Dissertations / Theses on the topic 'Lakes'

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.

This work explores the fragility of the Great Lakes and the environmental degradation we have caused. My main focus revolves around what the EPA considers to be the Great Lakes Areas of Concern (AOCs). This list contains 27 rivers that flow into the Great Lakes, most of which are or have been areas of industrial and chemical pollution. Through installations involving photography, ceramics, and video, I hope to reveal the issues facing the Great Lakes and explore how people can help.

Approximately 14,500 years ago, Pleistocene Lake Bonneville discharged 4750 km 3 of water over the divide between the closed Bonneville Basin and the watershed of the Snake River. The resulting flood, emanating from the divide at Red Rock Pass, Idaho, followed the present courses of Marsh Creek, the Portneuf River, and the Snake and Columbia Rivers before reaching the Pacific Ocean. For the 1100 kilometers between Red Rock Pass and Lewiston, Idaho, the Bonneville Flood left a spectacular array of flood features that have allowed for geologic reconstruction and quantitative evaluation of many aspects of the flood hydrology, hydraulics, and sediment transport. Geologic evidence of maximum flood stages in conjunction with step-backwater modeling provides for peak discharge estimates and understanding of local hydraulic flow conditions for ten separate reaches along the flood route. Peak discharge was approximately 1.0 million m³•sec⁻¹ at the Lake Bonneville outlet near Red Rock Pass. Downstream, the maximum discharge had attenuated to 0.57-0.62 million m³•sec⁻¹ by arrival at Lewiston. Attenuation was primarily the result of flow storage in the wide alluvial valleys of the western Snake River Plain. The local hydraulic conditions (depth and velocity) of the Bonneville Flood varied significantly within and between the study reaches. The rate of energy expenditure was also highly varied; local calculated stream-power values ranged from less than 10 watts•m² to 100,000 watts•m². Greater than 60% of the total energy loss at peak discharge was expended in a total distance that encompassed less than 10% of the flood route. These spatial variations in local hydraulic conditions were profoundly important in controlling the distribution of flood processes and features. The deposition of tractively-transported cobbles and boulders (measured diameters ranged from less than 10 cm to greater than 10 m) occurred in reaches of decreasing flow energy within quantitatively-definable limits of flow energy. Areas of erosion are more difficult to precisely evaluate; however, they were restricted to reaches of greater stream power. It is likely that cavitation was an important erosional agent in many areas of most intense flow conditions.

The study has attempted to characterise the physicochemical limnology and distribution of algal flora of two salt lake systems in Western Australia, one from the coastal Esperance region and the other from the inland Kambalda region. Climatic conditions, water regimes and physicochemistry were found to differ markedly between the two lake systems and a total of 171 algal taxa, representing five divisions, were recorded. Of these, 82 were members of Bacillariophyta, 48 of Cyanophyta, 33 of Chlorophyta, two of Euglenophyta and six of Dinophyta. The physical limnology of salt lakes in the Esperance region was seasonally variable, defined by climatic conditions. As such, the lakes investigated in the region exhibited a stable cycle of filling during winter and spring, and drying out in summer. Four of the lakes in the region could be classified as near-permanent, and one as seasonal on the basis of predictability and duration of filling. Seasonal fluctuations in water depth resulted in fluctuations in salinity levels. Salinity levels ranged from subsaline to hypersaline, and all the lakes in the region were alkaline. In addition, the lakes were well mixed in terms of oxygen and temperature, and were impacted by eutrophication from their catchments. They were either mesotrophic or eutrophic with respect to both nitrogen and phosphorus. In geological terms, lakes in the Esperance region were separated only recently from the ocean, and two lakes retain a connection with marine waters, one through a creek during years of high rainfall and one through hydrological interactions with groundwater of