Taxonomical Composition and Functional Structure of Phytoplankton in Two Water Supply Reservoirs in Serbia - page 01

Material and Methods

The Bukulja reservoir (Figure 1) was formed in 1965 for water supply of the town of Arandjelovac when the upper part of the small river VelikaBukulja on Mountain Bukulja was dammed. The total capacity of this reservoir is 1.370.000 m3 (1.200.000 m3 being in use) and the surface of drainage area is 6 km2. It is 1500 m long, 300 m wide and 26 m deep. The dam is 120,5 m long and 24 m high. The Bukulja reservoir became insufficient for water supply with the increased growth of the town of Arandjelovac, so in 1976 the Garaši reservoir (Figure 1) was formed at the mouth of two small rivers: Velika Bukulja and Mala Bukulja. The total capacity of this reservoir is 6.270.000 m3 (5.270.000 m3 in use) and the surface of the drainage area is 15,9 km2. The dam is 380 m long and 29 m high (Karadžić et al., 2010). Water purifying plant is located on the reservoir Bukulja, on the peak elevation, ensuring the gravity water supply for consumers. Water pump Bukulja supplies the plant. During the refilling of the Bukulja reservoir from the Garaši reservoir through the water pump Garaši, one part of the discharge is directly sent to the water supply source plant. The refilling of the Garaši reservoir is done through the water pump located on the river Kačer. There are, therefore, three river flows and two reservoirs in the water supply system of Arandjelovac (Karadžić et al., 2010).

The samples for quality analysis from these two reservoirs were collected on water supply site by using the plankton net (pore diameter of 22 µm). The samples were samples were placed in 250 ml plastic bottles and fixed immediately with formaldehyde to a final concentration of 4%.

Algae were investigated directly from the samples by using ReichartDiastarTM microscope equipped with a PhotostarTM camera system, so some of the taxa were photographed. In the laboratory, for diatoms identification, the field samples were treated with concentrated acid (H2SO4) and KMnO4 to remove organic matter, and then washed several times with distilled water. After this process the material was airdried on coverglasses and mounted in Naphrax. Light microscope observations were made using a Zeiss AxioImager M.1 microscope with DIC optics and Axio Vision 4.8 software. Taxonomic identifications were made according to widely used taxonomic keys for all algae (Starmach, 1980, 1983; Huber-Pestalozzi et al., 1983; Krammer and Lange-Bertalot, 1986, 1988, 1991a, 1991b; Popovský and Pfiester, 1990; Komárek andAnagnostidis, 1998, 2005; Coesel and Meesters, 2007; Komárek, 2013).

Phytoplankton samples for quantitative analysis were collected by using a Ruttner's bottle (2 l volume) on different depths (Bukulja: 4m, 8m; Garaši: 0m, 4m, 8m, 13m). Samples were preserved at once with formaldehyde to a final concentration of 4% in 1 l plastic bottles. Quantitative analysis of phytoplankton were made by using Utermöhl method (Utermöhl, 1958) with an Olympus inverted microscope. Results were expressed as number of cells per ml. Phytoplankton biomass was calculated by geometric approximations, standard mathematics formula (Hillebrand, 1999; Sun and Liu, 2003) and expressed in μg/l. Average cell dimension values were obtained by measuring at least 25 units of existing taxon.

Only the taxa whose relative biomasses represented ≥ 5% in at least one sample were considered, and functional groups were determined for them. Determination of functional groups were made according to phytoplankton functional classification systems (Reynolds et al., 2002; Padiśak et al., 2009)


Figure 1: The map of the studied water supply reservoirs and sampling sites: Site 1- sampling site in the Garaši reservoir; Site 2- sampling site in the Bukulja reservoir.


Results and Discussion

Quality analysis of phytoplankton from both reservoirs shows that the total number of 194 taxa was present from 6 divisions: Bacillariophyta, Cyanobacteria, Chrysophyta, Chlorophyta, Dinophyta and Euglenophyta. From the total number of taxa, there are 160 present in Garaši reservoir, and 130 in Bukulja reservoir.

The highest species number (93 taxa) for both reservoirs together was recorded within Bacillariophyta and it constitutes 48% of all taxa. Other divisions presence for both reservoirs were as follows: Chlorophyta 28% (54 taxa), Cyanobacteria 13% (26 taxa), Euglenophyta 5% (10 taxa), Chrysophyta 4% (8 taxa) and Dinophyta 2% (3 taxa). The list of all phytoplankton taxa from both reservoirs is given in Table 1.

The highest number of taxa (81) in Garaši reservoir was recorded in October 2006 and the smallest number (55) was in September 2005. Regarding Bukulja reservoir, the highest number of taxa (63) was recorded in November 2005 and the smallest number (42) was also in September 2005. Percentage of algae divisions present in Garaši and Bukulja reservoirs and in total of these two reservoirs is given in Figure 2.


Figure 2. Percentage of algae divisions present in Garaši and Bukulja reservoirs and in total of these two reservoirs.