Externe Einträge von Nährstoffen, vor allem von Phosphor, fördern die Phytoplanktonentwicklung und sind damit die primäre Ursache für die Verschlechterung der Gewässergüte in Seen. Die pelagische Nahrungsnetzstruktur kann dabei sowohl positiv als auch negativ auf die Gewässergüte einwirken. Deshalb lässt sich der Gewässerzustand durch eine gezielte Steuerung der Räuber-Beute-Verhältnisse verändern. In der vorliegenden Arbeit wurden Ergebnisse der Groß-Enclosure-Experimente zu den Auswirkungen von Nährstoffen (mit/ohne Zugabe von Nährstoffen) sowie von einer manipulierten Nahrungsnetzstruktur (mit/ohne Zugabe von planktivoren Fischen) auf die pelagische Phyto- und Zooplanktongemeinschaft eines thermisch geschichteten Sees (Dagowsee, Brandenburg) präsentiert. Im Schwerpunkt der Untersuchungen lagen dabei die qualitativen und quantitativen Effekte dieser beiden Faktoren auf die Sedimentationsprozesse sowie den mikrobiellen Umsatz von Kohlenstoff und Phosphor im Hypolimnion und an der Sediment-Wasser-Kontaktzone des Sees. Es wurde gezeigt, dass die Manipulation der Nahrungsnetzstruktur sich auf die Menge und Zusammensetzung des Phyto- und Zooplanktons im Epilimnion des Sees sowie auf den quantitativen vertikalen Transport von Kohlenstoff und Phosphor auswirkte, während die unterschiedliche Nährstoffbelastung im Epilimnion die spezifischen Stoffgehalte des Kohlenstoffs und Phosphors im sedimentierten Material beeinflussten. Anhand der Sauerstoff- und Methanmessungen wurde festgestellt, dass die Intensität des mikrobiellen Abbaus der sedimentierten organischen Substanz vor allem von ihrer Menge abhängig war. Weiterhin konnten die Auswirkungen der manipulierten Nahrungsnetzstruktur auf die Effizienz während des Abbaus vom organischen Kohlenstoff in den Laborversuchen nachgewiesen werden. Diese Effekte waren allerdings in den Freilandexperimenten schwer nachweisbar aufgrund der Beteiligung der Abbauprodukte in anderen oxidativ-reduktiven Prozessen, die gleichzeitig im See verliefen. Anhand des Phosphor-Fraktionierungsverfahrens konnte festgestellt werden, dass dieser Stoff nicht organisch sondern zum größten Teil an Eisen und Mangen gebunden sowie labil adsorbiert die Sedimentoberfläche erreichte. An dieser Stelle zeigten diese beiden Fraktionen einen systematischen Unterschied, der nur auf eine Wirkung der epilimnischen Nährstoffkonzentration und nicht auf die des manipulierten Nahrungsnetzes hinwies. Weitere Analysen der Sedimente zeigten starke Transformationen des sedimentierten Phosphors, aufgrund deren vor allem die dominierenden labilen und redoxsensitiven Phosphorfraktionen betroffen waren. Sie wurden zum einen ins Wasser zurückgelöst und zum anderen in die organische Biomasse gespeichert. Die Veränderungen des Phosphorgehaltes in den Sedimenten waren wieder auf die vorherigen Effekte der Nährstoffe als der manipulierten Nahrungsnetzstruktur zurückzuführen. Die Effekte der Nahrungsnetzmanipulation waren also vor allem an der pelagischen Planktongemeinschaft im Epilimnion und an den Sedimentations- und Kohlenumsatzprozessen in tieferen Schichten des Sees zu sehen. Der vertikale Phosphortransport wurde weniger von der Nahrungsnetzstruktur beeinflusst. Dafür spielte dabei die epilimnische Nährstoffkonzentration sowie die Phosphorbindungspotenzial des Wassers für den internen Kreislauf des Stoffes eine wichtige Rolle. / External load of nutrients, above all from phosphorus, promote the phytoplankton development and are with it the primary cause for the deterioration of the waters quality in lakes. Further, the pelagic food web structure can affect the water quality in a positive as well as in a negative way. Therefore, the water trophic state can be changed by a specific control of the predator-prey relations. In the present study the results of the large enclosure experiments to the impact by nutrients (with/without addition of nutrients) as well as by a manipulated food web structure (with/without addition of planktivorous fish) on the pelagic phyto- and zooplankton community of a thermally stratified lake (Dagowsee, Brandenburg) were presented. Furthermore, the qualitative and quantitative effects of these both factors on the sedimentation processes as well as the microbial turnover of settled carbon and phosphorus in the hypolimnion and at the sediment-water layer of the lake were in the main focus of the investigations. It has been shown that the manipulation of the food web structure affected the amount and composition of the phyto- and zooplankton in the epilimnion as well as the quantitative vertical transport of carbon and phosphorus, while the different nutrient load in the epilimnion