Lake Skärsjön is a dimictic, oligotrophic, clear water lake with bottom plant communities including the rare Nostoc zetterstedtii. The lake is located in western Sweden, south of Gothenburg. During the late 1970s to mid-1980s, there was fish cage farming located near the outlet of the lake. When the fish farming was first introduced, there was concern over the health of the late which prompted a monitoring study which was conducted from 1980 to 1990 by the County Administration Board (regional governing body of Sweden). Starting in 1983, another National Monitoring study commenced simultaneously with the 10 year study. This monitoring study had one site taking measurements from 0.2-2m and collected the same data as the 10 year study. There were notable changes starting in 1985, the year the fish farming was closed down. After these changes, there are patterns indicating the lake returning to similar conditions before 1985. The pH of the lake is increasing and the acidity decreasing which reflects the ongoing decrease in atmospheric sulphur deposition and concentration in the lake. Overall, the impacts from the fish farming may have been more intense if it was located farther from the lake outlet. This would have allowed nutrient emissions from the fish cages to influence the lake more severely before exiting through the outlet. The lake is slowly recovering from this anthropogenic event and the current monitoring program, the National Monitoring study, should remain intact.

This study is designed to (a) demonstrate the highly productive nature of the littoral area as compared to the pelagic region, (b) the possible importance of phyco-periphyton in the diets of fish, (c) the effects of meteorological conditions on distribution of phytoplankton, and (d) a demonstration of the invalidity of using artificial substrates as a universal means of measuring productivity.

The greater Everglades ecosystem, including Florida Bay, has undergone significant anthropogenic manipulation over the past century. These actions resulted in a series of ecologically undesirable events in the Everglades ecosystem, prompting passage of the Comprehensive Everglades Restoration Plan (CERP). It is necessary to understand the variability in, and relationship between, salinity and ecology to fully evaluate the potential effects of CERP on Florida Bay. A seven-year dataset on surface salinity along with eleven-year and eight-year datasets on mesozooplankton and planktivorous fish were analyzed. Overall, mean Bay-wide salinity varied from a low of 24.2 just after the passing of Hurricane Irene in October 1999 to a high of 41.8 near the end of a drought period in July 2001. Bay-wide mean salinity exhibited dramatic decreases, up to 0.5 per day, whereas increases in bay-wide salinity were slower, with a maximum rate of 0.1 per day. Meteorological phenomena, such as tropical cyclones and ENSO, dramatically altered the salinity patterns of Florida Bay on interannual time scales. There was a large degree of spatial heterogeneity in salinity between sub-regions of Florida Bay due to differing freshwater sources and geomorphology. Mesozooplankton abundance displayed interannual variability and a positive correlation with salinity. Both of these features were also closely correlated with abundance of the dominant planktivorous fish, Anchoa mitchilli, indicating the importance of top-down control. The hypersaline periods appear to provide a refuge from predators, allowing mesozooplankton to increase in abundance during periods of increased physiological stress. The interaction between mesozooplankton and A. mitchilli, along with its correlation to salinity, was further investigated through the development of a mechanistic model of the populations in Florida Bay. The model indicated predation alone was insufficient to control mesozooplankton populations; rather, it was necessary to incorporate density-dependence utilizing a logistic prey population. With both mechanisms the model was able to replicate the observed interannual variability pattern and positive correlation between mesozooplankton and salinity. A preliminary management scenario evaluation suggests a two to six-fold difference in A. mitchilli and mesozooplankton populations between targeted and general salinity reductions. This suggests alternative freshwater management scenarios could produce drastically different ecological consequences.

