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Relative abundance (%) of diatom taxa in the assemblages gained from morphological identification. Total species richness and valve concentration are given on the right-hand side before the Holocene zonation for the core (EH: Early Holocene, MH: Mid-Holocene, LH: Late Holocene). Blue bars indicate planktonic diatoms, green bars indicate epiphytic diatoms, and brown bars indicate benthic diatoms. Note the different scales of relative abundance
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In Central Yakutia (Siberia) livelihoods of local communities depend on alaas (thermokarst depression) landscapes and the lakes within. Development and dynamics of these alaas lakes are closely connected to climate change, permafrost thawing, catchment conditions, and land use. To reconstruct lake development throughout the Holocene we analyze sedi...
Citations
... Each element produces a unique set of characteristic fluorescent X-rays. Qualitative and quantitative analyses.Braadbaart et al., 2020;Capo et al., 2021;Baisheva et al., 2023 X-ray Diffraction (XRD) Determines the physical properties such as crystal structure and orientation.Frouin et al., 2013;Braadbaart et al., 2020;Kanbar et al., 2020; Jelavić et al., 2023 Inductively Coupled Plasma Mass Spectrometry (ICPMS) ...
Caves are unique depositional environments that hold great potential for long‐term preservation of DNA due to their typically cool and stable internal climates, buffered from external climate extremes. Bones from caves have long been recognised as an excellent source of ancient DNA, yet the potential for DNA preservation in cave sediments themselves has only recently begun to be explored. Here, we discuss features of caves that make them well‐suited to the long‐term preservation of sedimentary ancient DNA (sedaDNA), focussing specifically on sources, taphonomy and preservation of cave sedaDNA. We also highlight opportunities for future work to improve our understanding of the processes influencing long‐term DNA preservation within cave sediments. These recommendations seek to improve our understanding of sedimentary ancient DNA taphonomy within caves and enhance the level of insights about the past that can be gained from it and include: (1) designation of reference sections and sample repositories; (2) routine collection of sediment, mineralogy and geochemistry data; (3) routine collection of cave climate data; (4) increased application of microstratigraphic and spatial analyses; (5) advocating use of multiple proxies when interpreting results and (6) ensuring ethical best practices are followed.
... At Lake Satagay, a late-stage thermokarst lake (Baisheva et al., 2023), the Holocene charcoal record displays a pronounced maximum at ca. 10 000 BP and suggests the establishment of the modern (preindustrial) fire regime around 4500 BP. Combination with data on terrestrial plants from sedimentary ancient DNA and quantitative vegetation cover based on a pollen record highlights a potential relationship Figure 1. ...
[Thesis abstract]
Recent intense wildfire seasons in the circumpolar boreal forests raise questions regarding drivers and impacts of past fire regime changes. Charcoal in lake sediments is commonly used to reconstruct past trends of biomass burning. However, eastern Siberia is poorly covered by such data. Considering the unique larch-dominated forests and their climate-sensitive relationships with permafrost and fire, both affected by ongoing climatic warming, this lack of data presents a key research gap.
By applying both paleo-ecological and modeling methods, this dissertation evaluates (I) wildfire dynamics of the past ca. 20 000 years, (II) relationships between fire regime changes and larch forest structure, and (III) the potential human dimension of past fire regime changes in the Republic of Sakha (Yakutia). [...]
