Benthic diatom flora in relation to chemical and physical factors in high mountain lakes in the Rila Mountains (southwestern Bulgaria)
Ognjanova-Rumenova, Nadja; Botev, Ivan; Kernan, Martin
A survey of nine lakes in the Rila Mountains, SW Bulgaria was carried out as part of a broader pan-European study of mountain lakes. The aim of this paper is to study the relationships between the benthic diatom flora and the physical and chemical features of the lakes. A total of 166 diatom taxa belonging to 32 genera were observed in the epilithon samples from the study lakes. The Shannon-Weaver Index for the nine lakes varied between 2.70 and 4.50. The composition of the benthic diatom communities in the studied lakes showed relationships between species diversity and the main chemical gradient (pH, alkalinity and conductivity). The major patterns in diatom distribution within each lake were determined by Detrended Correspondence analysis (DCA). Two main groups of lakes were distinguished. The first group included mostly deep, more alkaline lakes, where the circumneutral and alkaliphilic benthic species belonging to genus Fragilaria sensu lato dominated. The second group included shallow, moderately acidified lakes, where acidophilous diatoms (Eunotia glacialis, E. exigua and Tabellaria flocculosa) were most abundant.