Seasonal Variation of Epipelic Diatom Assemblages and Their Relationships with Abiotic Variables in the Utility and Drinking Water Source of İstanbul: Büyükçekmece Reservoir

In this study, the distribution and composition of epipelic diatoms in Büyükçekmece Reservoir, which is one of the most important and main freshwater resources for İstanbul, Türkiye were investigated seasonally. Epipelic diatom samples were collected from five different stations each season (February, May, August, and November) in 2019. A total number of eighty-seven taxa belonging to thirty-seven genera were identified, six of which were centric and eighty-one were pennate; five of the epipelic species were new record diatoms for the Büyükçekmece Reservoir. The highest number of epipelic diatom species were encountered in February while the lowest was in November. Considering the frustule counts, it was observed that the species that increased their relative abundance changed in each sampling period. Consequently, it was observed that Gomphonella olivacea was the most abundant in February, Navicula reichardtiana in May, Achnanthidium sp. in August, and Cocconeis placentula in November. Shannon-Weaver Diversity Index showed that the highest diversity of diatom species was determined in February (station 4), and the lowest was observed in August (station 3). According to the results of redundancy analysis, it was observed that silicate-Si, conductivity, and temperature were the most efficient variables in the distribution of the epipelic diatom species.