In a climate change perspective, increased air temperatures are already a reality and are expected to increase even more in the future, especially in areas at high latitudes. The present thesis therefore addresses the influence of climate change on the physical properties and the phytoplankton communities of typical small and oligotrophic lakes in northern Sweden (62-64˚N). In the first part of the study, we found a significant trend (10 lakes from 1916 to 2010) of ice break-ups occurring increasingly earlier. The timing of ice break-up was strongly influenced by the April air temperature indicating that expected increases in air temperature in the future will also result in an earlier ice break-up. We also used concentrations of chlorophyll a (chl a) as estimations of phytoplankton biomass and discovered a positive relationship between surface water temperature and concentrations of chl a in Lake Remmaren (from 1991 to 2008). The second part of the thesis focuses on climatic conditions and cyanobacteria abundance in three small, oligotrophic lakes in northern Sweden; Lake Remmaren, Lake S. Bergsjön and Lake Gransjön. The concentration and relative abundance of cyanobacteria differ between 2011 and 2012, with different climatic conditions. The "warm" year of 2011 had higher concentrations and relative abundance of cyanobacteria than the "cold" year of 2012. Trends in increasing surface water temperatures as well as increasing abundance of cyanobacteria in August were found in Lake Remmaren (from 1988 to 2011). The direct or indirect effects of warming had a positive effect on the cyanobacteria abundance, since nutrients (Tot N and Tot P) did not display an increasing trend in Lake Remmaren. An analysis on the composition of phytoplankton species in Lake Remmaren, Lake S. Bergsjön and Lake Gransjön revealed that the cyanobacteria Merismopedia sp. was more common in 2011 than 2012. If different cyanobacteria become more common in oligotrophic lakes in the future, the functioning of lake ecosystems may be impacted. Small zooplankton eats small phytoplankton and if smaller phytoplankton species, e.g. cyanobacteria, increase at the expense of other phytoplankton groups, an extra step in the food chain might be added. Less energy might be transferred to the upper levels because many cyanobacteria contain toxic compounds and are less edible than other phytoplankton groups. An increase of toxic containing cyanobacteria in lakes can also make lakes less attractive for recreational purposes in the future.

No description available.

Poor food quality can have large negative effects on zooplankton growth and this can also affect food web interactions. The main aims of this thesis were to study the importance of different food quality aspects in Daphnia, to identify potentially important differences among zooplankton taxa, and to put food quality research into a natural context by identifying the importance of food quality and quantity in lakes of different nutrient content. In the first experiment, the RNA:DNA ratio was positively related to the somatic growth rate of Daphnia, supporting a connection between P content, RNA content, and growth rate. The second experiment showed that EPA was important for Daphnia somatic growth, and 0.9 µg EPA mg C-1 was identified as the threshold below which negative effects on Daphnia growth occurred. A field survey identified patterns in the PUFA content of zooplankton that could be explained by taxonomy and trophic position. Cladocera enriched EPA and ARA relative to seston, and Copepoda primarily enriched DHA. In a whole-lake experiment, gentle fertilization of an oligotrophicated reservoir increased the seston P content and the biomass of high quality phytoplankton (Cryptophyceae, high EPA content). This was followed by increases in zooplankton and fish biomasses. An empirical model based on data from a literature survey predicted that food quantity is most important for zooplankton growth in oligotrophic lakes, and that food quality factors are more important in eutrophic lakes. Thus, zooplankton growth, and energy transfer efficiency in the food web, is predicted to be highest in mesotrophic lakes. The results predict that the strength and nature of food quantity and quality limitation of Daphnia growth varies with lake trophic state, and that some combination of food quantity and/or quality limitation should be expected in nearly all lakes.

