Submitted by Biblioteca de Pós-Graduação em Geoquímica BGQ (bgq@ndc.uff.br) on 2017-11-01T15:59:40Z No. of bitstreams: 1 Dissertação _Anna Beatriz Jones Oaquim_Digital.pdf: 6278668 bytes, checksum: 60236079c59e16ffdb171fe240dd8a21 (MD5) / Made available in DSpace on 2017-11-01T15:59:40Z (GMT). No. of bitstreams: 1 Dissertação _Anna Beatriz Jones Oaquim_Digital.pdf: 6278668 bytes, checksum: 60236079c59e16ffdb171fe240dd8a21 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Fundação de Amparo a Pesquisa do Estado do Rio de Janeiro / Universidade Federal Fluminense. Instituto de Química. Programa de Pós-Graduação em Geoquímica, Niterói, RJ / The use of diatoms as micropaleontological indicators has been used in the last decades, since these organisms that are sensitive to environmental changes, having their frustules preserved in the sediments, allow paleoenvironmental and / or paleoclimatic reconstructions. In this context, the present study aims to reconstruct regional climatic variations in the South Shetland Islands, located on the west coast of the Antarctic Peninsula, using a corer with 50cm sampled at the Glubokoe Deepe Proglacial Lake (62 ° 11,066'S, 58 ° 54,413'O), Fildes Peninsula, King George Island, based on the fossil record of diatoms. In qualitatively analysis on the sedimentary layers from the period 2013 to 1737, 34 taxa were found and identified, of which only 19 were considered as frequent. Among these 19 taxa the most abundant species along all layers was the centric diatom Aulacoseira glubokoyensis, a new species discovered throughout this study, followed by penate diatoms, which present a high diversity. Aulacoseira glubokoyensis showed a decrease in relative abundance and cell size in the period of higher ozone variation, probably associated to the adaptation to this environmental condition associated to the increase of UV-B radiation. Based on the correlations obtained between the environmental variables and the relative abundance of the frequent taxa, it was possible to establish three reconstruction models, one for temperature, the other for the average energy of cyclones occurring between 50 ° and 70 ° S and other for the minimum ozone content in the atmosphere. The first model of reconstruction was based on the relative abundance of Brachysira minor and Pinnularia sp. And presented an associated error of only 13%, the second in the relative abundance of Nitzschia cf. Kleinteichiana, Pinnularia borealis, Gomphonema sp. with an average error of 2% and the last one, of minimum ozone, was based in the relative abundance of Planothidium australe, Pinnularia borealis, Gomphonema sp. and Humidophila tabellariaeformis, with mean associated error of 11%. Thereby, for this region diatom assemblies can be used as paleoclimatic reconstructors / The use of diatoms as micropaleontological indicators has been used in the last decades, since these organisms that are sensitive to environmental changes, having their frustules preserved in the sediments, allow paleoenvironmental and / or paleoclimatic reconstructions. In this context, the present study aims to reconstruct regional climatic variations in the South Shetland Islands, located on the west coast of the Antarctic Peninsula, using a corer with 50cm sampled at the Glubokoe Deepe Proglacial Lake (62 ° 11,066'S, 58 ° 54,413'O), Fildes Peninsula, King George Island, based on the fossil record of diatoms. In qualitatively analysis on the sedimentary layers from the period 2013 to 1737, 34 taxa were found and identified, of which only 19 were considered as frequent. Among these 19 taxa the most abundant species along all layers was the centric diatom Aulacoseira glubokoyensis, a new species discovered throughout this study, followed by penate diatoms, which present a high diversity. Aulacoseira glubokoyensis showed a decrease in relative abundance and cell size in the period of higher ozone variation, probably associated to the adaptation to this environmental condition associated to the increase of UV-B radiation. Based on the correlations obtained between the environmental variables and the relative abundance of the frequent taxa, it was possible to establish three reconstruction models, one for temperature, the other for the average energy of cyclones occurring between 50 ° and 70 ° S and other for the minimum ozone content in the atmosphere. The first model of reconstruction was based on the relative abundance of Brachysira minor and Pinnularia sp. And presented an associated error of only 13%, the second in the relative abundance of Nitzschia cf. Kleinteichiana, Pinnularia borealis, Gomphonema sp. with an average error of 2% and the last one, of minimum ozone, was based in the relative abundance of Planothidium australe, Pinnularia borealis, Gomphonema sp. and Humidophila tabellariaeformis, with mean associated error of 11%. Thereby, for this region diatom assemblies can be used as paleoclimatic reconstructors

