Comment on egusphere-2024-2470

Le résumé fourni par la source

Abstract. Lake ecosystems are affected globally by climate warming and anthropogenic influences. However, impacts on boreal lake ecosystems in Siberia, remain largely underexplored. Our aim is to determine if shifts in diatom assemblages in a remote lake in eastern Siberia are related to climate warming, similar to observations in temperate regions, while also exploring how the ecosystem might be influenced by climate and pollution through various biogeochemical proxies. We analysed continuous sediment samples from a 210Pb–137Cs–dated short core from Lake Khamra (59.99° N, 112.98° E), covering 220 years (ca. 1790–2015 CE), with the specific feature of combining a variety of proxies on the same sample material to provide a comprehensive record of environmental changes in this less–examined region. Biogeochemical proxies include carbon and nitrogen concentrations (TOC, TN) and corresponding stable isotopes of bulk sediment samples (δ13C, δ15N), as well as diatom silicon isotopes (δ30Sidiatom), alongside light microscope diatom species analysis. The diatom assemblage at Lake Khamra is dominated by few planktonic species, primarily Aulacoseira. At 1970 CE, we observe a significant shift in diatom assemblages, with a marked increase in the planktonic species D. stelligera and a decrease in Aulacoseira, which we attribute to recent global warming, earlier ice–out, and potential enhanced summer thermal stratification, aligning with similar changes seen in temperate lake ecosystems. Furthermore, we see evidence for an increased diatom productivity supported by rising diatom valve concentrations and accumulation rates. Carbon and nitrogen levels increase in the 1950s, preceding the 1970 CE shift in diatom assemblages, suggesting that hydroclimatic and fire–related changes in the catchment significantly influence the limnology. Increased precipitation and weathering are discussed to alter silica sources leading to decreasing δ30Sidiatom after 1970 CE and suggest δ30Sidiatom as a proxy for weathering rather than productivity at Lake Khamra. Indications of human impact on the lake ecosystem include a 13C–depletion, linked to fossil fuel combustion since the 1950s, and changes in diatom species composition, such as the increased abundance of planktonic A. formosa. Furthermore, we observe a clear acidification trend since the 1990s, marked by a drastic increase in Mallomonas scales. Strong correlation to mercury accumulation rates, determined in a previous study, indicates a long–distance air pollution trend. We conclude the ecosystem of Lake Khamra is profoundly affected by climate warming and human–induced pollution, emphasising the urgent need for comprehensive research to address and mitigate these impacts on remote lake ecosystems to secure natural water resources.

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