influenced the specific material content of the carbon and phosphorus in the sedimented material. With the help of the oxygen and methane measurements it was found out that the intensity of the microbial decomposition of the settled organic matter was dependent above all on her quantity. Furthermore, the effects of the manipulated food web structure on the decomposition efficiency of the organic carbon could be proved in the laboratory tests. However, these effects were in the free land experiments hardly provably due to the participation of the endproducts in other redox processes which ran at the same time in the lake. With the help of the phosphorus fractionation procedure could be found out that settled phosphorus for the most part not organically but in iron and manganese bound as well as loosely adsorbed the sediment surface reached. At this point these both forms showed a systematic difference which pointed only to an effect of the epilimnetic nutrient concentration and not on those of the manipulated food web. Other analyses of the sediments showed strong transformations of the settled phosphorus, which influenced above all the dominating labile and redox sensitive phosphorus fractions. They were released, on the one hand, in the water and stored, on the other hand, in the organic biomass. The changes of the phosphorus content in the sediments were to be led on the previous effects of the nutrients than of the manipulated food web structure. To conclude, the effects of the food net manipulation were to be seen above all in the pelagic plankton community in the epilimnion, and further in sedimentation and carbon turnover processes in deeper layers of the lake. The vertical phosphorus transport was influenced of less by the food web structure. Moreover, for it the epilimnic nutrient concentration as well as the phosphorus binding potential of the water played an important role for the internal circulation of the material.

O gerenciamento dos estoques pesqueiros, um dos instrumentos da biomanipulação, deve ter início com a classificação das espécies existentes e sua diversidade, a estrutura da rede alimentar e as relações reguladoras, como a relação predador-presa. O lago Paranoá (Brasília - DF) é um reservatório urbano que sofre pressões antrópicas devido a seus usos múltiplos. Após a construção enchimento, sucessivas introduções de espécies ictíicas exóticas causaram um desequilíbrio que, associado às pressões descritas acima, geraram uma aceleração no processo de eutrofização deste ambiente. Desta forma, os objetivos deste trabalho foram: avaliar os impactos ambientais da introdução das espécies predadoras sobre a cadeia trófica e a qualidade da água do reservatório; determinar a eficiência das diferentes espécies de predadores no controle das presas nas áreas marginais da represa, discutindo possíveis estratégias de manejo pesqueiro baseadas na estocagem de peixes predadores. Para tanto foram construídos 10 limnocurrais com lonas impermeáveis numa baía localizada no ETE-Norte (Estação de tratamento de esgotos - Norte). Em seu interior, após a retirada de todos os peixes, foram estocadas por um período de 28 dias, duas espécies de predadores (Cichla ocellaris e Pseudoplatytoma fasciatum) e uma comunidade simplificada de presas (Tilapia rendalli e Oreochromis niloticus), acima da capacidade do suporte do sistema, definida em 4 classes de tamanho. As biomassas de estocagem foram determinadas a partir da aplicação de retenona em uma área com dimensões conhecidas, e extrapoladas para as áreas dos limnocurrais. As variáveis físicas e químicos da água foram acompanhados semanalmente durante o experimento. Não houve diferenças significativas entre os tratamentos, em relação às variáveis limnológicas. Quanto ao controle das presas, o tucunaré mostrou-se um predador eficiente em relação às classes de tamanhos menores ) (2 - 6,9 cm e 7 - 12,9 cm), fato não observado para o tratamento com surubim. De acordo com os resultados obtidos, não foi comprovada a hipótese de cascata trófica devido à complexidade das interações entre os organismos em ambientes tropicais. / The managing of the fish stocks, one of the tools of the biomanipulation, must begin with the classification of the present species and their diversity, of the structure of the food web and of the regulation relations (as the relation predator-prey).The Paranoá Lake (Brasília, DF) is an urban reservoir that suffers human pressures as a result of its multiple uses. After its construction and filling, the successive introduction of many fish exotic species resulted in an unbalance that, associated with the pressures described