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Climate change affects lake ecosystems in many ways by direct and indirect temperature impacts on hydrophysical structure, hydrology, chemical cycles and on biological interactions. The identification of these climate signals can be complicated and superimposed by other environmental changes, such as land use changes. The aim of this thesis was to seperate temperature effects from effects of management and other environmental influences and to understand the underlying complex processes causing significant changes of ecosystem states. This understanding is important for decisions of lake and reservoir managers to counteract unfavorable consequences of climate change. For the recent study, long-term data of meteorological, hydrophysical and biological variables (phytoplankton, crustacean zooplankton, fish) of the German drinking water reservoir Saidenbach were analysed. Based on this long-term data set, strong indicators for climate induced changes have been identified. In particular, increasing water temperatures since 1975, earlier break up of ice covers and an altered hydrophysical structure could be detected. Thereby, stratification stability increased and turbulent mixing decreased in summer. The water of the reservoir warmed more than the tributaries resulting in a trend to deeper entrainment of the inflows. As further indicators of climate change, an increased annual biomass of phytoplankton and species shifts in the phytoplankton community in spring and summer had been observed. During the spring mass development, the diatom Aulacoseira subarctica became dominant in recent years with warm winters and early ice-out. Its unusual spatial pattern with occurrences in aphotic depths could be explained by easier resuspension compared to other diatoms. By being resuspended first and establishing a high inoculum, A. subarctica profits from an earlier ice-out and earlier full circulation. In spite of a reduced nutrient loading to the epilimnion, in summer, the diatom Fragilaria crotonensis was displaced increasingly by cyanobacteria. This species shift could be explained well by the hydrophysical regime shift. Although, the annual total phytoplankton biomass increased since 1990, the crustacean zooplankton in Saidenbach reservoir did not seem to profit from improved food resources. To the contrary, Daphnia abundances reduced tremendously. We could show that the influcence of fish stocks were underestimated. The stocked silvercarp may have contributed up to 70 % of the total zooplanktivorous fish biomass which had a temperature and density dependent effect. The faster growth of Daphnia at higher temperatures could not compensate for the more actively grazing fish when stock of zooplankitvorous fish was too high. Still, temperature was identified as the most important factor that explained 29 % of the zooplankton phenology, while the second most important predictors were zooplanktivorous fish biomass and nutrient loading, explaining 18 % of the variance. The importance of submerged macrophytes in shallow lakes is well investigated. To increase also the understanding of their impact and their role during climate change on water quality in deep lakes, a model for stratified lakes that includes submerged macrophytes was developed. The simulations showed that macrophyte effects were mainly positive for water quality and macrophytes in deep lakes were able to potentially reduce summer phytoplankton, especially cyanobacteria by 50 % in 11 m deep and still by 15 % in 100 m deep oligotrophic lakes. Nutrient competition with phytoplankton contributed most to this macrophyte effect. In conclusion, for deep lake restoration the re-establishment of submerged macrophytes might be