marine origin. In general, the algal communities of lakes in the Esperance region were similar to those of other Australian coastal salt lakes.Diatoms and cyanobacteria were dominant in all lakes except the most eutrophic, Lake Warden, in which benthic green algae were most abundant. All algal species recorded were known for their wide geographic distribution and their distribution in Australian coastal waters. Characteristically coastal diatom species included Achnanthes brevipes, Achnanthes coarctata, Achnanthes lanceolata var. dubia, Achnanthidium cruciculum, Campylodiscus clypeus, Cyclotella atomus, Cyclotella meneghiniana, Cyclotella striata, Mastogloia elliptica, Mastoglia pumila, Nitzschia punctata and Thalassiosira weissflogii. The inland salt lakes of the Kambalda region form part of an extensive palaeodrainage system, and were much less predictable in terms water regime than lakes in Esperance. Water depth was determined by seasonal variability in rainfall and evaporation, and by summer cyclonic rainfall events that were unreliable from year to year. In addition, rainfall varied spatially within the region. As such, most lakes were classified as intermittent. Two lakes in the region were not classified on the basis of water regime as they were too highly impacted by mining activities including water diversion and impoundment, water extraction and discharge of groundwater. Salinity varied in accordance with drying and filling cycles in the lakes except the most hypersaline as the volume of water received during rainfall events was insufficient to dilute the extensive surface salt crusts they each supported when dry. Salinities recorded in the region ranged from subsaline to hypersaline, and ionic compositions exhibited the same spectrum as seawater.Calcium levels were significantly higher than in lakes from the Esperance region due to weathering of calcium rich sediments, and pH ranged from weakly acidic in the most hypersaline lakes to alkaline in the least saline lakes. All were well mixed in terms of oxygen and temperature. Kambalda salt lakes support distinctive algal communities dominated by diatoms and cyanobacteria that are adapted to intermittent water regimes, extended periods of desiccation and variable salinity. Not surprisingly then, none of the algal taxa recorded from the region were regionally restricted, all noted previously in the literature to have wide geographic distributions, and to be tolerant of a range of physicochemical conditions. Canonical correspondence analysis showed that, of the physicochemical parameters that were investigated in this study, both salinity and pH interacted in determining algal community structure. Both of these attributes were correlated with water depth, which varied according to climatic conditions in a seasonal drying and filling cycle. The general relationship between species richness and pH and salinity, and species diversity and pH and salinity was simple and linear; with increasing pH and salinity, species diversity and species richness decreased. What was less simple, and non-linear, was the nature of the relationship between species richness and diversity and salinity within more narrowly defined ranges of salinity. As salinity increased from <1ppt to 30ppt there was a dramatic reduction in species richness and diversity, then, as salinity increased from 30ppt to 100ppt the rate of decrease slowed. Between 100ppt and 250ppt there was almost no relationship between salinity and species richness and species diversity, but after 250ppt both species diversity and species richness declined markedly.

Mining of lignite in Lusatia has a long history of over 100 years. The extracted brown coal is utilized to generate electricity in three large power plants: Jänschwalde, Boxberg, and Schwarze Pumpe. With an annual carbon dioxide (CO2) output of approximately 50 million tons, these power plants are among Germany’s large-scale CO2 emitters. The environmental impact from open-pit mining is of a considerable degree and currently poses a challenging problem. The groundwater deficit in 1990 was 7 billion m3 over a surface area of approximately 2100 km2 (Luckner, 2006a) and was bisected in value until today. Due to the decline of mining activity and the termination of mine drainage at most open pits in the Lusatian region, the groundwater table has recovered forming 28 pit lakes (Zschiedrich, 2011). The majority of the post mining