ИСТИНА

Diatom associations from surface 0-1 cm layer of bottom sediments of small meromictic lake located on Karelia Coast of White Sea were examined. High absolute numbers of diatoms valves and chrysophyte cysts were revealed for all stations. C/D index is low in shallow part of lake and significantly increase on stations localized below the boundary of anoxic bottom water. Diatom associations characterized by a good averaging over the lake area and the unity of the composition of dominants and subdominants in all samples despite the sharp environmental gradients. Benthic and meroplankton species are absolutely dominated, while holoplankton has low diversity and rare occurrence. Mass occurrence is revealed for three small colonial species of the family Fragilariaceae: Stauroforma exiguiformis (Lange-Bertalot) Flower & Jones, Fragilaria sopotensis Witkowski & Lange-Bertalot, Pseudostaurosira sp. Subdominants are halophilic and mesohaline species (Ctenophora pulchella (Ralfs ex Kützing) D.M. Williams & Round, Amphora copulata (Kützing) Schoeman & Archibald, Mastogloia smithii Thwaites, Navicula rhynchotella Lange-Bertalot, Ulnaria danica (Kützing) Compère & Bukhtiyarova and other) on all stations including shallow freshwater area of lake.