as important as for shallow lakes. The full lake model includes hydrophysical and ecological submodules and thus will allow further comprehensive climate simulations and the evaluation of the effectivity of adaptive strategies and scenarios for deep lakes and reservoirs. / Der Klimawandel beeinflusst Seeökosysteme vielfältig durch direkte und indirekte Temperatureffekte auf die hydrophysikalische Struktur, die Hydrologie, chemische Kreisläufe und biologische Interaktionen. Die Identifikation von Klimasignalen kann durch Landnutzungs- und weitere Umweltveränderungen überlagert werden. Ziel dieser Arbeit war es, Temperatureffekte von Effekten zu unterscheiden, die durch Gewässermanagement oder anderen Umweltveränderungen verursacht werden. Weiterhin sollten komplexe Prozesse verstanden werden, die zu signifikanten Veränderungen in Seeökosystemen führen. Dieses Verständnis ist für Talsperren- und Gewässermanager von besonderer Bedeutung, um ungewünschten Folgen des Klimawandels entgegenwirken zu können. Für die Studie wurden Langzeitdaten für meteorologische, hydrophysikalische und biologische Variablen (Phytoplankton, Crustaceen-Zooplankton, Fischbesatz) der Talsperre Saidenbach ausgewertet. Mehrere Indikatoren für die Auswirkungen des Klimawandels konnten basierend auf diesen Daten identifiziert werden. Diese gehören insbesondere eine Erhöhung der Wassertemperatur seit 1975, zeitigere Eisaufbrüche und eine veränderte Schichtungsstruktur. Dabei wurde im Sommer die Schichtungsstabilität höher und die Intensität der Durchmischung geringer. Das Wasser in der Talsperre erwärmte sich stärker als die Zuflüsse, wodurch diese sich zunehmend tiefer und unterhalb der Thermokline einschichten. Eine zunehmende jährliche Phytoplanktonbiomasse und Artenwechsel innerhalb der Planktongemeinschaft sind weitere Indikatoren für Klimafolgen. Die Kieselalge Aulacoseira subarctica erlangte in Jahren mit warmen Wintern und zeitigen Eisaufbrüchen eine Dominanz während der Frühjahrsentwicklung. Das ungewöhnliche Auftreten dieser Art in aphotischen Tiefen konnte durch eine leichtere Resuspension im Vergleich zu anderen Kieselalgen erklärt werden. Durch zeitige Resuspension gleich nach Eisaufbruch kann A. subarctica ein hohes Inokulum etablieren. Trotz reduzierter Nährstoffzufuhr ins Epilimnion wurde im Sommer die Kieselalge Fragilaria crotonensis vermehrt durch Cyanobakterien verdrängt, was jedoch gut mit den Änderungen der hydrophysikalischen Struktur erklärt werden kann. Obwohl seit 1990 insgesamt mehr Phytoplankton zur Verfügung steht konnte das Crustaceen- Zooplankton in der Talsperre Saidenbach nicht von diesen verbesserten Nahrungsbedingungen profitieren. Die Daphnia-Abundanzen waren seit 1990 stark verringert. Es konnte gezeigt werden, dass der Einfluss des Fischbesatzes unterschätzt wurde und die künstlich ins System eingebrachten Silberkarpfen zeitweise bis zu 70% der zooplanktivoren Fischbiomasse ausgemacht haben. Zoo- planktivore Fische haben einen temperatur- und dichteabhängigen Effekt auf das Zooplankton. Das schnellere Populationswachstum von Daphnia kann bei hohem Besatz mit zooplanktivoren Fischen nicht die erhöhte Fraßaktivität der Fische ausgleichen. Dennoch konnte Temperatur als der wichtigste Einflussfaktor auf die Phänologie des Zooplanktons identifiziert werden, gefolgt von zooplanktivorem Fisch und Nährstoffzufuhr. Die Wichtigkeit von submersen Makrophyten in Flachseen ist gut untersucht. Um den Einfluss von Makropyhten auf die Wasserqualität während des Klimawandels auch in tiefen Seen abschätzen zu können, wurde ein komplexes Seemodell entwickelt. Die Simulationen zeigen, dass sich Makrophyten hauptsächlich positiv auf die Wassergüte auswirken und zur Reduktion von Phytoplankton, insbesondere von Cyanobakterien im Sommer, beitragen. In einem 11 m tiefen See betrug die Reduktion 50 %, in 100 m tiefen oligotrophen Seen immer noch 15 %. Die Konkurrenz um Nährstoffe mit dem Phytoplankton war dabei die ursächliche Makrophyten-Plankton-Interaktion. Submerse Makrophyten könnten für die Restaurierung von tiefen Seen folglich genauso wichtig sein, wie für Flachseen. Das komplette Seemodell enthält hydrophysikalische und ökologische Module und ermöglicht damit weitere umfassende Simulationen zur Untersuchung der Auswirkungen des Klimawandels und zur Evaluation von Adaptionsstrategien für Seen und Talsperren.

