Relationship of Epilithic Diatom Communities to Environmental Variables in Yedikır Dam Lake (Amasya, Turkey)

In order to evaluate the composition and seasonal variations of the epilithic diatoms in Yedikır Dam Lake were studied using samples collected from the stones in the barrier area between November 2004 and April 2006. The diatom communities were diverse; 88 taxa were found, belonging to the Bacillariophyta. Cymbella minuta, Cyclotella ocellata and Encyonema silesiacum have become the most abundant organisms in the epilithon. Environmental variables together with biological data obtained during the monthly routine biomonitoring of epilithic samples in the dam were analysed to understand variability of epilithic diatom communities and their relationships with environmental variables. Moreover, cluster analysis was applied to the epilithic algal communities and the seasonal variations of the samples were classified according to their similarity levels. Speciess richness and shannon diversity of the samples which were counted were measured in monthly periods. The results of the diversity analysis and the counting did not exactly match up with each other. Multivariate analyses indicated that both the regional distribution and seasonal variation of some epilithic diatoms (e.g. Cymbella spp., Nitzschia spp., Amphora delicatissima) are mainly driven by nutrient concentrations. Furthermore, epilithic diatoms are predominantly affected by geochemical characteristics including pH and total alkalinity (CaCO3) levels.