Seasonal variation of the benthic diatoms in Büyükçekmece Dam Lake

This study aims to detect benthic diatoms in Büyükçekmece Dam Lake and the effective ecologic variables on their distribution. To this end, the study was conducted seasonally in 2019, and samples collected from 5 different stations were examined. Accordingly, a total of 103 benthic diatom species, being 6 centric and 97 pennates. 54 of the species were found to be new records for the lake. No significant differences were found between seasons and stations in terms of species diversity. Achnanthidium sp. and Cocconeis placentula species were found to be more dominant throughout the study, while Gomphonella olivacea was more dominant particularly in February sampling. Pennate diatom species were observed more frequently than centric diatom types, and both groups of the species preferred epipelic habitat (87 taxa) more than epiphytic habitat (66 taxa). Among the ecological variables examined within the scope of the present study, temperature (5.01-26.65 °C), salinity (0.25-0.88), dissolved oxygen (3.87-18.96 mg / L), pH (7.49-8 , 28), conductivity (0.312-1.322 mS / cm), total dissolved solid (0.271-1.125 g / L), suspended solid material (0-0.024 g / L), chlorophyll-a (0.08-3.20 µg / L), biological oxygen need (3.79-20.46 mg / L), nitrite+nitrate-N (0.77-98, 38 µg-at N / L), ammonium-N (0.04-4.34 µg-at N / L), phosphate-P (0.69-41.74 µg-at P / L), silicate-Si (2.32-122.17 (µg-at Si / L), total nitrogen (0.81-99.56 µg-at N / L) and total phosphorus (1.24-108.39 µg-at P / L) values were measured. The Spearman's rank correlation was conducted to determine the relationship between benthic diatom species and ecological variables. Accordingly, it was found that salinity, conductivity, SSM, TDS, and nutrients are more effective on the species, and the nutrients have an effect on species, particularly those living in epilithic habitats. In addition, Shannon-Weaver's diversity, Simpson's dominance, Pielou's regularity indexes, together with frequency and similarity analyzes were also applied. The Bray-Curtis index was used to determine the similarity between stations and habitats in terms of species abundance. Besides, the Euclidean distance was calculated to reveal the similarity between stations and between sampling periods in terms of ecological variables, and it was detected that the stations and sampling periods were grouped among themselves throughout the study. The water quality classes, ecological status, and trophic level of the stations in the dam lake were also detected. It was found that most stations have a second-class water quality (good, oligo-mesotrophic), and no eutrophic and hypereutrophic conditions were observed.