Assessing arctic flora composition in the Siberian treeline ecotone by vegetation mapping, pollen analyses and sedimentary DNA metabarcoding

Arctic environments are one of the most climatically influenced areas worldwide. These influences are currently causing major changes in vegetation composition, for example in the Taymyr lowlands, which harbour the northernmost boreal-arctic treeline areas of the world. The most dominant species of the treeline ecotone in this region are Larix gmelinii, Betula nana and Alnus viridis. They are presently shifting in density and range, and have done so multiple times throughout the Holocene. To understand the vegetation changes it is necessary to investigate the current state, before deducing changes for other time phases of the Holocene. To this end a field campaign was carried out at the Taymyr lowlands in 2013 to perform a multidisciplinary investigation by combining methods from vegetation mapping, palynological records and sedimentary DNA metabarcoding. We sampled lake sediments and mapped the vegetation along a transect spanning the treeline ecotone, with changing vegetation composition and density. Our results of the surveyed vegetation will help to investigate the current state of vegetation and will also be used as calibration of the pollen and DNA metabarcoding records. The comparison of the vegetation and pollen record will allow the assessment of over- or underrepresentation of certain taxa within the pollen signal, and this will enable a more secure interpretation of historic pollen records. We will also test this for the DNA metabarcoding data, which has not yet been systematically done for lake sediments in arctic latitudes. This multidisciplinary investigation will draw a more comprehensive image of the current vegetation composition at the Taymyr lowlands than has been possible to date, and will enable a more secure interpretation of historical vegetation change in this highly dynamic area

Preliminary studies of zooplankton communities and assesment of the ecological status of lake suturuokha (Ne Siberia, Russia)

© SGEM2017. Lake Suturuokha (69'06 "N, 145'23" E) is a unique lake within the Indigirka River basin, which is located on the border of the forest-tundra and taiga in the north of the Republic of Sakha (Yakutia). Formed due to the influence of glaciers of several glaciations in the late Pleistocene, the lake has a large area (69 km 2 ) and comparatively shallow depths (2 - 2.5 m). Because of its unusual genesis and low study, the lake is of great interest to scientists. In August 2015, in the framework of the research expedition, an assessment of the current ecological conditions of Lake Suturuokha was implemented, in the course of which hydro-biological samples were selected from 16 different points located in different biotopes of the lake’s water area. According to the research conducted, Lake Suturuokha can be referred to as highly productive due to the active blooming blue-green and green algae and a mass accumulation of effipium of Daphnia middendorffiana (Fischer, 1851), Cladocera. 53 species and forms in species diversity of zooplankton community were revealed; of these, 31 were Rotifera, 12 Cladocera and 11 Copepoda. High frequency indicators belonged to the rotifers Brachionus angularis (Gosse, 1851), Collotheca pelagica (Rousselet, 1893), Kellicotia longispina (Kellicot, 1879), as well as the cladocera Daphnia middendorfiana (Fischer, 1851) and the juvenile Copepoda. 76.6 % of the total zooplankton abundance included rotifers, 21.7 % and 1.7 % of the abundance involved Copepod and Cladocera. The average value of the zooplankton abundance of the lake was 35.10 thousand ind./m 3 . Biomass of zooplankton of the lake Suturuokha on the average had a value of 295.2 mg/m 3 . 64.1 % of it were Cladocera, especially large D. middendorfiana. 36.7 % of the biomass contained Copepoda, 1.7 % - of rotifer biomass. Mass clusters of Cladocera efippia, formed primarily by D. middendorphiana, were discovered. Estimators of Shannon’s index and saprobity index defined that the lake was located on the border to pure and moderately polluted waters and had oligosaprobic level (the average values 2.57 and 1.47 accordingly). The prevalence of littoral species (44 %) and cosmopolitan species (53 %) in zooplankton was explained by the small depths of the lake. However, quantitatively, the dominant structure of zooplankton was cold-water species

Species composition of planktonic algae of termokarst lakes of Khatanga River Basin (Krasnoyarsk Region, Russia)

Objective of this study was to determine the species composition of modern planktonic algae in the range of thermokarst lakes of Khatanga River basin (Krasnoyarsk region, Russia). The Khatanga River flows in the North-Siberian lowland in the south-eastern part of the Taimyr Peninsula and flows into the Khatanga Gulf of the Laptev Sea. The river basin has about 112 thousand lakes with a total area of 12 thousand sq.km. Today, M.K. Ammosov North-Eastern Federal University (Yakutsk), A. Wegener Institute for Marine and Polar Research (AWI, Potsdam, Germany), and Kazan Federal University has entered into agreement on cooperation in the sphere of science and higher professional education. In the framework of this agreement, in August 2013, an expedition was conducted to study the limnological characteristics of the lakes in Yakutia in order to reconstruct the Holocene history, during which the algological water samples from and hydro-chemical and morphometric data on 18 lakes were obtained. During the observation period, we found 164 algae taxa belonging to 6 different groups in phytoplankton of the investigated water bodies. The greatest number of taxa were identified in the groups of diatoms and chlorococcaceae. According to the ecological and geographical characteristics, the dominant species in these lakes are cosmopolitan and boreal algae. In relation to halobility, most species are indifferent and oligohalobic, and in terms of pH the most common are the indifferent and alkaliphile + alkalibiontic organisms

PALAEOENVIRONMENTAL MESSAGES FROM MOUNTAIN LAKES OF EASTERN SIBERIA

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Holocene climate conditions in central Yakutia (Eastern Siberia) inferred from sediment composition and fossil chironomids of Lake Temje