Made available in DSpace on 2016-06-02T19:29:50Z (GMT). No. of bitstreams: 1 TeseSPG.pdf: 896184 bytes, checksum: 0237c1553b20f09b9264cf38e782d113 (MD5) Previous issue date: 2004-06-30 / The influence of phytoplankton and their excreted materials in natural waters have been considered important issues among metal speciation studies. This work focused on the potential influence of the high molecular weight materials excreted by dominant phytoplankton species of Barra Bonita reservoir (Anabaena spiroides, Microcystis aeruginosa and Aulacoseira granulata) in the speciation and complexation of Cu and Cd. Therefore, this study comprised field and laboratory studies. Seasonal samplings were made during a period of two years in the reservoir. The total, ionic and organic concentrations of Cu and Cd were determined, as well as the complexation parameters with ligands present in the reservoir water. Also, the dissolved organic carbon and physico-chemical parameters of the water column were obtained. A speciation model was applied to metal complexation parameters and total metal concentrations obtained in field investigations. Laboratory cultures of the selected microalgae were made to obtain high molecular weight excreted materials. In a similar manner, the high molecular weight materials were isolated from the reservoir water. These materials were analysed for metal complexation with Cu and Cd, monosaccharide composition and elemental analysis (C, H, N and S). In the reservoir water, Cd speciation was dominated by ionic species, while Cu was mostly associated to the dissolved organic matter. Seasonal samplings presented Cu ligands with similar complexation parameters for the entire period studied. Cd complexation was not detected in the reservoir water. The speciation model resulted in similar Cu2+ concentration to the mean value obtained in field analyses, and indicated higher Cu association to the ligands of the reservoir water. Cu was complexed by all high molecular weight materials studied, while Cd was complexed solely by the cyanophyte materials. Higher proportions of acid monosaccharides in the high molecular weight materials corresponded to higher Cu and Cd complexation parameters, whereas no relation between C, H, N and S proportions and metal complexation properties of the high molecular weight materials was observed. The excreted materials of dominant microalgae from Barra Bonita reservoir had Cu ligands with intermediate to weak binding strength, as those present in the reservoir water. These results indicate the potential influence of such organic materials in metal speciation, bioavailability and mobility of metals with similar behaviour to that of Cu in the reservoir water. / A influência do fitoplâncton e de seus produtos excretados resultantes da fotossíntese em corpos d'água têm sido o enfoque de vários trabalhos que investigam a especiação e o destino de metais. Este estudo teve como hipótese a potencial influência dos materiais de alta massa molecular excretados por três espécies fitoplanctônicas (Anabaena spiroides, Microcystis aeruginosa e Aulacoseira granulata), dominantes no reservatório de Barra Bonita, em relação à especiação e complexação dos metais Cu e Cd na água do reservatório. Para tanto o estudo foi dividido em investigações de campo e experimentos de laboratório. Coletas sazonais por um período de dois anos no reservatório foram avaliadas quanto às espécies dissolvidas totais, orgânicas e iônicas de Cu e Cd, a determinação dos parâmetros de complexação destes metais com ligantes presentes na água, assim como o conteúdo de carbono orgânico dissolvido e os parâmetros físico-químicos da coluna d água. Uma modelagem da especiação química dos metais estudados foi feita com o uso das concentrações totais e os parâmetros de complexação adquiridos nas coletas sazonais. No laboratório foram obtidos os materiais de alta massa molecular excretados em cultivos das microalgas selecionadas, e o material de alta massa molecular dissolvido na água do reservatório, isolado seguindo-se o mesmo procedimento usado para os excretados algais. Estes materiais foram analisados quanto aos parâmetros de complexação com Cu e Cd, e composição monossacarídica e elementar (C, H, N e S). A especiação do Cd na água do reservatório foi dominada por formas iônicas, enquanto o Cu estava em grande maioria associado à matéria orgânica dissolvida. A água do reservatório apresentou, nas coletas sazonais, ligantes para Cu com parâmetros de complexação semelhantes em todo o período estudado. Nas condições experimentais