... 整体而言，北极热融湖的发育可分为初始形成、中期扩张和晚期干涸3个阶段。其 中，促使热融湖形成的关键驱动要素因其发育环境不同而存在一定差异 (图5a) 。例如， 广泛分布于苔原或北方低地的热融湖 [43,[64][65][66] ，其形成过程通常与富冰多年冻土退化及厚层 地下冰融化所导致的地面沉降、塌陷和排水量增加有关 [26,[67][68][69] 。然而，对于冰川较为发育 的多年冻土区而言，热融湖的形成还与冰川冰和沉积物内冰的融化密切相关 [70] ，对于地 下冰楔发育等地区，当地表存在如森林火灾或暴雨引起的植被破坏，以及上覆泥炭层破 裂导致的冰楔出露等能量扰动时，也会进一步促使热融湖的形成和发育 [71] 。此外，对于 多年冻土不发育的地区，当其地下水位较浅且广泛分布渗透率较低的泥炭地时，也可能 导致形成热融湖 (例如西伯利亚西部部分地区) [44] 。 在随后的扩张和干涸阶段，热融湖的湖盆形态和水热条件均发生显著变化 (图5b5 c) 。以勒拿河三角洲苔原低洼地带的热融湖为例 [50] ，在早期苔原多边形发展成为热融湖 后，进入中期扩张期，进一步在横向和纵向上持续扩张并在热融湖底部发生沉积作用， 该阶段的热融湖下方易形成深层融区，直至湖盆底部含冰复合沉积物 (Ice Complex Deposits) 完全融化时，热融湖开始仅发生横向上的扩张；在此之后，受地表水渗漏等作 用的影响，热融湖面积缩小、水体变浅并进入晚期干涸阶段，该阶段常伴随部分出露湖 底沉积物和融区的再次冻结，并在湖盆下方形成更为复杂的含冰复合体。 热融湖的发展受气候变化、多年冻土条件、水文过程、地形地貌以及土地覆盖状况 等多种因素的综合影响 [72][73][74] 。总体上，这些因素主要通过水量和水热两大驱动机制对热融 湖产生影响。就水量而言，气候变化通过改变降水、蒸发、径流以及积雪/多年冻土融水 等水文要素，在局地尺度上直接影响着热融湖的变化趋势。例如，2002-2015年格陵兰 岛西南部地区由于蒸发量增加，使得康埃卢苏阿克附近的局地热融湖总面积整体呈减小 趋势，而在西西缪特海岸附近，受局地降水量显著增加的影响，热融湖面积反而呈增加 趋势 [75] ；尽管降水对热融湖变化的影响存在一定时滞效应 [16] ，但整体上高降水量年份通 7.14 常伴随着热融湖的显著扩张 [64] ；此外，一定量的积雪融水也会促进热融湖的扩张，但过 量的融水则可能引起热融湖的快速排水和萎缩 [76] 。在水热条件方面，冻融过程是引起北 极热融湖变化的关键因素，多年冻土的初期融化往往伴随着热融湖面积的增加，而持续 的升温则会导致进一步的融化，最终使热融湖面积减少 [46] 。一方面，热侵蚀和物理侵蚀 作用会促使热融湖扩大并与相邻水体合并，形成更大的热融湖，尤其是在冰川发育的多 年冻土区 [70] 。另一方面，异常温暖的年份加剧了热侵蚀作用，导致热融湖频繁排水，从 而减少热融湖水量 [39,77] 。值得注意的是，随着多年冻土退化，尤其是当热融湖下方深层 融区穿透多年冻土层时 [78] ，热融湖更易因地下水渗漏而发生萎缩甚至完全干涸 (图5c) 。 因此，热融湖的动态变化与其发育阶段、深层融区形成程度、浅层含水层渗透性、冻融 状态等因素紧密相关 [44,79] 。这一热融湖萎缩的关键机制已经通过地球物理勘测方法 (如 探地雷达 (GPR) 和直流电阻率法 (DC)) 在阿拉斯加部分不连续多年冻土区域的热融 湖研究中得到了证实 [78][79] 。除此之外，近年来北极地区频繁发生的极端高温和极端降水事 件也是影响热融湖变化的关键性因素之一，并通过加剧热侵蚀作用和改变水量而引起热 融湖的突发性排水事件，进而改变热融湖的规模和数量 [76,80] 。这些北极气候及陆地环境 的变化均会影响北极地区的可持续发展 [25,[81][82] ...
... The aquatic vegetation types recorded in the surface sediments are comparable or even superior to the in-lake vegetation surveys when comparing the surface sediment DNA (sedDNA) with the in-lake vegetation survey data (Alsos et al., 2018). Recent studies employing sedaDNA for reconstructing aquatic macrophyte compositions have provided invaluable insights into their historical biological structure and function change (Baisheva et al., 2023;Karachurina et al., 2023). However, despite the TP having the largest group of alpine lakes in the world (Wang and Dou, 1998), the application of sedaDNA technology has been limited to terrestrial plant reconstruction and diversity studies Liu et al., 2021aLiu et al., , 2021b, neglecting its potential in aquatic macrophyte research. ...
