PRELIMINARY PLANKTON INVESTIGATIONS IN THE GRAVEL PIT AND WINTERPONDS NEAR JAGODNO

Investigations of plankton populations have been performed in the gravel pit and two winterponds near the place Jagodno, Novo Čiće, in the vicinity of Velika Gorica. Our goal was to examine plankton composition of the gravel pit and winterponds, two ecosystems characterized by specific life–conditions which change with time and space. Investigations were conducted during June 2007. Plankton samples were collected from water surface layer at four locations (two locations in the gravel pit and one location in each of two winterponds). Along with plankton sample collecting, measurements were made of some physico–chemical parameters (water temperature, pH–values and dissolved oxygen content in water). Water temperature at two sampling locations in the gravel pit and one location at each of the winterponds depended on the surrounding air temperature, and ranged from 22.5ºC to 23.6ºC. pH–reaction was alkaline, ranging from 8. 23 to 9. 02. Dissolved oxygen content in the gravel pit was around 10 mg/O2; in winterponds it ranged from 7.6 to 9.7 mg/O2 (Table 1). At the gravel pit locations total number of 32 phytoplankton species were determined; in winterponds were determined 37 (microphytic species)? while zooplankton was represented in the phytoplankton community composition at the four locations with 5 species. Phytoplankton species determined in the samples from two gravel pit locations belonged to the system groups Dinophyta, Chrysophyta and Chlorophyta while in the samples from winterpond locations, along with the mentioned system groups, were found as well the representatives from the groups Cyanophyta/Cyanobacteria and Euglenophyta. Zooplankton species belonged to the groups Rotatoria, Cladocera and Copepoda (Table 2). In gravel pit locations dominated diatoms or Bacillarophyceae while in winterponds the majority of phytoplankton mass consisted of the representatives of the species Cyanophyta/Cyanobacteria and Euglenophyta. Qualitative analyses of plankton showed the presence of plankton species characteristic for ciprinid fishponds. At gravel pit locations, the saprobity value of P–B (saprobity — saprobicity)? index was 1.7 (characteristic for the first class water quality). At the locations 3 and 4 (winterpond locations) the P–B (saprobity — saprobicity)? index was 2.0 and 1.9, respectively (characteristic for the second class water quality). Based on the obtained results, the investigated locations are suitable for ciprinid fish culture.