empregadas, não foi detectada a complexação de Cd com ligantes oriundos da água do reservatório. A modelagem da especiação de Cu resultou em uma concentração semelhante de Cu2+ àquela medida em amostras de campo, e maior associação do Cu aos ligantes caracterizados neste estudo. O Cu foi complexado tanto pelos materiais de alta massa molecular das microalgas como também pela água do reservatório, enquanto o Cd foi complexado somente pelo material excretado pelas cianofíceas. Maiores proporções de monossacarídeos ácidos nos materiais corresponderam a parâmetros de complexação de Cu e Cd com valores mais elevados. No entanto, não foi observada uma relação entre as proporções de C, H, N e S e a complexação dos metais. Os excretados das microalgas dominantes no reservatório apresentaram ligantes para Cu com força de associação de intermediária a fraca, assim como os ligantes presentes no reservatório. Estes resultados confirmam o potencial de influência dos excretados na especiação, mobilidade e destino de metais com comportamento semelhante ao Cu, no reservatório de Barra Bonita.

Climate change affects lake ecosystems in many ways by direct and indirect temperature impacts on hydrophysical structure, hydrology, chemical cycles and on biological interactions. The identification of these climate signals can be complicated and superimposed by other environmental changes, such as land use changes. The aim of this thesis was to seperate temperature effects from effects of management and other environmental influences and to understand the underlying complex processes causing significant changes of ecosystem states. This understanding is important for decisions of lake and reservoir managers to counteract unfavorable consequences of climate change. For the recent study, long-term data of meteorological, hydrophysical and biological variables (phytoplankton, crustacean zooplankton, fish) of the German drinking water reservoir Saidenbach were analysed. Based on this long-term data set, strong indicators for climate induced changes have been identified. In particular, increasing water temperatures since 1975, earlier break up of ice covers and an altered hydrophysical structure could be detected. Thereby, stratification stability increased and turbulent mixing decreased in summer. The water of the reservoir warmed more than the tributaries resulting in a trend to deeper entrainment of the inflows. As further indicators of climate change, an increased annual biomass of phytoplankton and species shifts in the phytoplankton community in spring and summer had been observed. During the spring mass development, the diatom Aulacoseira subarctica became dominant in recent years with warm winters and early ice-out. Its unusual spatial pattern with occurrences in aphotic depths could be explained by easier resuspension compared to other diatoms. By being resuspended first and establishing a high inoculum, A. subarctica profits from an earlier ice-out and earlier full circulation. In spite of a reduced nutrient loading to the epilimnion, in summer, the diatom Fragilaria crotonensis was displaced increasingly by cyanobacteria. This species shift could be explained well by the hydrophysical regime shift. Although, the annual total phytoplankton biomass increased since 1990, the crustacean zooplankton in Saidenbach reservoir did not seem to profit from improved food resources. To the contrary, Daphnia abundances reduced tremendously. We could show that the influcence of fish stocks were underestimated. The stocked silvercarp may have contributed up to 70 % of the total zooplanktivorous fish biomass which had a temperature and density dependent effect. The faster growth of Daphnia at higher temperatures could not compensate for the more actively grazing fish when stock of zooplankitvorous fish was too high. Still, temperature was identified as the most important factor that explained 29 % of the zooplankton phenology, while the second most important predictors were zooplanktivorous fish biomass and nutrient loading, explaining 18 % of the variance. The importance of submerged macrophytes in shallow lakes is well investigated. To increase also the understanding of their impact and their role during climate change on water quality in deep lakes, a model for stratified lakes that includes submerged macrophytes was developed. The simulations showed that macrophyte effects were mainly positive for water quality and macrophytes in deep lakes were able to potentially reduce summer phytoplankton, especially cyanobacteria by 50 % in 11 m deep and still by 