Sediment records of two Italian subalpine lakes (Lake Garda and Lake Ledro) were analyzed in order to reconstruct their ecological evolution over the past several hundred years. A multi-proxy and multi-site approach was applied in order to disentangle the effects of local anthropogenic forcings, such as nutrients, and climate impacts on the two lakes and their catchments. Biological indicators (sub-fossil pigments, diatoms and Cladocera) were used to reconstruct changes in the aquatic food web and to define the lake reference conditions, while geochemical methods, i.e. wavelength-dispersive X-ray fluorescence spectroscopy (WD-XRF), were used to provide quantitative information on the different physical or chemical processes affecting both lake and catchment systems. Sub-fossil pigments and diatoms, together with their respective inferred TP values, suggested very stable oligotrophic conditions in both lakes until the 1960s. The period following was affected by nutrient enrichment, which led to a drastic shift in the phytoplanktonic community. The response of sub-fossil pigments and diatoms to major climatic anomalies such as the Medieval Climatic Anomaly (MCA) and the Little Ice Age (LIA) were not pronounced, and the taxonomic composition remained relatively stable. On the contrary, these proxies showed an indirect response to climate variability since the beginning of the nutrient enrichment phase in the 1960s. In Lake Garda, the winter temperature regulates the water column mixing, which in its turn controls the degree of nutrient fertilization of the entire water column, and the related phytoplankton growth. In Lake Ledro a rapid reorganization of planktonic diatoms was observed only during the temperature recovery after the LIA, while recent temperature effects are masked by the prevailing nutrient effects. In Lake Garda, Cladocera remains responded in quantitative and qualitative terms to climatic changes, whereas in Lake Ledro they appeared to be mainly affected by variations in hydrological regimes, i.e. flood events. Cladocera remains corroborated the nutrient enrichment after the 1960s in both lakes as inferred by diatoms and pigments. In Lake Garda, the geochemical data showed a pronounced shift in elemental composition since the mid-1900s, when major elements and lithogenic tracers started to decrease, while some elements related to redox conditions and other (contaminant) trace elements increased. The general trends since the mid-1900s agree with the biological records. However, some differences recorded in the two different basins of Lake Garda reflected the effects of local conditions, both related to hydrology and sedimentation patterns. Lake Ledro showed higher short-term variability for most elements, even though some features were comparable to Lake Garda. The geochemical record of Lake Ledro revealed a major influence of human-induced lake-level fluctuations and catchment properties. This paleolimnological study allows us to place temporally restricted limnological surveys into a longer-term secular perspective, which is highly valuable for the definition of lake reference conditions. Because the restoration targets are usually based on the lake reference conditions, this study highlighted also the necessity to pay particular attention to the lake-specific sensitivity patterns. The multi-proxy and multi-site approach showed that the lake conditions of large and deep lakes in northern Italy, such as Lake Garda, are mainly driven by nutrient enrichment and/or climate change. In contrast, smaller lakes with larger catchment areas, such as Lake Ledro, are seemingly more impacted by conditions and processes occurring in the drainage basin.