lakes do not meet the quality standards for pH, iron or sulfate parameters; because of pyrite oxidation that produces acid mine drainage (Luckner, 2006b, Klapper and Schultze, 1995, Schultze et al., 2010). The post mining lakes in Lusatia have low pH values (3 – 4), high sulfate contents (up to 2800 ppm) as well as high iron concentrations (100 – 150 ppm). Lakes are flooded by groundwater and using surface water from Spree and Neisse River to achieve fast filling and dilution; however, due to the limited availability of surface water, further rehabilitation strategies for the region had to be investigated. Between 1970 and 1990, approximately 26 million m3 of suspended fly ash were deposited in the lake Burghammer and settled as an ash body at its base; where it may be used for rehabilitation. In a first experiment conducted in 2001 material from the ash body was picked up and redistributed throughout the lake. By this treatment the pH of the lake was raised temporarily; however, a sustainable remediation was not achieved. Based on these experiments it was investigated whether the ash reacts more sufficiently through additional CO2 injection or not. Aim was to combine the rehabilitation of acid mine lakes with the utilization of atmospheric carbon dioxide emissions from coal-fired power plants. The CO2 sequestration is achieved through the generation and accumulation of carbonates in the lake. The following equations describe the precipitation of carbonate by using CO2 and alkaline earth cations M: CO2 + MO → MCO3 (s) CO2 + M(OH)2 → MCO3 (s) + H2O Therefore, neutral pH conditions are necessary for the long-term accumulation of carbonates in the lakes. In laboratory investigations it was shown, that the 20 to 30 years old fly ash deposits of lake Burghammer can be used for carbonate sequestration and lake water treatment. Bivalent ions (Ca2+, Mg2+) are eluable and available for carbonate precipitation; on average we assumed 1 wt.-% of reactive calcium to be contained in the settled ash sediments. Settled fly ash sediments are less reactive than fresh fly ash from a power plant (e.g. Schwarze Pumpe). During batch experiments, we increased the buffering capacity to maximum values of 7 mmol/L. Beforehand no buffering capacity exists due to the low pH of 2.9 in the lake. Batch investigations provided a sequestration potential of 17 g CO2/kg ash sediment; in comparison fresh fly ash results in a sequestration potential of 33 g CO2/kg ash (Schipek and Merkel, 2008b, Schipek and Merkel, 2008a, Schipek, 2009). Based on the laboratory results a field experiment was conducted. In this field experiment gas injection lances were installed to a sediment depth of 12 m. Gaseous CO2 was applied with a pressure of 2.2 bar and 2.2 m³/h for 3 months and lake water was monitored during injection. Variations in total inorganic carbon due to diffusion processes of CO2 saturated pore waters could be observed. As the pilot experiment comprised only a small area of lake Burghammer no initial neutralisition (e.g. by a suction excavator) was possible. Thus, no further changes in water chemistry were observed. Drilling cores in the vicinity of the injection area provided mineralogical and geochemical conditions before and after CO2 treatment. No trace metal mobilization was found during CO2 injection. Most elements showed decreasing trends or didn’t change significantly. Calculated saturation indices for calcite indicated equilibrium conditions or slightly oversaturated conditions (SICalcite,average +0.12; SICalcite,median +0.31). Geochemical and mineralogical investigations proved that CO2 sequestration is possible with an average precipitation rate of 0.5 wt.-% (2.2 g CO2/kg). The maximum rate for carbonate precipitation was determined with 7.4 wt.