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Browsing by Author "Koljonen, Vilma"

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  • Koljonen, Vilma (2024)
    Human-induced climate change is one of the major crises of our time. Benthic and planktonic microalgae are typically the dominant primary producers in arctic lakes with low productivity and low biodiversity. Microalgal species are well adapted to the harsh conditions and large seasonal fluctuations of the arctic environment, but due to climate change-driven changes, the conditions in the Arctic region will change radically, threatening the primary production and biodiversity of the arctic lakes. The topic is important to study, as we still don’t know much about the biodiversity of arctic lakes. This thesis studies the biodiversity of an arctic lake as well as the relationship between primary production, climate fluctuations, and landscape development during the Holocene by using sedimentary pigments from lake Kuutsjärvi. Sedimentary pigments can be used as a biochemical marker for the presence of the lake’s past microalgal populations. A wide range of chlorophylls, carotenoids, and other lipid-soluble pigments are preserved in the lake sediments. Certain accessory pigments can be associated with certain algal groups. Some pigments, on the other hand, are indicators of the overall productivity of the ecosystem. Nine different sedimentary pigments were detected from the samples: β-carotene, Alloxanthin, Diatoxanthin, Echinenone, Myxoxanthophyll, Zeaxanthin, Canthaxanthin, Lutein and a-chlorophyll. In addition to the pigment samples, TOC% and C:N values measured from the sediment describing organic carbon of the catchment area are examined. Results are analyzed with stratigraphy, boxplot graphs, and PCA-analysis. From the results, it can be concluded that the lake’s primary production was at its peak during the Holocene thermal maximum, when especially cyanobacteria were the dominant microalgal group. Temperature conditions are therefore a significant factor controlling arctic lake primary production. The concentration of diatom-derived Diatoxanthin in the sediment varies greatly throughout the Holocene, indicating that diatoms are more controlled by the chemical properties of the lake rather than by temperature conditions. Microalgal primary production is also controlled by nutrients, light availability, and the physical characteristics of the catchment area. Changes in primary production over the Holocene are the key to understanding the ecosystem’s adaptation capacity to changes in climate and environmental conditions. The results show the substantial impact of the Holocene thermal maximum on the lake’s primary production. Based on the results, it can be estimated that human-induced climate change will affect the lake’s microalgal populations significantly. Fundamental changes in primary production may already occur in the near future. Understanding past changes will help us understand potential future changes.