Natural archives such as lake sediments allow us to assess contemporary ecosystem responses to climate and environmental changes in a long-term context beyond the few decades to at most few centuries covered by monitoring or historical data. To achieve a comprehensive view of the changes preserved in sediment records, multi-proxy studies – ideally in high resolution – are necessary. However, this combination of including a range of analyses and high resolution constrains the amount of material available for analyses and increases the analytical costs. Infrared spectroscopic methods are a cost-efficient alternative to conventional methods because they offer a) a simple sample pre-treatment, b) a rapid measurement time, c) the non- or minimal consumption of sample material, and d) the potential to extract quantitative and qualitative information about organic and inorganic sediment components from a single measurement. The main objective of this doctoral thesis was twofold. The first part was to further explore the potential of Fourier transform infrared (FTIR) and visible-near infrared (VNIR) spectroscopy in paleolimnological studies as a) an alternative tool to conventional methods for quantifying biogenic silica (bSi) – a common proxy of paleoproductivity in lakes – in sediments and b) as a tool to infer past lake-water total organic carbon (TOC) levels from sediments. In a methodological study, I developed an independent application of FTIR spectroscopy and PLS modeling for determining bSi in sediments by using synthetic sediment mixtures with known bSi content. In contrast to previous models, this model is independent from conventional wet-chemical techniques, which had thus far been used as the calibration reference, and their inherent measurement uncertainties. The second part of the research was to apply these techniques as part of three multi-proxy studies aiming to a) improve our understanding of long-term element cycling in boreal and arctic landscapes in response to climatic and environmental changes, and b) to assess ongoing changes, particularly in lake-water TOC, on a centennial to millennial time scale. In the first applied study, high-resolution FTIR measurements of the 318-m long sediment record of Lake El’gygytgyn provided a detailed insight into long-term climate variability in the Siberian Arctic over the past 3.6 million years. Highest bSi accumulation occurred during the warm middle Pliocene (3.6-3.3 Ma), followed by a gradual but variable decline, which reflects the first onset of glacial periods and then the finally full establishment of glacial–interglacial cycles during the Quaternary. The second applied study investigated the sediment record of Torneträsk in subarctic northern Sweden also in relation to climate change, but only over the recent post-glacial period (~10 ka). By comparing responses to past climatic and environmental forcings that were recorded in this large-lake system with those recorded in small lakes from its catchment, I determined the significance and magnitude of larger-scale changes across the study region. Three different types of response were identified over the Holocene: i) a gradual response to the early landscape development following deglaciation (~10000-5300 cal yr BP); ii) an abrupt but delayed response following climate cooling during the late Holocene, which occurred c. 1300 cal yr BP – about 1000-2000 years later than in smaller lakes from the area; and iii) an immediate response to the ongoing climate change during the past century. The rapid, recent response in a previously rather insensitive lake-ecosystem emphasizes the unprecedented scale of ongoing climate change in northern Fennoscandia. In the third applied study, VNIR-inferred lake-water TOC concentrations from lakes across central Sweden showed that the ongoing, observed increase in surface water TOC in this region was in fact preceded by a long-term decline beginning already AD 1450-1600. These dynamics coincided with early human land use activities in the form of widespread summer forest grazing and farming that ceased over the past century. The results of this study show the strong impact of past human activities on past as well as ongoing TOC levels in surface waters, which has thus far been underestimated. The research in this thesis demonstrates that infrared spectroscopic methods can be an essential component in high-resolution, multi-proxy studies of past environmental and climate changes.