above, generated an acceleration in the eutrophication process of the ambient. In this way, the objectives of this work were: evaluate the environmental impacts from the introduction of the species predators in food web and quality from the reservoir\'s water; decide the efficiency of the species of predators in the prey\'s control in the marginal areas from dam, discussing possible fishing strategies of management based in the Stocking of fish predators. Them, 10 limnocorrals were built with waterproof canvases in a bay located in ETE-NORTE (sewers handling Station - North). In its interior, after retreat of all fishes, by a period of 28 days, two species of predators were stocked (Cichla ocellaris and Pseudoplatystoma coruscans), and a community simplified of prey (Tilapia rendalli and Oreochromis niloticus), above from the capacity of the system, defined in 4 classes of size. The biomasses of stocking were determined from application of rotenona in an area with known dimensions, and overstepped for the areas of the limnocorrals. The physical-chemists parameters from the water were accompanied weekly during the experiment. It had no significant differences between the handlings, regarding the variables limnological. As regards the control of prey, C. ocellaris showed itself an efficient predator regarding the smallest classes of sizes (2 - 6,9 cm and 7 - 12,9 cm), fact do not observe for the handling with P. coruscans. Agreement with the results obtained, was not verified to hypothesis of trophic cascade due to the complexity of the interactions between the agencies in tropical environments.

The Lower Karori Reservoir (LKR) is a small, monomictic lake of 2.34 ha situated in the Karori Wildlife Sanctuary (KWS), Wellington. Over the past decade cyanobacterial blooms have become a common occurrence in this water body. In 2005 Anabaena planktonica was detected for the first time in the LKR and this species now forms dense blooms during summer. These blooms are problematic as they reduce aesthetic appeal and have resulted in odour problems for visitors to this high profile wildlife sanctuary. The objectives of this study were to identify key physical, chemical and biological variables influencing phytoplankton dynamics in the LKR and to use ecological models to investigate plausible management options. The key parameters investigated, that may cause bloom formation were; summer stratification, high nutrient levels, and the food web effects of a large population of European perch (Perca fluviatilis). High resolution sampling was carried out every six hours over a 72 hour period during pre-bloom, bloom and post-bloom periods in 2006/7 to elucidate short term temporal and spatial variations in biological and physico-chemical parameters. Quantitative polymerase chain reaction (QPCR) was used to enumerate A. planktonica populations, allowing a large number of samples to be simultaneously evaluated. Algal densities were also estimated using conventional phytoplankton enumeration and chlorophyll a analysis. Water samples were collected for nutrient analysis at discrete depths and profiles were taken for temperature, dissolved oxygen and photosynthetic active radiation. Secchi depth and pH were also measured. Weekly or fortnightly phytoplankton and zooplankton samples and physical variables have been collected at LKR since September 2005 as part of an independent sampling program carried out by the KWS, Waikato University and Cawthron Institute. In this project the 2-year data set was used to assist with analysis of lake processes and for validation of the hydrodynamic-ecological model DYRESM-CAEDYM. Between 12 and 15 February, 2007, electric fishing was undertaken within the LKR. A total of 3,946 P. fluviatilis were removed and the effects on phytoplankton and zooplankton concentrations were investigated. To increase knowledge of the physiology of A. planktonica, laboratory experiments were undertaken using cultures subjected to a range of different light intensities and temperature regimes The phytoplankton assemblage of the LKR shows very distinct temporal variations. Summer stratification occurred in the LKR for ~4 months each summer. During these periods A. planktonica comprised up to 99.9% of the surface phytoplankton population. During isothermy chlorophytes, bacillariophytes and small flagellated dinophytes are co-dominant in the phytoplankton assemblage. The results of the QPCR showed distinct diurnal vertical movement of A. planktonica, with the highest cell concentrations occurring at 1900 hours at the surface. Ammonium (NH4-N) is the dominant species of inorganic nitrogen during periods