Understanding the response of long-term aquatic environmental changes in lakes to ongoing climate change and human activities is key to forecasting future lake conditions. In this study, we infer the Holocene limnological changes in Emu Co, a proglacial lake in Nianbaoyuze on the eastern Tibetan Plateau, from sedimentary ancient DNA (sedaDNA) data, and palynomorph, element, lithological, and grain-size analyses. We developed a transfer function based on Siberia and Tibet/China surface sedimentary DNA and applied it to Emu Co sedaDNA to trace lake conductivity changes. The results show that the conductivity of Emu Co was high during 12.6− 9.7 cal ka BP, often surpassing 1000 μs cm − 1 , driven by elevated summer solar radiation. The freshwater influx from glacial meltwater and precipitation, however, reduced the lake's conductivity as the climate warmed and humidified. This led to a decrease in the abundance of taxa characterised by high conductivity. Freshwater pulses, triggered by climatic fluctuations, likely led to significant variations in conductivity within the overarching downward trend. By 8 cal. ka BP, lake recharge conditions stabilised and conductivity reached a lower level of~70 μs cm − 1. The warm and humid mid-Holocene (8− 5 cal. ka BP) provided suitable habitat conditions for many submerged freshwater taxa. After 5 cal. ka BP, the growth of submerged taxa was restricted, as indicated by a shift from asexual to sexual reproduction in macrophytes, likely in response to suboptimal conditions of a colder and drier climate. Since 1 cal. ka BP, human activities might have increased lake nutrient levels, with an enhanced richness of macrophytes. Our results indicate how millennial-scale hydrological changes in a lake are related to glacial retreat and catchment changes in the alpine region of the Tibetan Plateau, which is today facing climate change much greater than the global average.
... PCR was performed with the "g" and "h" universal plant primers for the P6 loop region of the chloroplast trnL (UAA) intron (Taberlet et al., 2007). PCR setup followed the protocol of Baisheva et al. (2023). We produced three PCR replicates for sediment samples and DNA extraction controls and added a PCR negative template control (NTC) in each PCR replicate batch. ...
Climate seasonality critically influences the functioning and dynamics of ecosystems in continental areas. The ecological importance of winter temperatures on high-latitude vegetation changes has recently been argued to be largely overlooked in comparison to summer temperatures. The Oymyakon region from eastern Siberia, with its strong continentality of extremely cold winters and moderately warm summers, is ideally suited to study the response of past vegetation to seasonal temperature changes based on long ecological time-series. However, few paleorecords are available from this area. The history of regional glacial activity and potential plant refugia since Marine Isotope Stage (MIS) 3 is not well understood. Here, we present geochemical and plant DNA metabarcoding records retrieved from a sediment core from Lake Ulu in the Oymyakon region, which provides detailed information on glacier and vegetation dynamics over the last 43 cal. ka BP. Our results suggest that glacial fluctuations were primarily driven by summer insolation, and Lake Ulu was likely initiated by glacial retreat during MIS 3. The catchment experienced multiple glacial advance/retreat cycles until the Last Glacial Maximum, and the glaciers fully retreated by 20 cal. ka BP. In addition, a tundra-steppe landscape dominated by Dryas, Papaver, Saliceae, and Anthemideae occupied the catchment for most of the time and began to collapse around 19 cal. ka BP following the expansion of trees and shrubs such as Larix, Betula, Alnus, and Vaccinium. Postglacial plant assemblages in the Oymyakon region exhibit a high sensitivity to summer temperature variations, with minimal impact from winter temperatures. This can be explained by the dominance of summer insolation amplitude, extreme continentality, extended plant growing season, and plant genetic adaptation to cold. Notably, our ancient DNA record show the earliest postglacial expansion of larch in eastern Siberia (around 18.6 cal. ka BP), which is likely related to the presence of local refugia. This implies that the Oymyakon region may be one of the earliest sources for larch recolonization and that more research should be implemented to provide insights into larch expansion and migration, and to better predict the future scenarios for Siberian larch forests.
... The thermokarst lake, formed during the Late Glacial (between the Last Glacial Maximum and the Holocene, c. 20,000 to 11,700 ka BP), was analyzed to obtain records of both lake development stages and lake ecology (Baisheva et al. 2023), as well as surrounding vegetation and wildfire activity (Glückler et al. 2022) throughout the past c. 10,800 years. ...