Made available in DSpace on 2017-07-10T14:38:17Z (GMT). No. of bitstreams: 1 Marcelo.pdf: 2394563 bytes, checksum: 31237f2a32525b07bfe3366d157e642b (MD5) Previous issue date: 2013-02-19 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Objective: Investigate the temporal evolution of the supply of trace elements, identifying trends in the historical concentration of the drainage basin of the Upper Paraná River Floodplain. Material and Methods: The corers extracted of the Patos Pond and the Garças Pond were sliced into uniform intervals of 2.2 and 2.0 cm respectively. Later the geochronological analysis was performed by the method radiochemical of isotope 210Pb. The quantification of element Mercury was performed with the equipment LUMEX. While the others trace elements were quantified by flame atomic absorption spectrometry, opening following the Method USEPA 3050B. Results: The sedimentation rate of the Garças Pond is 7.7 mm year-1 (2.66 kg m-2 year-1) and of the Patos Pond is 6.0 mm year-1 (1.94 kg m-2 year-1). Conclusion: The sediments of the Patos Pond and the Garças Pond have concentrations of trace elements similar to the background. The main factor that regulates the supply of trace elements in the Upper Paraná River Floodplain is the flood pulses, which can be magnified by the El Niño phenomenon. The burning of cane sugar, increased agriculture, urbanization and release of effluents from steel mills contributed to the increase in the concentration of some trace elements. While the adsorption by macrophytes and process oligotrophication caused by damss upstream of the floodplain, resulted in the reduction of the concentration of other elements / Objetivo: Investigar a evolução temporal do fornecimento de elementos-traço, identificando tendências na concentração histórica da bacia de drenagem da Planície Aluvial do Alto Rio Paraná. Material e Método: Os corers extraídos da Lagoa dos Patos e na Lagoa das Garças foram fatiados em intervalos uniformes de 2,2 e 2,0 cm respectivamente. Posteriormente foi realizada a análise geocronológica pelo método radioquímico do isótopo 210Pb. A quantificação do elemento Mercúrio foi realizada com o equipamento LUMEX. Enquanto os demais elementos-traço foram quantificados por meio de absorção atômica de chama, com abertura seguindo o método USEPA 3050B. Resultados: A taxa de sedimentação da Lagoa das Garças é de 7,7 mm ano-1 (2,66 kg m-2 ano-1) e da Lagoa dos Patos é de 6,0 mm ano-1 (1,94 kg m-2 ano-1). Conclusão: Os sedimentos das Lagoas dos Patos e da Lagoa das Garças possuem concentrações de elementos-traço semelhantes aos valores de referência. O principal fator que regula o fornecimento de elementos-traço na planície aluvial do Alto Rio Paraná são os pulsos de inundação, que podem ser magnificados pelo fenômeno climático El Niño. A queima da cana-de-açúcar, aumento da agropecuária, urbanização e lançamento de efluentes de siderúrgicas contribuíram para o aumento da concentração de alguns elementos-traço. Enquanto a adsorção por macrofitas aquáticas e o processo de oligotrofização, causado pelas barragens a montante da planície aluvial, acarretaram na redução da concentração de outros elementos

<p>The objective of the thesis was to explore the potential of diatoms (<i>Bacillariophyceae</i>) as indicators of Holocene climate and environmental change in northern Sweden (Abisko region, 68°21'N, 18°49'E). A modern surface-sediment calibration set including 100 lakes was developed and lake-water pH, sedimentary organic content (assessed by loss-on-ignition) and temperature were identified as most powerful environmental variables explaining the variance within the diatom assemblages. Transfer functions based on unimodal species response models (WA-PLS) were developed for lake-water pH and mean July air temperature (July T), yielding coefficients of determination of 0.77 and 0.70, and prediction errors based on leave-one-out cross-validation of 0.19 pH units and 0.96 °C for lake-water pH and July T, respectively. The transfer functions were validated with monitoring data covering two open-water seasons (lake-water pH) and meteorological records covering the 20th century (July T). The good agreement between diatom-based inferences and measured monitoring data confirmed the prediction ability of the developed transfer functions. </p><p>Analysing a Holocene sediment core from a lake nearby Abisko (Vuoskkujávri), diatoms infer a linearly decreasing July T trend (1.5 °C) since 6,000 cal. BP, which compares well with inferences based on chironomids and pollen from the same sediment core. The lake-water pH inference shows a pattern of moderate natural acidification (c. 0.5 pH units) since the early Holocene, reaching present-day pH values at c. 5,000 cal. BP. By fitting fossil diatom samples to the modern calibration set by means of residual distance