O perifíton é formado por uma complexa comunidade de organismos aderidos a um substrato orgânico ou inorgânico, dos quais as diatomáceas (Bacillariophyta) constituem importante parcela. Mais recentemente inventários florísticos que contemplam as diatomáceas bentônicas em sistemas lóticos vêm incrementando o conhecimento da flora na região Neotropical e Neosubtropical, porém grande parte desses sistemas permanece inexplorado, especialmente em águas oligotróficas, de altitude e de baixo pH. Tais ecossistemas em geral possuem uma flora bastante peculiar, e são importantes referências em termos qualidade de água. Desta forma, o presente estudo teve por objetivos contribuir para o conhecimento da flora de diatomáceas perifíticas do Parque Estadual do Ibitipoca, localizado na serra da Mantiqueira em Minas Gerais. Como resultado, foram identificados 15 gêneros, 18 espécies e duas variedades taxonômicas. Duas novas espécies do gênero Eunotia são propostas e três espécies do gênero Nupela não puderam ser identificadas de acordo com a literatura, sendo provavelmente novas para a ciência. São feitos 16 registros pioneiros para o estado de Minas Gerais, sendo quatro delas primeiras ocorrências em território brasileiro. A composição taxonômica das diatomáceas perifíticas do Parque Estadual do Ibitipoca apresenta semelhanças com a flora de outros ambientes oligo-distróficos já inventariados nos Neotrópicos. Palavras-chave: ambientes continentais, águas oligotróficas, Eunotia, Nupela, taxonomia de criptógamos. / The periphyton is composed by a complex community of organisms adhered to an organic or inorganic substrate, and diatoms (Bacillariophyta) constitute an important part of it. More recent floristic inventories in lotic systems that include benthic diatoms increased the knowledge of the Neosubtropical Neotropical flora for the region, but most environments remains unexplored, especially those with oligotrophic and low pH waters in altitude sites. Such ecosystems in general have a very peculiar flora and are important indicators of water quality. Thus, the present study aimed to contribute to the knowledge of periphytic diatom flora of Ibitipoca State Park, located in the Mantiqueira ridge, in Minas Gerais. As a result, we identified 15 genera, 18 species and two taxonomic varieties. Two new species of Eunotia are proposed and three species of the genus Nupela could not be identified according to the literature, and are probably new to science. Sixteen new records were made for the state of Minas Gerais, including four first occurrences for Brazil. The taxonomic composition of the periphytic diatoms of Ibitipoca State Park share similarities with other oligo-dystrophic environments already surveyed in the Neotropics.

<p>Poor food quality can have large negative effects on zooplankton growth and this can also affect food web interactions. The main aims of this thesis were to study the importance of different food quality aspects in <i>Daphnia</i>, to identify potentially important differences among zooplankton taxa, and to put food quality research into a natural context by identifying the importance of food quality and quantity in lakes of different nutrient content.</p><p>In the first experiment, the RNA:DNA ratio was positively related to the somatic growth rate of <i>Daphnia</i>, supporting a connection between P content, RNA content, and growth rate. The second experiment showed that EPA was important for <i>Daphnia</i> somatic growth, and 0.9 µg EPA mg C^-1 was identified as the threshold below which negative effects on <i>Daphnia</i> growth occurred.</p><p>A field survey identified patterns in the PUFA content of zooplankton that could be explained by taxonomy and trophic position. <i>Cladocera</i> enriched EPA and ARA relative to seston, and <i>Copepoda</i> primarily enriched DHA. In a whole-lake experiment, gentle fertilization of an oligotrophicated reservoir increased the seston P content and the biomass of high quality phytoplankton (<i>Cryptophyceae</i>, high EPA content). This was followed by increases in zooplankton and fish biomasses.</p><p>An empirical model based on data from a literature survey predicted that food quantity is most important for zooplankton growth in oligotrophic lakes, and that food quality factors are more important in eutrophic lakes. Thus, zooplankton growth, and energy transfer efficiency in the food web, is predicted to be highest in mesotrophic lakes. The results predict that the strength and nature of food quantity and quality limitation of <i>Daphnia</i> growth varies with lake trophic state, and that some combination of food quantity and/or quality limitation should be expected in nearly all lakes.</p>