Background: Wildfires are recognized as an important ecological component of larch-dominated boreal forests in eastern Siberia. However, long-term fire-vegetation dynamics in this unique environment are poorly understood. Recent paleoecological research suggests that intensifying fire regimes may induce millennial-scale shifts in forest structure and composition. This may, in turn, result in positive feedback on intensifying wildfires and permafrost degradation, apart from threatening human livelihoods. Most common fire-vegetation models do not explicitly include detailed individual-based tree population dynamics, but a focus on patterns of forest structure emerging from interactions among individual trees may provide a beneficial perspective on the impacts of changing fire regimes in eastern Siberia. To simulate these impacts on forest structure at millennial timescales, we apply the individual-based, spatially explicit vegetation model LAVESI-FIRE, expanded with a new fire module. Satellite-based fire observations along with fieldwork data were used to inform the implementation of wildfire occurrence and adjust model parameters.
Results: Simulations of annual forest development and wildfire activity at a study site in the Republic of Sakha (Yakutia) since the Last Glacial Maximum (c. 20,000 years BP) highlight the variable impacts of fire regimes on forest structure throughout time. Modeled annual fire probability and subsequent burned area in the Holocene compare well with a local reconstruction of charcoal influx in lake sediments. Wildfires can be followed by different forest regeneration pathways, depending on fire frequency and intensity and the pre-fire forest conditions. We find that medium intensity wildfires at fire return intervals of 50 years or more benefit the dominance of fire-resisting Dahurian larch (Larix gmelinii (Rupr.) Rupr.), while stand-replacing fires tend to enable the establishment of evergreen conifers. Apart from post-fire mortality, wildfires modulate forest development mainly through competition effects and a reduction of the model’s litter layer.
Conclusion: With its fine-scale population dynamics, LAVESI-FIRE can serve as a highly localized, spatially explicit tool to understand the long-term impacts of boreal wildfires on forest structure and to better constrain interpretations of paleoecological reconstructions of fire activity.
... The main conclusions so far are that local environmental variables including water temperature, nutrient concentrations, pH, and predation by zooplankton grazers influence the distribution of eukaryotic phytoplankton. Some studies have further compared sedDNA with water monitoring (Thorpe et al., 2023) or classical diatom subfossil analyses (e.g., Anslan et al., 2022;Baisheva et al., 2023;Huang et al., 2020), highlighting that classical and molecular methods are generally similar but differences can arise in diversity and taxonomy. Beyond the potential to identify taxa that do not preserve in the fossil record, sedDNA also offers the opportunity to investigate intraspecific genomic variability . ...
Ecosystems are continuously responding to both natural and anthropogenic environmental change. Lake sediments preserve local and global evidence of these ecological transitions through time. This archived information can yield crucial insights through the reconstruction of past changes over hundreds to many thousands of years. This chapter provides an overview on what lake sedimentary DNA (sedDNA) is, which biological groups can be detected with this novel paleoecological proxy, and the workflow and analytical techniques currently employed in sedDNA research. Finally, the implications of lake sedDNA studies are illustrated through five topics, illustrating how sedDNA can reconstruct lake response to environmental change.
Arctic and subarctic regions face rapid warming and environmental changes. Freshwater ecosystems and their watersheds in the region are at risk of being increasingly impacted and significantly altered. The majority of lakes in the Republic of Sakha (Yakutia), eastern Siberia, are thermokarst lakes, the origin of which is defined by the harsh climate of the past and geographic locations of lowlands and plains on permafrost, which contain alaas landscapes. Alaases, non-forested permafrost basins that often feature a lake, provide not only important aquatic habitats for biodiversity, but also critical ecosystem services to local populations such as fresh water supply, recreation, cattle breeding, fishing, and hunting grounds. Although most of these lakes found in alaases are of shallow depth and cover a small lake surface area, they are predicted to undergo severe changes with continued climate change. However, data on sequential lake development and distribution in Yakutia is still scarce. This thesis aims to improve the understanding of lake development in Yakutia since the last glaciation, including the unique alaas lakes, by studying their aquatic and terrestrial ecosystems on temporal and spatial scales.