of stratification, while nitrate (NO3-N) is generally dominant during times of isothermy. Phosphate concentrations at surface and depth remained at low levels throughout the sampling period. The large surface populations of A. planktonica, are probably responsible for the elevated total nitrogen concentrations in surface waters during stratified periods. There appeared to be some short term effects of the P. fluviatilis removal with an increase in large crustaceans (e.g., Daphnia sp.) and a reduction in A. planktonica densities observed in the months following the P. fluviatilis removal. Only a small proportion of the total P. fluviatilis population was removed and it is unlikely that the effects will be long-lasting without subsequent removal steps. However, it seems likely that P. fluviatilis is one of the factors contributing to cyanobacterial blooms and management of this fish species should be considered in future lake restoration plans. Growth experiments indicated A. planktonica grow over a wide range of light intensities and temperatures, although highest growth rates were generally associated with higher temperatures (25 C) and light intensities (60 - 140 μmol m-2 s-1). Ecological and hydrodynamic trends within the LKR over a two year period were simulated with adequate success using the model DYRESM-CAEDYM. Management scenarios simulated using DYRESM-CAEDYM suggest implementation of an artificial destratification system in the LKR may be the most practical and effective means of controlling A. planktonica blooms. The addition of an artificial aeration system emitting air at a rate of approximately 50 l-1 s-1 should result in an isothermal system. Without summer stratification some of the physiological features of A. planktonica (e.g., buoyancy regulation and nitrogen-fixation) that give it a competitive advantage over other phytoplankton species will be reduced.

Lake Waikare is a large, shallow eutrophic lake devoid of submerged macrophytes. I investigated potential methods for re-establishing submerged macrophytes in the lake. Specifically, I subjected charophyte (Chara corallina) plantlets to two treatments of exposure in the lake (in areas exposed and sheltered from wind) to test for survival and growth under these conditions, and inside and outside fish exclosures to test for growth and survival in the presence of fish. While plantlets grew outside the exclosures in winter, their accumulated biomass over 21 days was less than protected plantlets. In winter, the accumulated biomass was lower outside than inside exclosures (by ~40%) at the sheltered site and was lower outside than inside exclosures (by 43%) at the exposed site. Overall, growth rates in winter were higher at the sheltered site (compared to the exposed site) by ~7%. In summer, charophyte accumulated biomass inside the exclosures increased by 85%, while at the sheltered site accumulated biomass increased by 58%. Outside the exclosures in summer the plantlets were completely removed at both sites. Overall, growth rates where higher at the exposed site than the sheltered site by 31%. Fish were responsible for the partial removal of plantlets in winter and total removal of plantlets in summer, and therefore affect the survival and growth of charophytes in Lake Waikare. The embayment at the sheltered site provides the best location in winter for re-establishment of charophytes from oospores because better growth rates were obtained there, and its sheltered location provides protection from severe wave action found at the exposed site. Oospores did not germinate after being submersed in the lake for 90 days due to heavy sedimentation. To induce an improvement in the present light climate, Alum was tested to determine its effectiveness and longevity for settling lake sediments to allow charophytes to establish and grow. Examining the settling rates of Lake Waikare sediments and water treated with Alum over a range of suspended sediment concentrations and time intervals, sediments settled faster with Alum than without for at least 15 days (at 200 g l^1 suspended sediment concentration) and it remained active to 60 days but at reduced effectiveness. At the other concentrations tested (100 g l^1 and 300 g l^1 suspended sediment concentration), Alum responses were insignificant. An improved light climate achieved by fish removal or Alum treatment will likely not be sufficient to permit the re-establishment of submerged macrophytes due to the turbid, algal-dominated state of the lake. The present nutrient and sediment levels, wave climate and fish influence must be mitigated so charophyte plantlets can be established.