assessment within canonical correspondence analysis (CCA), the early Holocene (between 10,600 and 6,000 cal. BP) was identified as a problematic time-period for diatom-based inferences and, consequently, reconstructions during this period are tentative. Pollen-based inferences also show 'poor' fit between 10,600 and 7,500 cal. BP and chironomids probably provide the most reliable July T reconstruction at Vuoskkujávri, with 'poor' fit only during the initial part of the Holocene (between 10,600 and 10,250 cal. BP). </p><p>Possible factors confounding diatom-based July T inferences were investigated. Using detrended CCA (DCCA), Holocene sediment sequences from five lakes indicate that during the early Holocene, mainly physical factors such as high minerogenic erosion rates, high temperature and low light availability may have regulated diatom assemblages, favouring <i>Fragilaria</i> species. In all five lakes, diatom assemblages developed in a directional manner, but timing and scale of development differed substantially between lakes. The differences are attributed primarily to the geological properties of the lake catchments (with strong effects on lake-water pH), but other factors such as climatic change, vegetation, hydrologic setting and in-lake processes appear to regulate diatom communities in each lake differently. The influence of long-term natural acidification on diatom assemblages progressively declined during the Holocene with corresponding increase of the influence of climatic factors.</p>

The objective of the thesis was to explore the potential of diatoms (Bacillariophyceae) as indicators of Holocene climate and environmental change in northern Sweden (Abisko region, 68°21'N, 18°49'E). A modern surface-sediment calibration set including 100 lakes was developed and lake-water pH, sedimentary organic content (assessed by loss-on-ignition) and temperature were identified as most powerful environmental variables explaining the variance within the diatom assemblages. Transfer functions based on unimodal species response models (WA-PLS) were developed for lake-water pH and mean July air temperature (July T), yielding coefficients of determination of 0.77 and 0.70, and prediction errors based on leave-one-out cross-validation of 0.19 pH units and 0.96 °C for lake-water pH and July T, respectively. The transfer functions were validated with monitoring data covering two open-water seasons (lake-water pH) and meteorological records covering the 20th century (July T). The good agreement between diatom-based inferences and measured monitoring data confirmed the prediction ability of the developed transfer functions. Analysing a Holocene sediment core from a lake nearby Abisko (Vuoskkujávri), diatoms infer a linearly decreasing July T trend (1.5 °C) since 6,000 cal. BP, which compares well with inferences based on chironomids and pollen from the same sediment core. The lake-water pH inference shows a pattern of moderate natural acidification (c. 0.5 pH units) since the early Holocene, reaching present-day pH values at c. 5,000 cal. BP. By fitting fossil diatom samples to the modern calibration set by means of residual distance assessment within canonical correspondence analysis (CCA), the early Holocene (between 10,600 and 6,000 cal. BP) was identified as a problematic time-period for diatom-based inferences and, consequently, reconstructions during this period are tentative. Pollen-based inferences also show 'poor' fit between 10,600 and 7,500 cal. BP and chironomids probably provide the most reliable July T reconstruction at Vuoskkujávri, with 'poor' fit only during the initial part of the Holocene (between 10,600 and 10,250 cal. BP). Possible factors confounding diatom-based July T inferences were investigated. Using detrended CCA (DCCA), Holocene sediment sequences from five lakes indicate that during the early Holocene, mainly physical factors such as high minerogenic erosion rates, high temperature and low light availability may have regulated diatom assemblages, favouring Fragilaria species. In all five lakes, diatom assemblages developed in a directional manner, but timing and scale of development differed substantially between lakes. The differences are attributed primarily to the geological properties of the lake catchments (with strong effects on lake-water pH), but other factors such as climatic change, vegetation, hydrologic setting and in-lake processes appear to regulate diatom communities in each lake differently. The influence of long-term natural acidification on diatom assemblages progressively declined during the Holocene with corresponding increase of the influence of climatic factors.

