Phytoplankton and Trophic Status of Bovan Reservoir

1. Phytoplankton, Physico-chemical characteristics, Trophic status and Saprobiological characteristics of Bovan reservoir SNEŽANA ČAĐO, ALEKSANDAR MILETIĆ & ALEKSANDRA ĐURKOVIĆ Republic Hydrometeorologic Service of Serbia, Belgrade, Serbia and Montenegro

2. The Bovan reservoir is situated in south-east of Serbia, near the town of Aleksinac It is made on the River Moravica, the right tributary of River Južna Morava, in 1978. At the beginning of forming and building, the errors have been made: The reservoir is not properly located, nor the field for it has been properly prepared The waters of River Moravica and River Jošanicka bring the sewage of Sokobanja town, ''Soko'' mine, and the effluents of surrounding dwellings into Bovan reservoir Non-adequate preparation of field for the building of reservoir, insufficient protection of catchment area and huge income of nutrients, particularly in summer period during the touristic season, ended in euthrophication of Bovan reservoir. One of the most obvious consequences of euthrophication is water "blossoming'' as the result of destruction of self-regulation process in ecosystem Introduction

3. The Bovan Reservoir

4. The results of physico-chemical analysis of Bovan reservoir in July 2003.

5. 98 taxa have been determined from seven divisions of algae: Cyanophyta9 taxa Chrysophyta 2 taxa Bacillariophyta30taxa Xanthophyta 2 taxa Pyrrhophyta 3 taxa Euglenophyta 4 taxa Chlorophyta48 taxa Dominant species Aphanizomenon flos-aquae (L.) Ralfs from the group of Cyanophyta Subdominant species Ceratium hirundinella (O.F.M.) Bergh from the group ofPyrrophyta The results of qualitative phytoplankton analysis

6. The ratio between the concentrations of total phosphorous and sillicium-dioxide in Bovan reservoir • The increase in ratio of Ptot against the soluble sillica in reservoir water, which can be caused by antrophogenic influence, will end in the change of phytoplankton community contents. The domination of sillicate algae will be replaced by the domination of bluegreen algae or flaghelates • The examination results point out on high ratiobetween Ptot against soluble sillica which has beside the domination of bluegreen algae, also conditioned the presence of smaller centric forms among sillicate algae.

7. The results on density and biomass of phytoplankton and concentration of chlorophyll-a of Bovan reservoir in July 2003.

8. The density and biomass of phytoplankton and chlorophyll-a ratio of Bovan reservoir in July 2003. • Comparing the values of phytoplankton density, its biomass as well as the degree of primary production, given by the concentration of chlorophyll-a it can be concluded that their highest values are noted in surface water at the entrance of reservoir, and the lowest values at the dam locality at the highest depth. • It can be also concluded that the variations of density and biomass values follow the variations of concentration of chlorophyll-a values

9. The percential presence of certain algal groups and species in phytoplankton in comparison to the density and biomass

10. The values of Saprobic indices on sampling locality of Bovan reservoir in July 2003 • The results of saprobiological analysis show that in reservoir water the dominant organisms were those of β-mesosaprobic and oligosaprobiczone. The values of saprobic indices varied from 1.63, in the deepest water at the dam locality and in the central part of the reservoir, respectively, up to 1.79 in the middle water at the entrance of reservoir

11. Classification of the trophic status of Bovan reservoir • In the period of examination according to OECD classification of trophic status of the lakes and reservoirs, Bovan reservoir can be defined as euthrophic. • At the entrance of the reservoir the average values of concentrations of total phosphorous, chlorophyll-a and transparency are characteristic for hypereuthrophic lakes.

12. In surface water, the water “blossoming” was noted, which is the consequence of euthrophication high development of bluegreen algae is the consequence of: the high water temperature lower water level suitable meteorological conditions very high nutrients concentrations morphometry of the reservoirs. The increased organic production ended in simplification of ecosystem and the disturbance in its function. The species diversity has been decreased and water quality is worsened. By the decomposition of algal biomass the decaying processes are increased with the increased consumption of oxygen up to its deficit in the lower water. The organic compounds are accummulated in water as the result of algal decomposition. Phitodethritus precipitates on the bottom of reservoir. From the sediment compilations, which are rich in organic and mineral compounds, in the conditions of oxygen deficit, in the period of thermic stratification, the resources of nutrients are recharged, first of all orthophosphates. Failuresmade during the forming of reservoir, morphometric characteristics, washing off the agricultural fields from the very neighbourhood of the reservoir and the high income of nutrients and other pollutants by River Moravica ended in increased euthrophication and ecosystem degradation. Conclusion