-% Calcite, according to 32.6 g CO2 per kilogram treated ash. Besides the use of the settled fly ash as neutralizing agent in acidic mining lakes, laboratory and field investigations were conducted in order to improve in-lake liming. In batch and columns experiments, different liming agents (synthetic marble powder and industrial products) were tested and investigated. Significant differences in reactivity were obvious at pCO2 > 3.8 • 10-4 atm. Ions typical for acid mine drainage (e.g. Mn2+, Cd2+, SO42-) do have different effects on the kinetic of carbonate dissolution. Manganese concentrations typical for acidic mining lakes inhibit calcite dissolution. Cadmium has as well a significant influence on dissolution and kinetics. Only circa 50 % of the calcium concentration was reached with cadmium as inhibitor compared to the dissolution in pure water. Increased CO2 partial pressure might be used to compensate inhibtion by material impurities and/or water constituents. Column experiments showed that a multi-stage application of liming agent increases the efficiency of a lake treatment. The combination of a first application of calcite (up to pH 4.5) and further application of Ca(OH)2 seemed to be the most promising method. This treatment sheme was successfully applied in lake Burghammer from March 2009 – December 2010 (initial neutralisation and 6 follow-up treatments). Finally, it can be concluded, that in lignite mining districts in-lake treatment of acidic mining lakes is a seminal method to handle water quality problems. Using gaseous CO2 in combination with industrial by-products can be accounted as sustainable method for CO2 sequestration and for treatment of AMD. The advantage for mining areas lays in the prevention during treatment of acid mine lakes. Nevertheless, this method presents only a niche solution due to the dependence on alkaline materials, e.g. fly ash. The development of further strategies and optimization during lake water treatment by in-lake liming might improve the effectiveness of the method. Using calcite instead of NaOH or CaO as liming agent will provide advantages in being more economic and ecological (CO2 bilance). In order to enhance efficiency the use of calcite in combination with CO2 can be a worth considering suggesting. If meteorological parameters (wind) and lake specific characteristics (morphology, currents, etc.) will be considered efforts and costs for in-lake liming will be minimized
Der Abbau von Braunkohle im Lausitzer Bergbaurevier hat seit über 100 Jahren Tradition. Die abgebaute Braunkohle wird dabei hauptsächliche zur Energieerzeugung in den drei großen Kraftwerken Jänschwalde, Boxberg und Schwarze Pumpe genutzt. Mit einem jährlichen Kohlenstoffdioxid (CO2) – Ausstoß von circa 50 Millionen Tonnen gehören diese Kraftwerke zu Deutschlands größten CO2-Emittenten. Der Einfluss auf die Umwelt durch Tagebau-Betrieb ist von beträchtlichem Ausmaß und bringt große Probleme mit sich. Im Jahr 1990 betrug das Grundwasser-Defizit im Lausitzer Bergbaurevier 7 Milliarden m³ auf einer Fläche von circa 2100 km² (Luckner, 2006a). Dieses Defizit hat sich bis zum heutigen Zeitpunkt halbiert. Durch den Rückgang der Bergbauaktivitäten und die Beendigung der Wasserhaltungsmaßnahmen in den meisten Tagebauen, hat der ansteigende Grundwasserspiegel 28 Tagebaufolgeseen geschaffen (Zschiedrich, 2011). Der überwiegende Teil der Tagebaufolgeseen ist aufgrund der Pyritoxidation, welche AMD (acid mine drainage) produziert, hinsichtlich der Wasserqualitätsparameter stark beeinflusst (Luckner, 2006b, Klapper and Schultze, 1995, Schultze et al., 2010). Die Tagebaufolgeseen im Lausitzer Bergbaurevier sind durch niedrige pH-Werte (3 – 4), hoche Sulfat-Konzentrationen (bis zu 2800 ppm) und hohe Eisengehalte (100 – 150 ppm) gekennzeichnet. Die entstehenden Seen sind hauptsächlich durch aufsteigendes Grundwasser und Oberflächenwasser aus den Flüssen Spree und Neisse geflutet. Aufgrund der geringen Verfügbarkeit von Oberflächenwasser mussten weitere Sanierungsmaßnahmen für die Region untersucht werden. Zwischen 1970 und 1990 wurden im Tagebaufolgesee Burghammer circa 26 Millionen m³ Flugasche-Suspension als Aschekörper abgelagert, wobei eine Nutzung zu Sanierungszwecken angedacht war. Im Rahmen einer Aschesedimentumlagerung im Jahr 2001 wurde der pH-Wert des Seewassers kurzzeitig angehoben, eine nachhaltige Sanierung fand jedoch nicht statt. Auf Grundlage dieser Ergebnisse wurde im Rahmen dieser Dissertation untersucht, ob die abgelagerten Aschesedimente nachhaltiger durch Einsatz von CO2 reagieren. Ziel war es die Sanierung von Tagebaufolgeseen mit der Reduktion von CO2-Emissionen aus Kohlekraftwerken zu kombinieren. Diese CO2-Sequestrierung sollte durch die Bildung und Ablagerung von Carbonaten im Seesediment erfolgen. Die Gleichungen (1) und (2) beschreiben dabei die Fällungsreaktion von Carbonaten aus CO2 mit dem Alkalimetall M (aus Oxiden bzw. Hydroxiden): CO2 + MO → MCO3 (s) CO2 + M(OH)2 → MCO3 (s) + H2O Zur Carbonatfällung und nachhaltigen Ablagerung sind neutrale pH-Bedingungen notwendig. In Laboruntersuchungen konnte