L’eutrophisation et le réchauffement climatique sont reconnus comme des forçages majeurs du fonctionnement des lacs. Toutefois les connaissances concernant la réponse des communautés microbiennes eucaryotes à ces forçages sont encore très lacunaires, alors même que les microbes eucaryotes, porteurs d’une vaste diversité taxonomique et fonctionnelle, sont des acteurs clés des réseaux trophiques lacustres. La pertinence des approches paléolimnologiques pour comprendre les impacts de ces forçages sur les communautés lacustres n’est plus à démontrer, mais aujourd’hui l’intégration des outils moléculaires pour analyser l’ADN archivé dans les sédiments offre des opportunités nouvelles pour reconstituer la dynamique passée de la biodiversité lacustre. Dans ce cadre, en s’appuyant sur le couplage entre paléolimnologie et outils de séquençage massif appliqués à l’ADN sédimentaire, ces travaux ont pour but (i) d’apporter des connaissances concernant la préservation de l’ADN des microbes eucaryotes dans les sédiments lacustres (ii) d’appliquer l’approche de paléogénétique sur des carottes sédimentaires issues de 3 lacs pour révéler la dynamique à long terme (de la décennie au millénaire) des microbes eucaryotes en lien avec l’évolution des conditions climatiques et anthropiques. Les résultats acquis sur le lac du Bourget ont permis de mettre en évidence l’efficacité d’archivage de l’ADN planctonique dans les sédiments récents pour la plupart des groupes eucaryotes (notamment chrysophycées, chytrides, chlorophytes, cercozoaires, ciliés, dinophycées). A partir d’une collection de carottes (issues du lac suédois Nylandssjön), l’effet de la diagénèse s’opérant au cours des premières années d’enfouissement a été évalué, permettant de démontrer que si la richesse taxonomique n’est pas impactée, des variations peuvent être détectées dans la structure de la communauté au cours des 10 premières années d’archivage avec une stabilisation du signal au-delà de cette période. L’approche paléogénétique a, en parallèle, été déployée d’une part à l’échelle du siècle sur deux lacs de même typologie mais ayant subi des niveaux d’eutrophisation contrastés, et d’autre part à une échelle temporelle plus longue (2200 ans) pour deux lacs de typologie contrastée (lac du Bourget, France et Igaliku, Groenland). Les résultats acquis démontrent que des réarrangements des communautés s’opèrent de manière concomitante aux périodes climatiques (réchauffement médiéval, petit âge glaciaire, réchauffement récent), et que le réchauffement climatique au cours des 30 dernières années a plus particulièrement favorisé certains groupes, notamment la richesse et l’abondance des dinophycées (en condition non eutrophe ; lac d’Annecy et du Bourget). Toutefois l’effet de l’eutrophisation est identifié comme le facteur le plus structurant, notamment dans le lac du Bourget (cas d’eutrophisation marquée, ~120 µgP.L-1). La forte influence du niveau d’eutrophisation est détectée sur la communauté eucaryote totale et plus particulièrement sur des groupes spécifiques tels que les chlorophytes et les ciliés. Les réarrangements majeurs de la communauté sont par ailleurs marqués par la mobilisation de taxons rares dans l’assemblage microbien eucaryote suggérant le rôle de la biosphère rare dans la capacité tampon des écosystèmes. Ces travaux pluridisciplinaires comptent parmi les premières études paléogénétiques appliquées aux microbes eucaryotes lacustres, contribuant de manière inédite aux connaissances de leur dynamique temporelle à long terme. Ces études tendent à confirmer le potentiel de ces approches pour reconstituer une vaste diversité de communautés lacustres. Les perspectives qui se dessinent dans la continuité de ces travaux concernent à la fois des aspects méthodologiques autour de la calibration du signal ADN archivé et la nécessité de déployer cette approche pour des lacs (sélectionnés) de typologies et histoires écologiques variées. / Eutrophication and climate warming are key factors governing lake functioning. However, there is a lack of knowledge about the response of microbial eukaryotic communities to these forcing factors even though microbial eukaryotes represent a huge taxonomic and functional diversity within lacustrine trophic networks. Paleolimnology has a well-established reputation for providing valuable insights into the drivers of biological assemblages over long