Çubuk gölünün (Bolu, Türkiye) iklimsel ve hidrolojik değişimlerinin Ostrakoda (Crustacea) türleri ve limnoekolojik yapı üzerine etkilerinin belirlenmesi

During this study, samples were collected from 11 stations (5 being littoral and the other 6 vertical) in Lake Çubuk (Göynük, Bolu, Turkey) between July 2008 and November 2010. 17 species belonging to 10 genera (Candona neglecta, C. candida, C. sanociensis, C. weltneri, Pseudocandona albicans, P. eremita, P. semicognita, P. sucki, Fabaeformiscandona brevicornis, F. japonica, Physocypria kraepelini, Cypria ophtalmica, Ilyocypris gibba, Cypridopsis vidua, Limnocythere inopinata, Trajancypris serrata, Prionocypris zenkeri) were detected. One of them (F. japonica) was registered as a new report for the Turkish Ostracoda fauna, yet another (P. sucki) was registered for the second time. Unweighted Pair Group Mean Averages (UPGMA) of 10 species displayed clustering relationships based on ecological preferences among three groups. According to Spearman Correlation Analysis concerning 13 species and nine environmental variables, C. sanociensis showed positive relation with pH and Biological Oxygen Demand (BOD5), while C. weltneri was the only species showing negative correlation with dissolved oxygen. Canonical correspondence analysis (CCA) explained 77% (±1.74% error) of the relationship between the species and four environmental variables (temperature, electrical conductivity, turbidity and redox potantial). The overall surface area and the total volume of the lake was estimated at 16.03 hectares and 651.300 m3 on the bathymetric map. The length of the lake was 685 m, when its width was measured about 430 m during the present study. The depth of the lake reached to maximum level in spring (8.5 m) and its Secchi disc transparency was about 134.3 cm. According to sedimentation analyses, the lake accumulated 0.84 cm of sediment on average per month, while no remarkable accumulation was detected in pesticide (OCP) analyses. According to Piper diagram analyses water chemistry of the lake evolved from Ca-Mg-HCO3 water type to Na-Ca-HCO3 dominance. This result was confirmed by Principal Component Analysis (PCA). According to thermal stratification data, isogram (isopleth) results, stability analyses, stratification index (SI) and Wedderburn (W) values, Lake Çubuk appeared to be dimictic. Moreover, according to Wedderburn formulation, wind was the more efficient factor than temperature during the turnover time. Based on the average results of both Carlson Trophic State Index (CTSI) and Burns Trophic Level Index (BTLI), the lake has reached the mesotrophic level at the end of this study. It has been found out that especially the Fall Turnover, ion content and eutrophication rate were very important factors on species composition. Results indicated that swimming and cosmopolitan species were more widespread. Keywords: Ostracoda, dimictic, mesotrophic, Piper Diagram, Lake Çubuk, Bolu