In this study, the hydrology and physical, chemical and biological variables of a shallow lake system including the Lakes Mogan and Eymir between 1997-2005 were evaluated. In Lake Eymir, a biomanipulation study was conducted between August, 1998 &ndash / December, 1999. Upon biomanipulation, Lake Eymir shifted to clearwater state with submerged vegetation domination during 2000-2003. However, in 2004, the lake shifted back to algae-dominated turbid state since the buffer mechanisms provided by submerged plants were absent. In the summer of 2005, fish kills were observed due to algal bloom. However, due to increasing hydraulic residence time in the lake, internal processes became more important for nutrients. Lake Mogan faces seasonal and interannual water level fluctuations. During the low water levels experienced in 2001 and 2005, which coincided with the high hydraulic residence times, the in-lake phosphorus amount was controlled by internal processes rather than external loading. Moreover, results revealed that hydrology and submerged plants were important in the ecology of Lake Mogan. Furthermore, the relationship between the phytoplankton, zooplankton and the environment in Lakes Eymir and Mogan, which was predicted via Canonical Corresponding Analysis, revealed that nutrients and water transparency were both important for plankton communities. Both the top-down and bottom up effects were valid in Lake Eymir, while only the bottom-up effect and submerged plants were important for Lake Mogan. Finally, the present study provided a good example for the submerged plant dominated clearwater state triggered by biomanipulation, and the impact of hydrology on the ecology of shallow lakes.

No description available.

The Chabařovice coal mining pit is currently still under the process of continuous flooding and its area increased up to 174 ha since 2001.Adult perch (Perca fluviatilis) have been the most numerous fish of the lake until 2004. Fish were collected during the ichtyological survey sampling campaigns in June and September.Diet composition was expressed as percent weight, which was calculated for each prey taxon.

The Chabarovice coal mining pit arose by flooding the former strip mine area for brown coal. After filling, the pit area should reach about 225 hectare, total volume of water 34.4 mil. m3, average depth 15,6 meters with maximum of 23,3meters. It is assumed that the pond and adjacent areas will be used for recreation usage after completion of recultivation and ground shaping. I have performed the investigations in June and in August 2004 - 2005, using basic ichthyological methods. The data about recruitment were collected by the littoral seine net and adult fish (older than one year) were investigated by gillnets nets. Fish was determinated to genus, individually measured by slide caliper (fry) and by measuring plate (adult fish). The lenght of fish body (SL-standart lenght) was measured in millimeters and fish were weighted separately (W v g). In the year 2005, also scales were taken from individual fish for the age assesment. Obtained data were processed with regard to performed biomanipulation measures in individual sectores. Nine fish species and one hybrid were recorded by the monitoring with gillnets nets. The most numerous fish were juveniles and adults of rudd with SL 74 {--} 300 mm and the weight up to 618 g. The fish species with the strongest impact upon the pit ecosystem function is conitnuously the perch with the dominance of individuals with SL 46 to 337 mm and weight zup to 850 g.

O gerenciamento dos estoques pesqueiros, um dos instrumentos da biomanipulação, deve ter início com a classificação das espécies existentes e sua diversidade, a estrutura da rede alimentar e as relações reguladoras, como a relação predador-presa. O lago Paranoá (Brasília - DF) é um reservatório urbano que sofre pressões antrópicas devido a seus usos múltiplos. Após a construção enchimento, sucessivas introduções de espécies ictíicas exóticas causaram um desequilíbrio que, associado às pressões descritas acima, geraram uma aceleração no processo de eutrofização deste ambiente. Desta forma, os objetivos deste trabalho foram: avaliar os impactos ambientais da introdução das espécies predadoras sobre a cadeia trófica e a qualidade da água do reservatório; determinar a eficiência das diferentes espécies de predadores no controle das presas nas áreas marginais da represa, discutindo possíveis estratégias de manejo pesqueiro baseadas na estocagem de peixes predadores. Para tanto foram construídos 10 limnocurrais com lonas impermeáveis numa baía localizada no ETE-Norte (Estação de tratamento de esgotos - Norte). Em seu interior, após a retirada de todos os peixes, foram estocadas por um período de 28 dias, duas espécies de predadores (Cichla ocellaris e Pseudoplatytoma fasciatum) e uma comunidade simplificada de presas (Tilapia rendalli e Oreochromis niloticus), acima da capacidade do suporte do