CLADOCERA COMMUNITIES OF LAKE ARCTO-PIMBERTO (NENETS AUTONOMOUS DISTRICT) IN THE MIDDLE AND LATE HOLOCENE<a href="#FN1">¹</a>

Abstract

The analysis of the subfossil Cladocera community in the bottom sediments from Lake Arcto-Pimberto located in the Pechora River delta (Nenets Autonomous District) was carried out. A 95-cm-long continuous core of bottom sediments was collected in the deepest part of the lake and covers approximately 6400 years of sediment accumulation during Middle and Late Holocene. 17 cladoceran taxa were identified in the studied core. Species with Holarctic and Palearctic distributions prevailed in the lake. Most of the identified subfossil remains belong to pelagic species living in the open part of the lake. Found fragments of chitinized remains of Rhynchotalona falcata and Alonopsis elongata indicate the presence of sandy soils in the water body. The samples were dominated by Bosmina (Eubosmina) longispina and Chydorus cf. sphaericus, which are evenly distributed along the continuous sediment core. We have studied the history of the development and evolution of the lake based on changing of the taxonomic composition of microcrustaceans in the bottom sediment core. The structure of the subfossil Cladocera community stayed relatively constant. The ratio of pelagic and littoral-phytophilic taxa changed slightly. Depending on the changes in the species composition of the cladoceran assemblage, the sediment core was divided into 4 ecological zones. In the early history of sedimentation in the lake, there is a small peak in the abundance of crustaceans, followed by decrease and further gradual increase towards the upper horizons of the column. Between from 5700 cal. years BP to 2100 cal. years BP there is an increase in abundance of pelagic organisms, with a decrease in abundance of littoral taxa. This marks the presence of a well-developed pelagic part of the reservoir at that time. In the upper zones, we observe the taxonomic diversity of littoral organisms and an increase in abundance of their remains. The Shannon-Weaver species diversity Index showed a simple organization of the community of subfossil Cladocera. The Pantle and Buck saprobity Index characterized the lake as oligosaprobic, this status is maintained throughout its evolution of the lake.