm 3 ) 2003. 4.81 1.82 1.9 5.2 3.20 1.20 5.10 5.20 4.90 COD (O2 mg/dm 2002. 1.8 2.4 3.1 1.6 2.5 3.1 1.6 1.8 1.8 3 on KMnO4) 2003. 5.71 3.86 6.38 3.95 4.28 3.20 4.03 3.92 3.92 N tot 2002. 0.8 0.6 1.1 0.6 0.3 0.8 0.6 0.8 0.5 (N-mg/dm 3 ) 2003. 2.5 1.5 2.6 2.1 1.9 2.5 2.0 1.9 1.6 P tot 2002. 0.025 0.039 0.084 0.026 0.024 0.025 0.060 0.030 0.032 (P-mg/dm 3 ) 2003. 0.008 0.022 0.021 0.008 0.012 0.015 0.012 0.012 0.014 Silicium dioxide 2002. 17.0 19.0 17.0 17.0 19.0 15.0 13.0 15.0 14.0 (SiO2 mg/dm 3 ) 2003. 3.0 12.6 17.7 3.4 8.2 12.5 3.7 3.8 3.9 A relatively small variety has been noted by qualitative analysis, that does not show important changes compared to previous examinations (O b u š k o v i ć , L J . 1996; S i m i ć , S . 2000.). There have been determined 58 taxa from six algal divisions: Cyanophyta (5 taxa), 197
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