The overall research question raised within this thesis is: How can we assess the internal and external factors of lake development and, therefore, improve the understanding of natural and anthropogenic impacts on lake ecosystems? To examine the development of lakes over time and across different spatial scales, a comprehensive multi-proxy approach was applied, investigating both past and present environmental conditions. The investigation of temporal changes included the analysis of lake sediment cores, using amplicon sequencing (metabarcoding) with targeted primers to recover sedimentary ancient DNA of diatoms and plants. This approach was complemented with microscopic analyses of diatom valves, pollen, and charcoal particles, as well as biogeochemical analyses, including organic carbon, nitrogen, and XRF-derived elemental measurements. The assessment of the modern lake condition focused on the impact of the climate, permafrost, and catchment land cover on the lake water hydrochemical and isotopic conditions, macrophyte diversity, and recent sedimentary DNA from surface sediments.
The cumulative thesis consists of an introduction, four manuscripts and a synthesis. The main findings of this thesis were provided by data gained from the outlined multi-proxy approach, and presented in separate manuscripts that enabled tracing the past long-term development of two lakes since the Late Glacial and Early Holocene, and an assessment of the modern state of 66 lake ecosystems in Yakutia.
Manuscript 1 details the reconstruction of thermokarst lake development of Lake Satagay since the Early Holocene. Using the described methods, it allows to reconstruct lake development stages throughout past millennia. The research findings provide insights into a prolonged shallowing stage, proposed as a potential new stage for conceptual thermokarst lake development. Manuscript 2 explores the environmental evolution around Lake Satagay since the Early Holocene, focusing on past relationships of wildfires and terrestrial plant composition. Open woodland vegetation is found to be more susceptible to wildfires during the Early Holocene, whereas fire occurrence decreased following the establishment of modern larch forest in the region at ca. 4.5 cal ka BP. Manuscript 3 examines major periods of past climatic warming and cooling at Lake Khamra, analyzing both aquatic and terrestrial ecosystems from a relatively stable, non-thermokarst mountain lake. The findings show that climatic trends influenced the vegetation composition, which in turn also impacted the lake ecology. This highlights the necessity for combined aquatic and terrestrial ecosystem studies. Finally, Manuscript 4 assesses the modern state of 66 thermokarst and mountain lakes. The study reveals diverse hydrochemical profiles, which are linked to the physical and morphological states and development stages of the lakes, and reflect both internal and external factors of lake development. These variations correlate with changes in aquatic and terrestrial vegetation, land cover, and land use, illustrating the lakes' complex interactions with environmental factors.
Alaas lakes are an important physical and cultural resource of Yakutia and are presently used in the daily lives of local people. Investigating both paleolimnological changes and modern conditions improves the understanding of the lake ecology in the unique permafrost zone of eastern Siberia. Findings highlight alaas lakes, directly connected to permafrost, as climate sensitive landforms, that are additionally affected by changes in vegetation, land use, and disturbances such as wildfires. They also suggest the potential inclusion of a stabilized shallowing stage, just before final alaas formation, to the conceptual alaas formation scheme.
Wildfires constitute a key ecological disturbance in the world’s boreal forests. Driven by conditions of the atmosphere and vegetation, wildfires are also inherently connected to recent global change. Unusually intense fire seasons in Siberia, Canada, or Alaska in recent years are making headlines around the world. With their location in the high latitudes, boreal forests experience above-average climatic warming, and continued climate change is expected to further intensify boreal fire regimes. Remote sensing data and paleo-ecological methods are commonly used to evaluate relationships between fire regimes, climate, vegetation, and human activity, on various temporal and spatial scales. However, satellite data remains limited to only few decades of observations, preventing a direct assessment of long-term wildfire dynamics. Studies utilizing paleo-ecological approaches, on the other hand, including the well-established analysis of charcoal particles in lake sediments as an indicator of past wildfires, remain scarce in Siberia. Compared to other regions of the boreal zone, wildfire activity in boreal Siberia and its drivers and impacts remain poorly understood, especially on long timescales. Eastern Siberia is particularly under-represented in the global distribution of paleo-ecological reconstructions of long-term wildfire activity. Despite the high ecological significance of eastern Siberia’s unique deciduous larch forests, growing on deep permafrost in one of the coldest regions on Earth, this pronounced lack of data means that little is known about past trends of wildfire activity or long-term relationships of fire to its environment and human livelihoods.
