Limnological assessment of 51 climate-sensitive permafrost-thaw lakes in Central Yakutia, Siberia

Climate is rapidly changing in northern regions, including Central Yakutia, a densely populated area in Siberia. Here, permafrost-thaw lakes in topographical depressions, named “alaas”, are widely distributed. Alaases and the residual lakes within became the traditional home to the indigenous Sakha people, providing critical ecosystem services like fresh water supply, meadows for cattle breeding, or fishing and hunting grounds. Alaas formation is closely related to the Late Glacial and Early Holocene warming, as it was caused by the degradation of permafrost. This makes alaases, and permafrost-thaw lakes in general, highly sensitive to both climatic changes and land use impacts. Global warming is predicted to cause permafrost loss, potentially resulting in new alaas formations and irreversibly changing water quality and biodiversity within the existing alaas lakes. The exact consequences of anthropogenic climate change and land use on these unique landforms are still poorly understood, which may also be a result of lacking data availability. Here, we present a comprehensive new dataset of limnological characteristics of 66 lakes across Central Yakutia Lowland and the Oymyakon Highlands, with a focus on 51 alaas lakes in Central Yakutia. During field work in summer of 2021, we measured lake physical properties (lake depth, pH, specific conductivity) and afterwards we analyzed lake water hydrochemistry including ions, dissolved organic carbon (DOC), isotopic composition (δ18O H20, δD H20), and aquatic and terrestrial plant composition via surface sediment environmental DNA metabarcoding. The majority of alaas lakes are classified as magnesium-bicarbonate types. Isotope concentrations indicate that lakes in the Central Yakutian Lowlands are controlled mainly by evaporation, underlining their sensitivity to future warming. Aquatic vegetation is dominated by submerged macrophytes, whereas terrestrial vegetation mainly consists of graminoids and forbs. Settlements are mostly situated in connected alaas systems, where flowing water results in lower DOC concentration. This “snapshot” of limnological characteristics can be helpful to assess the most critical factors which may be impacted by land use or respond to future warming.