Yeniçağa Gölü'ndeki (Bolu) Zooplankton Biyokütlesinin Zamana Bağlı Değişimi

Abstract

In this study, the biomass changes of zooplankton in Yeniçağa Lake between May 2017- April 2018 and December 2021-November 2022 were examined depending on time, and parameters such as species richness and density of zooplankton were determined. In addition, some physicochemical properties of Yeniçağa Lake were examined in monthly field studies carried out between December 2021 and November 2022, and the relationship between zooplankton biomass and these parameters was interpreted using statistical analysis. The trophic level of Lake Yeniçağa was evaluated with chlorophyll-a, total phosphorus values and Carlson TSI Indexes, and according to the results obtained, it was understood that the lake was generally at the eutrophic level, but the trophic level approached hypertrophy in some months. It was determined that the zooplankton in Yeniçağa Lake consisted of a total of 17 species, 4 Cladocera, 4 Copepoda and 9 Rotifera species, in the period of 2017-2018, and a total of 19 species, 4 Cladocera, 3 Copepoda and 12 Rotifera species, in the 2021-2022 period. Copepoda made up 48%, Rotifera 38%, and Cladocera 14% of the zooplankton in the 2017-2018 period. In the 2021-2022 period, 83.08% of the zooplankton consisted of Rotifera, 12.84% of Copepoda and 4.09% of Cladocera group. A time-dependent change was determined in the numerical proportional contributions of the groups in the zooplankton. Accordingly, a very significant increase was observed in the organisms belonging to the Rotifera group in zooplankton. In the 2017-2018 period in Yeniçağa Lake, 70.42% of the zooplankton biomass was composed of Copepoda, 27.99% Cladocera and 1.60% Rotifera. In the 2021-2022 period, 50.59% of the zooplankton biomass was composed of Copepoda, 32.03% of Cladocera and 17.38% of Rotifera. Time-dependent changes were determined in the proportional values of the groups contributing to the zooplankton biomass. Accordingly, while the proportional contribution to the total biomass of the zooplanton increased in Rotifera and Cladocera groups, the proportional contribution decreased in the Copepoda group. Pearson Correlation analysis was performed to determine the relationship between zooplankton biomass and some physicochemical parameters of water. Analysis results showed that zooplankton biomass was negatively affected by pH, turbidity and chlorophyll-a, and positively affected by electrical conductivity, TDS and light transmittance. It was determined that the average total biomass value in the zooplankton was calculated as 25,691 µg/m3 in the period of May 2017-April 2018 in Yeniçağa Lake, and the average total biomass value was calculated as 47,884 µg/m3 in the period of December 2021- November 2022, showing a significant increase depending on time. In addition, the temporal difference was statistically significant (p < 0.05). As a result, when the two time series are considered in this study, a decrease in the organisms in the Cladocera and Copepoda groups and an increase in the organisms in the Rotifera group were determined in terms of density and biomass. In addition, while the Rotifera group made a significant contribution to the zooplankton numerically, the contribution of this group to the biomass remained at a lower level than the other groups.