Spatial distribution of environmental indicators in surface sediments of Lake Bolshoe Toko, Yakutia, Russia

Abstract

Abstract. Rapidly changing climate in the Northern Hemisphere and associated socio-economic impacts require reliable understanding of lake systems as important freshwater resources and sensitive sentinels of environmental change. To better understand time-series data in lake sediment cores, it is necessary to gain information on within-lake spatial variabilities of environmental indicator data. Therefore, we retrieved a set of 38 samples from the sediment surface along spatial habitat gradients in the boreal, deep, and yet pristine Lake Bolshoe Toko in southern Yakutia, Russia. Our methods comprise laboratory analyses of the sediments for multiple proxy parameters, including diatom and chironomid taxonomy, oxygen isotopes from diatom silica, grain-size distributions, elemental compositions (XRF), organic carbon content, and mineralogy (XRD). We analysed the lake water for cations, anions, and isotopes. Our results show that the diatom assemblages are strongly influenced by water depth and dominated by planktonic species, i.e. Pliocaenicus bolshetokoensis. Species richness and diversity are higher in the northern part of the lake basin, associated with the availability of benthic, i.e. periphytic, niches in shallower waters. δ18Odiatom values are higher in the deeper south-western part of the lake, probably related to water temperature differences. The highest amount of the chironomid taxa underrepresented in the training set used for palaeoclimate inference was found close to the Utuk River and at southern littoral and profundal sites. Abiotic sediment components are not symmetrically distributed in the lake basin, but vary along restricted areas of differential environmental forcing. Grain size and organic matter are mainly controlled by both river input and water depth. Mineral (XRD) data distributions are influenced by the methamorphic lithology of the Stanovoy mountain range, while elements (XRF) are intermingled due to catchment and diagenetic differences. We conclude that the lake represents a valuable archive for multiproxy environmental reconstruction based on diatoms (including oxygen isotopes), chironomids, and sediment–geochemical parameters. Our analyses suggest multiple coring locations preferably at intermediate depth in the northern basin and the deep part in the central basin, to account for representative bioindicator distributions and higher temporal resolution, respectively.

Lake-depth related pattern of genetic and morphological diatom diversity in boreal Lake Bolshoe Toko, Eastern Siberia

“…Our study detects a strong relationship between intra-lake diatom diversity and water depth variation within the big glacial Lake Bolshoe Toko as suggested by [38]. Alpha and beta diversity estimates based on morphological investigations have a negative correlation with water depth.…”

“…The similarity found in our study is most prominent in the local contribution to beta diversity (LCBD). Both approaches reveal the uniqueness of the same three localities, one close to the northern shore of Lake Bolshoe Toko and the others from the lagoon, a part which is gradually becoming separated from the main basin of the lake, putatively explaining their peculiarity [38]. We conclude that despite the differences in alpha diversity and the taxonomic assignment of both morphological and phylogenetic approaches, beta diversity displays a more similar intra-lake diatom community pattern in Lake Bolshoe Toko.…”

“…Unfrozen zones (taliks) beneath deep lakes such as Lake Bolshoe Toko are believed to reach the permafrost base [37]. Recently, a small lagoon on the eastern shore of the lake is gradually becoming separated from the main basin, presumably due to increasing temperature and lake level decrease [38]. According to [39] Lake Bolshoe Toko, as compared to all other investigated lakes in the study, is the deepest lake in Yakutia.…”

“…Short sediment cores of up to ca. 40 cm length were retrieved at multiple sites within the lake, using a UWITEC gravity corer [38]. Sediment cores were immediately subsampled after retrieval in the field for DNA analyses.…”

“…Perhaps this variance could be attributed to nutrient variability in, for example, total organic carbon (TOC) and total nitrogen (TN). Changes in TOC/TN ratio, as detected by [38], indicate the relative influx of land and water plants [77] and might lead to higher nutrient contents at river entries [70].…”