time scales. The emergence of DNA analyses of lake sediments opens up many new opportunities for the reconstruction of past lacustrine biodiversity, including taxa that do not leave distinct morphological fossils. The present work aimed (i) to gain knowledge about the preservation of microbial eukaryotes DNA in lacustrine sediments (ii) to apply DNA-based methods to dated sediments in order to reveal the long-term dynamics (centennial to millennial) of microbial eukaryotes related to climatic and anthropogenic changes. The results obtained for Lake Bourget demonstrated the good efficiency of planktonic DNA archiving in recent sediments for most of microbial groups (chrysophyceae, chytrids, chlorophytes, cercozoa, ciliates, dinophyceae …). In complement, the use of a unique collection of freeze cores of varved sediment (Lake Nylandssjön, Sweden) allowed to assess the effects of diagenetic processes on microbial eukaryotes DNA occurring during the first years of burying. While the richness of the microbial eukaryotic community was not impacted, modifications were detected on the community structure during the first 15 years after deposition, then the DNA signal became stable. The paleoecological approach was applied to quantify centennial to millennial-scale dynamics on two deep peri-alpine lakes selected for their contrasted trophic history (lakes Bourget and Annecy, France) and two lakes with contrasted typologies (Lake Bourget, France and Lake Igaliku, Greenland). The results showed that some community rearrangements were concomitant with climate events (i.e. medieval warming, little ice age, recent warming) and that the recent climatic warming (over the last 30 years) favored more particularly some microbial groups including the dinophyceae (in terms of richness and relative abundance, in lakes Annecy and Bourget). However, the eutrophication seemed to prevail as a driver of these biological assemblages, in particular for Lake Bourget submitted to a marked eutrophication (up to 120 µg P. L-1 in the 1970s). The strong impact of the eutrophication was detected both at the whole community level and for specific groups such as chlorophytes and ciliates. Major rearrangements within eukaryotes community were also marked by the mobilization of rare taxa suggesting an important role of the rare biosphere as a reservoir of diversity to buffer the impacts of environmental stress. This multidisciplinary work thus provide new insights into the long-term dynamics of microbial eukaryotes communities. Our results confirm the potential of the application of high-throughput sequencing to sedimentary DNA for the lacustrine biodiversity reconstruction. Although these approaches are promising for further revolutionizing our understanding of long-term ecological dynamics, careful calibration studies are still to be conducted, as with any paleolimnological proxy. The generalization of our results is also to be tested using a sufficient number of lakes selected for their specific typologies and ecological histories (multi-lakes approach).

The Fairy shrimp Branchinecta gaini Daday, 1910 is the largest freshwater invertebrate in Antarctica and the top-level consumer of local freshwater food webs. Ecological demands of B. gaini that are accompanied by 'ruderal' life strategy together with its spatial distribution that exceeds to Patagonia indicate that it had survived last glacial period in South America and expanded to Antarctica shortly after this epoch endeed. On James Ross Island that is the most extreme environment where B. gaini occurs today was this fairy shrimp considered extinct until year 2008. Its disappearance was based on paleolimnological analysis of several lake sediment cores according to which it inhabited this island between years 4200 to approximately 1500 before present when it died out because of changes in lake catchments caused by harsh neoglacial conditions. Paleolimnological analysis of Monolith Lake presented in this study has shown that this assumption was wrong and B. gaini has lived on James Ross Island throughout neoglacial period up to recent time. Phylogeographic analysis of 16S rDNA of specimens from Patagonia, South Orkneys, South Shetlands and James Ross Island revealed that its high morphological diversity is not supported by this gene and that all examined populations of B. gaini is one species with very few...

