Diversity of benthic diatoms in relation to environmental factors in two Bulgarian reservoirs

Littoral diatom communities in two reservoirs in Bulgaria - Koprinka and Zhrebchevo - were studied to determine the qualitative and quantitative composition in relation to major environmental factors. The total number of diatom taxa recorded in the epilithon was 173. Canonical correspondence analysis was used to explore the relationships between environmental variables and patterns in the epilithic diatom assemblages. Transparency, temperature, pH and dissolved oxygen were found to be the most important environmental factors which determined the distribution of diatoms in summer and autumn in the Zhrebchevo Reservoir. Conductivity and concentrations of calcium and bicarbonate ions were the most important environmental factors for the distribution of diatom communities in the Koprinka Reservoir. The Zhrebchevo Reservoir, which is infested by Dreissena polymorpha, was characterized by much higher rates of benthic primary productivity than the uninfested Koprinka Reservoir.