A 380 cm long sediment core from Lake Temje (central Yakutia, Eastern Siberia) was studied to infer Holocene palaeoenvironmental change in the extreme periglacial setting of eastern Siberia during the last 10,000 years. Data on sediment composition were used to characterize changes in the depositional environment during the ontogenetic development of the Lake Temje. The analysis of fossil chironomid remains and statistical treatment of chironomid data by the application of a newly developed regional Russian transfer functions provided inferences of mean July air temperatures (TJuly) and water depths (WD). Reconstructed WDs show minor changes throughout the core and range between 80 and 120 cm. All the fluctuations in reconstructed water depth lie within the mean error of prediction of the inference model (RMSEP = 0.35) so it is not possible to draw conclusions from the reconstructions. A qualitative and quantitative reconstruction of Holocene climate in central Yakutia recognized three stages of palaeoenvironmental changes. The early Holocene between 10 and 8 ka BP was characterized by colder-than-today and moist summer conditions. Cryotextures in the lake sediments document full freezing of the lake water during the winter time. A general warming trend started around 8.0 ka BP in concert with enhanced biological productivity. Reconstructed mean TJuly were equal or up to 1.5 °C higher than today between 6.0 ka and 5.0 ka BP. During the entire late Holocene after 4.8 ka BP, reconstructed mean TJuly remained below modern value. Limnological conditions did not change significantly. The inference of a mid-Holocene climate optimum supports scenarios of Holocene climatic changes in the subpolar part of eastern Siberia and indicates climate teleconnections to the North Atlantic realm. © 2012 Elsevier Ltd and INQUA

Limnological characteristics of lakes in the lowlands of Central Yakutia, Russia

The physico-chemical characteristics of 47 lakes from two regions in the lowlands of Central Yakutia (Vilyuysk and Yakutsk), Eastern Siberia were analysed. The aims of this study were (i) to classify the lakes according to their ionic compositions and their nutrient concentrations, (ii) to quantify environmental gradients representing the main directions of variation in the measured variables, and (iii) to explore the relationship between the investigated lakes and their spatial positions. Most of the study lakes are shallow, thermokarst lakes that are slightly alkaline to alkaline. The lakes are predominantly oligotrophic, with some mesotrophic and a few eutrophic exceptions in the study region Vilyuysk. There are four hypertrophic lakes in the study region Yakutsk which are strongly affected by anthropogenic inputs and, in one case, additionally by inputs of water birds. Most part of the variance in the data is represented by major ion concentrations and related variables such as electrical conductivity. There were clear differences in these variables between the lakes of both study regions partly due to regional differences in the climate-induced negative water balance (i.e. evaporation exceeds precipitation). The statistical analysis has shown that a significant part of the variance can be attributed to the type of vegetation in the lake's catchment (11%), to the longitude (7.6%) and to local spatial differences in the lake water chemistry (2.8%). Hypothesis testing indicated that there are significant differences in the mean values of many variables according to vegetation type and to the region where the lakes are located. However, the hypothesis of spatial autocorrelation in the data had to be rejected. The results presented here have important implications for ongoing and future limnological and paleoenvironmental studies in Yakutia. The exploratory analysis has shown that the physico-chemical characteristics of Central Yakutian lakes are mainly influenced by vegetation and climate driven changes that provides the basis for paleoenvironmental studies

Genetic and morphologic determination of diatom community composition in surface sediments from glacial and thermokarst lakes in the Siberian Arctic

Lakes cover large parts of the climatically sensitive Arctic landscape and respond rapidly to environmental change. Arctic lakes have different origins and include the predominant thermokarst lakes, which are small, young and highly dynamic, as well as large, old and stable glacial lakes. Freshwater diatoms dominate the primary producer community in these lakes and can be used to detect biotic responses to climate and environmental change. We used specific diatom metabarcoding on sedimentary DNA, combined with next-generation sequencing and diatom morphology, to assess diatom diversity in five glacial and 15 thermokarst lakes within the easternmost expanse of the Siberian treeline ecotone in Chukotka, Russia. We obtained 163 verified diatom sequence types and identified 176 diatom species morphologically. Although there were large differences in taxonomic assignment using the two approaches, they showed similar high abundances and diversity of Fragilariceae and Aulacoseiraceae. In particular, the genetic approach detected hidden within-lake variations of fragilarioids in glacial lakes and dominance of centric Aulacoseira species, whereas Lindavia ocellata was predominant using morphology. In thermokarst lakes, sequence types and valve counts also detected high diversity of Fragilariaceae, which followed the vegetation gradient along the treeline. Ordination analyses of the genetic data from glacial and thermokarst lakes suggest that concentrations of sulfate, an indicator of the activity of sulfate-reducing microbes under anoxic conditions, and bicarbonate, which relates to surrounding vegetation, have a significant influence on diatom community composition. For thermokarst lakes, we also identified lake depth as an important variable, but sulfate best explains diatom diversity derived from genetic data, whereas bicarbonate best explains the data from valve counts. Higher diatom diversity was detected in glacial lakes, most likely related to greater lake age and different edaphic settings, which gave rise to diversification and endemism. In contrast, small, dynamic thermokarst lakes are inhabited by stress-tolerant fragilarioids and are related to different vegetation types along the treeline ecotone. Our study demonstrated that genetic investigations of lake sediments can be used to interpret climate and environmental responses of diatoms. It also showed how lake type affects diatom diversity, and that such genetic analyses can be used to track diatom community changes under ongoing warming in the Arctic