15 % in 100 m deep oligotrophic lakes. Nutrient competition with phytoplankton contributed most to this macrophyte effect. In conclusion, for deep lake restoration the re-establishment of submerged macrophytes might be as important as for shallow lakes. The full lake model includes hydrophysical and ecological submodules and thus will allow further comprehensive climate simulations and the evaluation of the effectivity of adaptive strategies and scenarios for deep lakes and reservoirs. / Der Klimawandel beeinflusst Seeökosysteme vielfältig durch direkte und indirekte Temperatureffekte auf die hydrophysikalische Struktur, die Hydrologie, chemische Kreisläufe und biologische Interaktionen. Die Identifikation von Klimasignalen kann durch Landnutzungs- und weitere Umweltveränderungen überlagert werden. Ziel dieser Arbeit war es, Temperatureffekte von Effekten zu unterscheiden, die durch Gewässermanagement oder anderen Umweltveränderungen verursacht werden. Weiterhin sollten komplexe Prozesse verstanden werden, die zu signifikanten Veränderungen in Seeökosystemen führen. Dieses Verständnis ist für Talsperren- und Gewässermanager von besonderer Bedeutung, um ungewünschten Folgen des Klimawandels entgegenwirken zu können. Für die Studie wurden Langzeitdaten für meteorologische, hydrophysikalische und biologische Variablen (Phytoplankton, Crustaceen-Zooplankton, Fischbesatz) der Talsperre Saidenbach ausgewertet. Mehrere Indikatoren für die Auswirkungen des Klimawandels konnten basierend auf diesen Daten identifiziert werden. Diese gehören insbesondere eine Erhöhung der Wassertemperatur seit 1975, zeitigere Eisaufbrüche und eine veränderte Schichtungsstruktur. Dabei wurde im Sommer die Schichtungsstabilität höher und die Intensität der Durchmischung geringer. Das Wasser in der Talsperre erwärmte sich stärker als die Zuflüsse, wodurch diese sich zunehmend tiefer und unterhalb der Thermokline einschichten. Eine zunehmende jährliche Phytoplanktonbiomasse und Artenwechsel innerhalb der Planktongemeinschaft sind weitere Indikatoren für Klimafolgen. Die Kieselalge Aulacoseira subarctica erlangte in Jahren mit warmen Wintern und zeitigen Eisaufbrüchen eine Dominanz während der Frühjahrsentwicklung. Das ungewöhnliche Auftreten dieser Art in aphotischen Tiefen konnte durch eine leichtere Resuspension im Vergleich zu anderen Kieselalgen erklärt werden. Durch zeitige Resuspension gleich nach Eisaufbruch kann A. subarctica ein hohes Inokulum etablieren. Trotz reduzierter Nährstoffzufuhr ins Epilimnion wurde im Sommer die Kieselalge Fragilaria crotonensis vermehrt durch Cyanobakterien verdrängt, was jedoch gut mit den Änderungen der hydrophysikalischen Struktur erklärt werden kann. Obwohl seit 1990 insgesamt mehr Phytoplankton zur Verfügung steht konnte das Crustaceen- Zooplankton in der Talsperre Saidenbach nicht von diesen verbesserten Nahrungsbedingungen profitieren. Die Daphnia-Abundanzen waren seit 1990 stark verringert. Es konnte gezeigt werden, dass der Einfluss des Fischbesatzes unterschätzt wurde und die künstlich ins System eingebrachten Silberkarpfen zeitweise bis zu 70% der zooplanktivoren Fischbiomasse ausgemacht haben. Zoo- planktivore Fische haben einen temperatur- und dichteabhängigen Effekt auf das Zooplankton. Das schnellere Populationswachstum von Daphnia kann bei hohem Besatz mit zooplanktivoren Fischen nicht die erhöhte Fraßaktivität der Fische ausgleichen. Dennoch konnte Temperatur als der wichtigste Einflussfaktor auf die Phänologie des Zooplanktons identifiziert werden, gefolgt von zooplanktivorem Fisch und Nährstoffzufuhr. Die Wichtigkeit von submersen Makrophyten in Flachseen ist gut untersucht. Um den Einfluss von Makropyhten auf die Wasserqualität während des Klimawandels auch in tiefen Seen abschätzen zu können, wurde ein komplexes Seemodell entwickelt. Die Simulationen zeigen, dass sich Makrophyten hauptsächlich positiv auf die Wassergüte auswirken und zur Reduktion von Phytoplankton, insbesondere von Cyanobakterien im Sommer, beitragen. In einem 11 m tiefen See betrug die Reduktion 50 %, in 100 m tiefen oligotrophen Seen immer noch 15 %. Die Konkurrenz um Nährstoffe mit dem Phytoplankton war dabei die ursächliche Makrophyten-Plankton-Interaktion. Submerse Makrophyten könnten für die Restaurierung von tiefen Seen folglich genauso wichtig sein, wie für Flachseen. Das komplette Seemodell enthält hydrophysikalische und ökologische Module und ermöglicht damit weitere umfassende Simulationen zur Untersuchung der Auswirkungen des Klimawandels und zur Evaluation von Adaptionsstrategien für Seen und Talsperren.

