Browsing by Subject "diatoms"
Now showing items 1-4 of 4
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(2021)The changes in lake diatom assemblages as a response to climate warming over the past three decades were examined in 26 lakes across Northwestern Finnish Lapland using multivariate statistical techniques. The lakes are distributed along a steep climatic and vegetational gradient, covering three distinct vegetation zones spanning boreal coniferous forest, mountain birch woodland, and treeless tundra. Lakes were selected following a study realised by Weckström and Korhola in 2001, who had sampled the same lakes for surface-sediment diatom assemblages, physical, and chemical limnological variables. Climate data from the past 30 years was retrieved, showing a slow and steady yearly increase in temperature, with strong seasonal fluctuation and fall months experiencing the strongest warming. Surface sediment samples were taken from the lakes and their diatom communities analysed. A total of 185 diatom taxa representing 27 genera were recorded. Ordination techniques (DCA, CCA) at the genus and species level were performed to identify the main patterns of variation between diatom data from the original data set and the current study, and their relationship to environmental variables. Strong changes were recorded in four of the lakes with major shifts in dominant diatom species. Moderate changes were recorded in eight lakes, where dominance changes were recorded for a few species while the majority remained unchanged. The remaining 14 lakes did not show noticeable changes over the 30-year period. Changes observed in the studied lakes did not follow a widely observed pattern in northern Hemisphere lakes. The results indicate that while climate change is a driving factor behind changing lake dynamics with increasing temperatures and decreasing lake ice cover duration, it cannot be the only force responsible.
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(2016)For the conservation of biodiversity, it is important to examine the factors that shape species richness in different ecosystems. Global warming is predicted to be most pronounced in arctic-alpine areas and arctic environments, especially in major ecotones, like environments close to the tree lines. Therefore by examining the species richness, distribution and requirements of species living in mountainous areas, it is possible to assess the effects of climate change in different spatial scales. Elevational gradients are suitable for this kind of research, because many ecosystems processes and structure of local communities change along elevational gradients. Studies carried out in elevational gradients can help us to find out the mechanisms that shape local communities. The elevational patterns of species richness of micro-organisms like diatoms have been studied increasingly lately, but the results of the factors shaping species richness along elevational gradient are varied between different studies and groups of micro-organisms. Therefore it is important to learn more about the factors that shape species richness of micro-organisms along elevational gradients. In this thesis’s the elevational patterns of species richness and species evenness were studied in three different mountain streams in northern Norway and Kilpisjärvi (n= 44). The study also examines the effects of altitude to taxonomic relatedness of diatom species. Diatom and water chemistry samples were collected in August 2013. Generalized linear models (GLM) were used to analyse species richness and the correlation between environmental variables and species richness were examined with pairwise correlation tests. Taxonomic distinctness was calculated with taxondive-command. According to the GLM, the species richness was best explained (49,2 %) by pH of stream water, stream depth, conductivity and altitude. Species evenness was best explained (45,6 %) by water temperature and total nitrogen (TN). Altitude showed a statistically significant relation to species richness (p= 0,003) and species evenness only in Lepänjoki (p< 5,45e+07). Species were not phylogenetically more clustered as elevation increased. Altitude did not explain the taxonomic distinctness of diatom species in the research streams. It can be concluded that a deeper riverbed guarantee more stable conditions to diatom species. Similarly, higher water pH value is more favorable habitat for diatoms, than acidic waters. Altitude may affect species richness through bedrock geology, which probably affects pH value and conductivity in the research streams. The short elevational gradients probably affect the fact that species richness did not decrease as altitude increased and that the species were not closely related to each other at the upper end of the gradient.
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(2023)Local climatic interactions between ice, ocean and atmosphere in Northwest Atlantic are significant due to their impacts on global climate. Sea-surface conditions and their links to major climatic patterns during the late-Holocene offshore southeastern Newfoundland, Placentia Bay, were studied using diatoms as paleobioindicators. The record indicates moderate conditions with Arctic influence being little stronger than Atlantic influence during the time period between 5.8 and 4.75 ka BP. The time period between 4.75 and 2 ka BP is dominated by Atlantic influence, except for a cold pulse around 3.5 ka BP. There is a considerable increase in Arctic influence during the time period between 2 and 0.4 ka BP. The strength of the inner Labrador Current seems to be the most important factor affecting the conditions in Placentia Bay. It follows both the NAO index and the strength of AMOC being strongest when the NAO index is positive and AMOC is strong. Cold periods in the record match with positive NAO. Meltwater and sea ice content in the inner Labrador Current seems to be dependent on the conditions in Baffin Bay. The AO index and the orbitally driven HTM, Neoglacial cooling and Roman warm period events affected the dynamics in Baffin Bay during the late-Holocene. Also, the AMOC caused either additional cooling or melting in the region depending on its strength. The major shift at 2 ka BP matched with a recorded shift in the deep convection rate in the Labrador Sea.
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(2023)Local climatic interactions between ice, ocean and atmosphere in Northwest Atlantic are significant due to their impacts on global climate. Sea-surface conditions and their links to major climatic patterns during the late-Holocene offshore southeastern Newfoundland, Placentia Bay, were studied using diatoms as paleobioindicators. The record indicates moderate conditions with Arctic influence being little stronger than Atlantic influence during the time period between 5.8 and 4.75 ka BP. The time period between 4.75 and 2 ka BP is dominated by Atlantic influence, except for a cold pulse around 3.5 ka BP. There is a considerable increase in Arctic influence during the time period between 2 and 0.4 ka BP. The strength of the inner Labrador Current seems to be the most important factor affecting the conditions in Placentia Bay. It follows both the NAO index and the strength of AMOC being strongest when the NAO index is positive and AMOC is strong. Cold periods in the record match with positive NAO. Meltwater and sea ice content in the inner Labrador Current seems to be dependent on the conditions in Baffin Bay. The AO index and the orbitally driven HTM, Neoglacial cooling and Roman warm period events affected the dynamics in Baffin Bay during the late-Holocene. Also, the AMOC caused either additional cooling or melting in the region depending on its strength. The major shift at 2 ka BP matched with a recorded shift in the deep convection rate in the Labrador Sea.
Now showing items 1-4 of 4