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\nsocio-economic impacts require reliable understanding of lake systems as\nimportant freshwater resources and sensitive sentinels of environmental\nchange. To better understand time-series data in lake sediment cores, it is\nnecessary to gain information on within-lake spatial variabilities of\nenvironmental indicator data. Therefore, we retrieved a set of 38 samples\nfrom the sediment surface along spatial habitat gradients in the boreal,\ndeep, and yet pristine Lake Bolshoe Toko in southern Yakutia, Russia. Our\nmethods comprise laboratory analyses of the sediments for multiple proxy\nparameters, including diatom and chironomid taxonomy, oxygen isotopes from\ndiatom silica, grain-size distributions, elemental compositions (XRF),\norganic carbon content, and mineralogy (XRD). We analysed the lake water for\ncations, anions, and isotopes. Our results show that the diatom assemblages\nare strongly influenced by water depth and dominated by planktonic species,\ni.e. Pliocaenicus bolshetokoensis. Species richness and diversity are higher in the northern part of the\nlake basin, associated with the availability of benthic, i.e. periphytic,\nniches in shallower waters. δ18Odiatom values are higher\nin the deeper south-western part of the lake, probably related to water\ntemperature differences. The highest amount of the chironomid taxa\nunderrepresented in the training set used for palaeoclimate inference was\nfound close to the Utuk River and at southern littoral and profundal sites.\nAbiotic sediment components are not symmetrically distributed in the lake\nbasin, but vary along restricted areas of differential environmental forcing.\nGrain size and organic matter are mainly controlled by both river input and\nwater depth. Mineral (XRD) data distributions are influenced by the\nmethamorphic lithology of the Stanovoy mountain range, while elements (XRF)\nare intermingled due to catchment and diagenetic differences. We conclude\nthat the lake represents a valuable archive for multiproxy environmental\nreconstruction based on diatoms (including oxygen isotopes), chironomids, and\nsediment–geochemical parameters. Our analyses suggest multiple coring\nlocations preferably at intermediate depth in the northern basin and the\ndeep part in the central basin, to account for representative bioindicator\ndistributions and higher temporal resolution, respectively.