sistema, definida em 4 classes de tamanho. As biomassas de estocagem foram determinadas a partir da aplicação de retenona em uma área com dimensões conhecidas, e extrapoladas para as áreas dos limnocurrais. As variáveis físicas e químicos da água foram acompanhados semanalmente durante o experimento. Não houve diferenças significativas entre os tratamentos, em relação às variáveis limnológicas. Quanto ao controle das presas, o tucunaré mostrou-se um predador eficiente em relação às classes de tamanhos menores ) (2 - 6,9 cm e 7 - 12,9 cm), fato não observado para o tratamento com surubim. De acordo com os resultados obtidos, não foi comprovada a hipótese de cascata trófica devido à complexidade das interações entre os organismos em ambientes tropicais. / The managing of the fish stocks, one of the tools of the biomanipulation, must begin with the classification of the present species and their diversity, of the structure of the food web and of the regulation relations (as the relation predator-prey).The Paranoá Lake (Brasília, DF) is an urban reservoir that suffers human pressures as a result of its multiple uses. After its construction and filling, the successive introduction of many fish exotic species resulted in an unbalance that, associated with the pressures described above, generated an acceleration in the eutrophication process of the ambient. In this way, the objectives of this work were: evaluate the environmental impacts from the introduction of the species predators in food web and quality from the reservoir\'s water; decide the efficiency of the species of predators in the prey\'s control in the marginal areas from dam, discussing possible fishing strategies of management based in the Stocking of fish predators. Them, 10 limnocorrals were built with waterproof canvases in a bay located in ETE-NORTE (sewers handling Station - North). In its interior, after retreat of all fishes, by a period of 28 days, two species of predators were stocked (Cichla ocellaris and Pseudoplatystoma coruscans), and a community simplified of prey (Tilapia rendalli and Oreochromis niloticus), above from the capacity of the system, defined in 4 classes of size. The biomasses of stocking were determined from application of rotenona in an area with known dimensions, and overstepped for the areas of the limnocorrals. The physical-chemists parameters from the water were accompanied weekly during the experiment. It had no significant differences between the handlings, regarding the variables limnological. As regards the control of prey, C. ocellaris showed itself an efficient predator regarding the smallest classes of sizes (2 - 6,9 cm and 7 - 12,9 cm), fact do not observe for the handling with P. coruscans. Agreement with the results obtained, was not verified to hypothesis of trophic cascade due to the complexity of the interactions between the agencies in tropical environments.

Eutrophication has proven to be a fundamental ecological problem for lakes and other bodies of water all around the world. The process of eutrophication can be defined as a lake containing increasing concentrations of nutrients from external and/or internal input over time. The increase of nutrients in the lake has several consequences for the lake ecosystem, such as the increase in algal blooms (sometimes containing toxic and harmful cyanobacteria) and the decrease of macrophytes. One nutrient that plays a key role in the eutrophication process is phosphorus. To restore eutrophic waters, the external and internal input of phosphorus needs to be reduced. External input can be decreased by reducing the run-off from industrial areas or agriculture. Internal input can be reduced by disrupting the in-lake phosphorus loading processes, which are connected heavily to the lake sediment. The internal phosphorus loading processes can be caused by several different processes. One is the mineralization of organic biomass on the sediment which releases phosphorus into the water, another is the release of previously iron-bound phosphorus from the sediment. Different treatments can be implemented in a lake system to disrupt these internal processes of phosphorus loading and consequently restore the water quality of the lake. Such treatments also influence the biota of the lake and the ecosystem services, because of their effect on water quality. Biomanipulation treatments and aluminum treatments were implemented in lake Växjösjön in Sweden to restore the lake to a more natural and balanced state. Both treatments were effective in reducing the eutrophic conditions of the lake, improving water quality, biota, and the ecosystem services. Local human populations benefit from these improvements, for example by receiving increased revenue from lake recreation. More research is however needed to discern the long-term effects of the treatments in the Växjö municipality, thereby aiding local government and policy makers in their future decisions regarding restoration.