O perifíton é formado por uma complexa comunidade de organismos aderidos a um substrato orgânico ou inorgânico, dos quais as diatomáceas (Bacillariophyta) constituem importante parcela. Mais recentemente inventários florísticos que contemplam as diatomáceas bentônicas em sistemas lóticos vêm incrementando o conhecimento da flora na região Neotropical e Neosubtropical, porém grande parte desses sistemas permanece inexplorado, especialmente em águas oligotróficas, de altitude e de baixo pH. Tais ecossistemas em geral possuem uma flora bastante peculiar, e são importantes referências em termos qualidade de água. Desta forma, o presente estudo teve por objetivos contribuir para o conhecimento da flora de diatomáceas perifíticas do Parque Estadual do Ibitipoca, localizado na serra da Mantiqueira em Minas Gerais. Como resultado, foram identificados 15 gêneros, 18 espécies e duas variedades taxonômicas. Duas novas espécies do gênero Eunotia são propostas e três espécies do gênero Nupela não puderam ser identificadas de acordo com a literatura, sendo provavelmente novas para a ciência. São feitos 16 registros pioneiros para o estado de Minas Gerais, sendo quatro delas primeiras ocorrências em território brasileiro. A composição taxonômica das diatomáceas perifíticas do Parque Estadual do Ibitipoca apresenta semelhanças com a flora de outros ambientes oligo-distróficos já inventariados nos Neotrópicos. Palavras-chave: ambientes continentais, águas oligotróficas, Eunotia, Nupela, taxonomia de criptógamos. / The periphyton is composed by a complex community of organisms adhered to an organic or inorganic substrate, and diatoms (Bacillariophyta) constitute an important part of it. More recent floristic inventories in lotic systems that include benthic diatoms increased the knowledge of the Neosubtropical Neotropical flora for the region, but most environments remains unexplored, especially those with oligotrophic and low pH waters in altitude sites. Such ecosystems in general have a very peculiar flora and are important indicators of water quality. Thus, the present study aimed to contribute to the knowledge of periphytic diatom flora of Ibitipoca State Park, located in the Mantiqueira ridge, in Minas Gerais. As a result, we identified 15 genera, 18 species and two taxonomic varieties. Two new species of Eunotia are proposed and three species of the genus Nupela could not be identified according to the literature, and are probably new to science. Sixteen new records were made for the state of Minas Gerais, including four first occurrences for Brazil. The taxonomic composition of the periphytic diatoms of Ibitipoca State Park share similarities with other oligo-dystrophic environments already surveyed in the Neotropics.

O perifíton é formado por uma complexa comunidade de organismos aderidos a um substrato orgânico ou inorgânico, dos quais as diatomáceas (Bacillariophyta) constituem importante parcela. Mais recentemente inventários florísticos que contemplam as diatomáceas bentônicas em sistemas lóticos vêm incrementando o conhecimento da flora na região Neotropical e Neosubtropical, porém grande parte desses sistemas permanece inexplorado, especialmente em águas oligotróficas, de altitude e de baixo pH. Tais ecossistemas em geral possuem uma flora bastante peculiar, e são importantes referências em termos qualidade de água. Desta forma, o presente estudo teve por objetivos contribuir para o conhecimento da flora de diatomáceas perifíticas do Parque Estadual do Ibitipoca, localizado na serra da Mantiqueira em Minas Gerais. Como resultado, foram identificados 15 gêneros, 18 espécies e duas variedades taxonômicas. Duas novas espécies do gênero Eunotia são propostas e três espécies do gênero Nupela não puderam ser identificadas de acordo com a literatura, sendo provavelmente novas para a ciência. São feitos 16 registros pioneiros para o estado de Minas Gerais, sendo quatro delas primeiras ocorrências em território brasileiro. A composição taxonômica das diatomáceas perifíticas do Parque Estadual do Ibitipoca apresenta semelhanças com a flora de outros ambientes oligo-distróficos já inventariados nos Neotrópicos. Palavras-chave: ambientes continentais, águas oligotróficas, Eunotia, Nupela, taxonomia de criptógamos. / The periphyton is composed by a complex community of organisms adhered to an organic or inorganic substrate, and diatoms (Bacillariophyta) constitute an important part of it. More recent floristic inventories in lotic systems that include benthic diatoms increased the knowledge of the Neosubtropical Neotropical flora for the region, but most environments remains unexplored, especially those with oligotrophic and low pH waters in altitude sites. Such ecosystems in general have a very peculiar flora and are important indicators of water quality. Thus, the present study aimed to contribute to the knowledge of periphytic diatom flora of Ibitipoca State Park, located in the Mantiqueira ridge, in Minas Gerais. As a result, we identified 15 genera, 18 species and two taxonomic varieties. Two new species of Eunotia are proposed and three species of the genus Nupela could not be identified according to the literature, and are probably new to science. Sixteen new records were made for the state of Minas Gerais, including four first occurrences for Brazil. The taxonomic composition of the periphytic diatoms of Ibitipoca State Park share similarities with other oligo-dystrophic environments already surveyed in the Neotropics.