Phytoplankton in mountain lakes of Eastern Siberia

The paper presents a study of species composition, structure features, and phytoplankton number and biomass in mountain lakes of Pribaikalie (the area westward from Lake Baikal), Zabaikalie (the area correspondingly eastward from Lake Baikal), and the southern part of Yakutia. About 70 large and small lakes, located in the Khamar-Daban, eastern Sayan, Kodar, Udokan, Kalarsky, and Baikalian ridges at altitudes of 330 to 1900 m and sometimes higher, have been researched. The largest of them is the lake Oron-Vitimsky. Their plankton algoflora is presented by 196 taxa lower than genus from 7 phyla. Two genera, Dinobryon of 15 taxa and Aulacoseira of 13 ones, are the most diverse. The baikalian endemic diatoms A. baicalensis (K. Meyer) Sim., Cyclotella baicalensis, C. minuta, Stephanodiscus meyeri, and spore-forming A. islandica (this form of the alga is known to dwell in the lake Khanka and the river Amur, Far East, only), as well as dinoflagellate Gymnodinium baicalense var. minor, have been found there. In most lakes, the relict alga Pliocaenicus costatus, wide-spread in ancient times from Europe to the Kamchatka peninsula, has been observed also. All the lakes are oligotrophic almost round the year exhibiting phytoplankton biomass of 30 to 200 mgЧm-3. At their maximal seasonal development, these values in the open part of the lakes reached 300 mgЧm-3, sometimes higher, and 800 mgЧm-3 in shallows. Their seasonal dynamics displays three biomass maxima: winter, spring, and autumn.