This thesis uncovers long-term fire regime changes in the Republic of Sakha (Yakutia), eastern Siberia, throughout the past c. 20,000 years by applying a combination of paleo-ecological and modeling approaches. Eleven new records of wildfire activity throughout the Holocene are obtained, based on macroscopic charcoal particles in lake sediments from south-west Yakutia, Central Yakutia, the southern Verkhoyansk Mountains, and the Oymyakon Highlands. The new data, covering periods of the last c. 700 to 10,800 years, enable the creation of the first composite of Holocene charcoal accumulation for the region, representing trends of biomass burning. A high-resolution record of wildfire activity for the first time allows for a determination of fire return intervals throughout the past two millennia. Reconstructed wildfire activity is compared to reconstructions of past vegetation cover and human land use from palynological analyses and sedimentary ancient DNA, as well as climate data. The paleo-ecological approach is complemented by simulations in the individual-based, spatially explicit forest model LAVESI (Larix Vegetation Simulator). The model is expanded by a new fire module and applied to simulate long-term impacts of climate-driven fire regime changes on fine-scale forest dynamics since the Last Glacial Maximum. Findings show that open woodlands and a warm climate coincided with severe wildfires in the Early Holocene, c. 10,000 years ago, from which a potential positive feedback between thinning forests and intensifying wildfires is inferred. Simulations suggest medium-intensity wildfires at return intervals of 50 years or more are benefitting the dominance of fire-resisting larches, whereas stand-replacing fires facilitate the establishment of evergreen conifers. Over the last two millennia, the role of climatic trends was increasingly overruled by human interference as key driver of fire regime changes. A combination of both paleo-ecological and modeling approaches enables a preliminary identification of indigenous land use 800 years ago and its ability to decrease wildfire severity around settlements. Considering that many indigenous land use practices today are less often conducted, or, in the case of the traditional, controlled use of fire in the landscape, were prohibited, these findings have implications for present-day policies in a region where fire regimes are expected to continue intensifying. This thesis for the first time uncovers regional wildfire activity in Yakutia throughout the Holocene by applying a novel combination of paleo-ecological and modeling approaches, unravelling natural and human drivers, and discussing findings and their implications for present and future wildfire activity in a unique region already faced with rapid environmental changes.
Only a few palaeo-records extend beyond the Holocene in Yakutia, eastern Siberia, since most of the lakes in the region are of Holocene thermokarst origin. Thus, we have a poor understanding of the long-term interactions between terrestrial and aquatic ecosystems and their response to climate change. The Lake Khamra region in southwestern Yakutia is of particular interest because it is in the transition zones from discontinuous to sporadic permafrost and from summergreen to evergreen boreal forests. Our multiproxy study of Lake Khamra sediments reaching back to the Last Glacial Maximum 21 cal ka BP, includes analyses of organic carbon, nitrogen, XRF-derived elements, sedimentary ancient DNA amplicon sequencing of aquatic and terrestrial plants and diatoms, as well as classical counting of pollen and non-pollen palynomorphs (NPP). The palaeogenetic approach revealed 45 diatom, 191 terrestrial plant, and 65 aquatic macrophyte taxa. Pollen analyses identified 34 pollen taxa and 28 NPP taxa. The inferred terrestrial ecosystem of the Last Glacial comprises tundra vegetation dominated by forbs and grasses, likely inhabited by megaherbivores. By 18.4 cal ka BP a lake had developed with a high abundance of macrophytes and dominant fragilarioid diatoms, while shrubs expanded around the lake. In the Bølling-Allerød at 14.7 cal ka BP both the terrestrial and aquatic systems reflect climate amelioration, alongside lake water-level rise and woodland establishment, which was curbed by the Younger Dryas cooling. In the Early Holocene warmer and wetter climate led to taiga development and lake water-level rise, reflected by diatom composition turnover from only epiphytic to planktonic diatoms. In the Mid-Holocene the lake water level decreased at ca. 8.2 cal ka BP and increased again at ca. 6.5 cal ka BP. At the same time mixed evergreen-summergreen forest expanded. In the Late Holocene, at ca. 4 cal ka BP, vegetation cover similar to modern conditions established. This study reveals the long-term shifts in aquatic and terrestrial ecosystems and a comprehensive understanding of lake development and catchment history of the Lake Khamra region.
