RESEARCH OF THE ISOETID OLIGOTROPHIC LAKES IN TVER REGION: PHOTOSYNTHETIC BIOTA AS THEIR TROPHIC STATE INDICATOR
Relevance and goals. The extreme vulnerability of isoetid oligotrophic lakes as habitats of rare and even relict macrophytes (including Lobelia dortmanna) to substantial deterioration (especially to eutrophication) considerably actualizes the study of a trophic state in some Tver region lakes (including Bel'skoe lake and Kolomenskoe lake) by means of bioindication methods due to data inconsistency. Materials and methods. In 2015-2016 we studied water plants, cyanoprocaryotes and algae (macro- and microphytes) in these two lakes (taking photos, counting species, collecting and germinating seeds, morphology and anatomy analysis) with a special relevance to some littoral locus in population of Lobelia dortmanna as well as collected stoneworts Chara virgata (=Ch. delicatula) and Ch. fragifera at the shallow of Bel'skoe lake. Results. The published data on similarity of trophic status in both lakes and absence of a connection between them via channel is not true. Water from Bel'skoe lake moves to the Kolomenskoe lake via narrow channel and sometimes (as it was in August 2016) reveals noticeable current and thus provides communication between the lakes but there is obvious difference in their trophic status: Bel'skoe is an oligotrophic lake and Kolomenskoe is a eutrophic lake. The protection status of the former must be raised to the Federal level. Conclusions. A proved presence of some endangered vulnerable species ( Lobelia dortmanna, stoneworts Chara virgata and Ch. fragifera, rare cyanoprocaryotic epiphyte Gloeotrichia pisum etc.) among phototroph biota must serve as a ground for organizing permanent monitoring of Bel'skoe lake trophic state as a unique ecosystem in the region. Lobelia population state can be recognized as relatively stable by taking into account its density, seed reproduction ability and its influence on oxygen regime at the lake bottom. But it seems reasonable to raise protection status of Lobelia to 2/EN as in adjacent Vologda region. Using endangered and disappearing stoneworts species as indicators of maintaining eutrophication in Bel'skoe lake will help to gain a better understanding of the biological and environmental conditions defining conservation of such unique shallow oligotrophic lakes.