Cyanobacterial blooms and their toxins are a major water quality and potential health risk around the world. This thesis developed an analytical method for microcystin congeners in sediments in order to examine their fate in lakes and establish the history of toxin-producing cyanobacteria in relation to environmental change using lake sediments. A novel method for both intra- and extracellular microcystins in lake sediments was developed, consisting of accelerated solvent extraction, hydrophilic-lipophilic balance solid phase extraction and multiple reaction monitoring-based HPLC-MS/MS quantitation. The method achieved comparable recoveries of intra- and extracellular cyanotoxins based on nine microcystins and nodularin (marine analogue). The analytical method was validated using surficial and deeper sediments from seven lakes of diverse geography and trophic state. To study the fate of microcystins, a multi-year, whole lake study of Microcystis blooms was conducted to obtain both in situ and in vitro half-life estimates of microcystin-LA (MC-LA), an understudied, but increasingly reported microcystin. MC-LA appeared to undergo slower rates of decomposition and persist longer than the more frequently studied MC-LR. Experimentally, high light intensity increased in vitro decomposition of dissolved MC-LA while high temperature enhanced decomposition in the particulate phase. Sediment deposition measurements and estimates of sediment-pore water distribution coefficients, sediment accumulation rates, and diffusive fluxes indicated that microcystin congeners differ in their fate. Notably, MC-LA preferentially distributed into pore water and remobilized (by diffusion) from sediments and into overlying water while MC-RR adsorbed more strongly to sediment particles. Finally, the sediment record of an eutrophic lake of major recreational importance was examined to identify possible drivers of toxigenic cyanobacteria and determine if the perceived increase in toxigenic cyanobacteria could be corroborated. Microcystins were detected to the bottom of the core (early 1800s), indicating that toxigenic cyanobacteria were present prior to the first permanent settlements. Microcystins were significantly correlated with changes in diatom-inferred nutrients (DI-TP and DI-TKN) within the sediment core as well as with specific algal pigments. Sediment microcystins in the upper layers also significantly correlated with a 20-year monitoring record for water column microcystins suggesting that sediment microcystins can be used as a proxy for past surface water conditions.

Diatom analysis of basal part of profile PK-1-L contributes to multi-proxy research of former Lake Komořany. At this part of profile radiocarbon dating (dates sediments into Late Glacial and Early Holocene) and LOI (loss on ignition) had been conducted before, of which results have been utilized to more accurate interpretation of diatom analysis conclusions. Apart from diatom valves, presence of stomatocysts of Chrysophyceae has been observed. Having separated diatom valves from 32 sediment samples in intervals 0,4-0,6 cm, permanent preparates have been created. Concentration of valves in a gramme of dry sediment and relative abundance of diatom taxons in each sample have been investigated using light microscopy. In a half of samples subdominants and rare taxons have been observed separately to eliminate the interference from dominant taxons. Cluster analysis based on relative abundances of diatom taxons have been calculated and on its results have been subsequently determined three diatom accumulation zones (DAZ). Moreover trophic and saprobic indices have been calculated and levels of pH, conductivity and concentration of total phosphorus (TP) have been estimated by transfer functions. Even before beginning of Holocene the major shift in composition of diatom communities have happened, to the...

The aims of the thesis were to document the history of the Cladocera (Crustacea) community structure in the Starolesnianske Lake (the High Tatra Mountains, Slovakia) with regards to environmental changes (e. g., Medieval Warm Period, Little Ice Age, anthropogenic acidification, recovery from acidification), and to analyze in detail the development of zooplankton (Cladocera, Copepoda, Rotifera) during the peaking acidification and recovery from acidification (1978 - 2015). Based on results of both the approaches, the appropriateness of using historical data on zooplankton in Tatra lakes between 1909 - 1913 (Minkiewicz, 1914) as a reference condition for the evaluating biological recovery from acidification should have been assessed. The methods used were paleolimnological analyses of lake sediment (namely subfossil Cladocera), analysis of recent zooplankton, and analyses of lake water chemistry. It was found that in the historical record, relative abundances of Cladocera species significantly changed cca 150 years ago (at the end of the Little Ice Age and, in the main, in the period of anthropogenic acidification). The lake, though, has had a very stable species composition of Cladocera during the last cca 2,000 years, represented by four species: Alona quadrangularis, Alonella excisa, Ceriodaphnia...