Since 1750, human emissions of greenhouse gases have created a temperature increase, affecting the whole world. Diatoms, single-celled microscopic algae that lives in waters all over the world, have different environmental preferences such as the water depth at which the thrive, salinity, nutrients, pH-values and more. Diatoms also responds quickly to changing circumstances, which makes the suitable as environmental indicators. The purpose of the study is to investigate how the abundance and composition of diatoms has changed during the last 200 years in lake Ensjön, located just south of Norrköping, and to relate those changes both to climate change and known events and environmental factors in the area.  The survey is conducted by subsampling sediment cores from which each diatom sample was prepared in accordance with the scheme of Battarbee (1984). The diatoms in the samples were counted under a microscope and the results were analyzed and related to the Cyclotella-Aulacoseira-Fragilaria-theory (CAF) and documented historical events in the local environment. The result of the analysis shows that the composition and abundance of diatoms has changed during the last 200 years, and that this change is due to both climate change (temperature and precipitation increase) and the land-use history of Ensjön. The cahnges in composition of Aulacoseira spp. and Cyclotella spp., where Aulacoseira spp. is expected to decrease, and Cyclotella spp. is expected to increase with a rising temperature, match the CAF-theory for the most part. The change in composition also coincides with several documented environmental factors in the area, especially the change in use of fertilizers and herbicides in agriculture. / Människans utsläpp av växthusgaser har sedan år 1750 skapat en temperaturökning som går allt snabbare, och påverkar hela världen. Kiselalger, encelliga mikroskopiska alger som lever i vatten över hela världen, har olika miljöpreferenser såsom bland annat på vilket vattendjup de trivs, optimal halt av salt, näringsvärden, pH-värden, samt reagerar snabbt på förändrade omständigheter, vilket gör dem lämpliga som miljöindikatorer. Syftet med studien är att studera förändringar i kiselalgernas sammansättning under de senaste 200 åren i den lilla sjön Ensjön belägen något söder om Norrköping och att relatera dessa förändringar till dokumenterade händelser och miljöfaktorer i sjöns avrinningsområde samt till de pågående klimatförändringarna.  Undersökningen är utförd genom provtagning av sedimentkärnor från vilka prover preparerades enligt Battarbees (1984) flödesschema. Proverna av kiselalger räknades under mikroskop och sammansättningen analyserades utifrån teorin Cyclotella-Aulacoseira-Fragilaria (CAF) och kända historiska händelser i närmiljön. Analysresultatet visade att kiselalgssammansättningen har förändrats under de senaste 200 åren, och att denna förändring sannolikt kan kopplas både till klimatförändringar (en ökad temperatur) och Ensjöns markanvändningshistoria. Förändringen hos Aulacoseira spp. och Cyclotella spp. följer till stor del CAF-teorin om att det första släktet skulle minska och det andra skulle öka vid en temperaturökning. Vid flera tillfällen sammanfaller förändringar i kiselalgssammansättningen med kända miljöfaktorer i närmiljön, främst i samband med utvecklingen i användningen av mineralgödsel och växtskyddsmedel.