gezeigt werden, dass die 20 bis 30 Jahre alten Flugaschesedimente zur CO2-Sequestrierung in Kombination mit Seewasserbehandlung genutzt werden können. Zweiwertige Ionen (Ca2+, Mg2+) sind aus den Aschesedimenten eluierbar und stehen für die Fällungsreaktion zur Verfügung. Durchschnittlich 1 Masse-% reaktives Calcium befindet sich in den Sedimenten. Die abgelagerten Aschesedimente sind dabei weniger reaktiv als frische Flugaschen aus Kohlekraftwerken (z.B. Schwarze Pumpe). In Batch-Versuchen mit Tagebaufolgesee-Wasser konnte die Säure-Pufferkapazität auf maximal 7 mmol/L erhöht werden. Sequestrierungs-Raten von 17 g CO2/kg Aschesediment wurden im Rahmen der Versuche erreicht. Im Vergleich dazu betrugen die Sequestrierungs-Raten in Versuchen mit frischen Flugaschen bis 33 g CO2/kg Asche (Schipek and Merkel, 2008b, Schipek and Merkel, 2008a, Schipek, 2009). Auf Grundlage dieser Laborergebnisse wurde ein Feldversuch im Tagebaufolgesee Burghammer geplant. Während diesem wurden Gasinjektionslanzen bis in eine Sedimenttiefe von 12 m im abgelagerten Aschesediment installiert. Gasförmiges CO2 wurde mit einem durchschnittlichen Druck von 2.2 bar und 2.2 m³/h für eine Dauer von 3 Monaten injiziert. Während dieser Zeit fand ein kontinuierliches Monitoring des Seewassers im Bereich der Injektion statt. Veränderungen des Gehaltes an TIC (total inorganic carbon) aufgrund von Diffusionprozessen von CO2-gesättigtem Porenwasser aus dem Aschekörper waren beobachtbar. Da der Feldversuch nur in einem begrenzten Bereich des Tagebaufolgesees Burghammer stattfand und keine Initialneutralisierung vorsah, konnten keine weiteren, großmaßstäblichen Veränderungen im Wasserkörper festgestellt werden. Bohrkernentnahmen im Umfeld des Behandlungsgebietes lieferten Aussagen bezüglich der mineralogischen und geochemischen Beschaffenheit vor und nach CO2-Injektion. Im Porenwasser wurde keine Spurenmetall-(re)-mobilisierung durch die Behandlung mit CO2 festgestellt. Nahezu alle Elemente zeigten einen abnehmenden Trend durch die Behandlung mit CO2, bzw. keine signifikanten Veränderungen. Modellierte Sättigungsindizes für Calcit wiesen auf Gleichgewichtsbedingungen oder leichte Übersättigung bzgl. Calcit hin (SICalcit, Mittelwert +0.12; SICalcit, Median +0.31). Geochemische und mineralogische Untersuchungen zeigten, daß CO2-Sequestrierung mit einer durchschnittlichen Fällungsrate von 0.5 Masse-% (2.2 g CO2/kg Aschesediment) erreicht wurde. Die maximale Fällungsrate wurde mit 7.4 Masse-% Calcit bestimmt, dies entspricht einer Festlegung von 32.6 g CO2/ kg Aschesediment. Neben der Nutzung der abgelagerten Aschesedimente zur Behandlung des Tagebaufolgeseewassers wurden desweiteren Labor- und Feldversuche durchgeführt um In-Lake-Behandlungen mit industriellen Kalkprodukten zu optimieren. In Batch- und Säulenversuchen wurden verschiedene Kalkprodukte (synthetisches Marmorpulver und industrielle Produkte) getestet und untersucht. Signifikante Unterschiede auf die Reaktivität wurde bei erhöhten CO2-Partialdrücken (pCO2 > 3.8 • 10-4 bar) beobachtet. Wasserinhaltsstoffe, die typisch für AMD sind (z.B.. Mn2+, Cd2+, SO42-) zeigten einen signifikanten Einfluss auf die Calcit-Lösungskinetik. Mangankonzentrationen, wie sie in Lausitzer Tagebaufolgeseen vorkommen, zeigten – ebenso wie Cadmium - eine inhibitierende Wirkung auf die Kinetik. Im Vergleich zu Versuchen mit destilliertem Wasser wurden nur ungefähr 50 % der Calcium-Gleichgewichtskonzentration mit Cadmium als Inhibitor erreicht. Erhöhte CO2-Partialdrücke könnten genutzt werden, um die inhibitierende Wirkung von vorhanden Materialverunreinigungen und/oder Wasserinhaltsstoffen zu kompensieren. Säulenversuche zeigten, dass der mehrstufige Einsatz von Kalkprodukten die Effizienz während einer Seewasserbehandlung erhöht. Die Kombination einer Erstbehandlung mit Kalksteinmehl (bis pH 4.5), und einer Behandlungsfortsetzung mit Ca(OH)2 erwies sich als wirkungsvollste Methode. Dieses Behandlungsschema (Initialneutralisation, 6 Nachfolgebehandlungen) wurde im Tagebaufolgesee Burghammer von März 2009 – Dezember 2010 erfolgreich angewandt. Zusammenfassend lässt sich sagen, dass in ehemaligen Bergbaurevieren die In-Lake-Behandlung von Tagebaufolgeseen eine zukunftsträchtige Methode zur Behandlung von Wasserqualitätsproblemen darstellt. Die Nutzung von gasförmigen CO2 in Kombination mit industriellen „Abfall-Produkten“ kann als nachhaltige Methode zur CO2-Sequestrierung und zur Behandlung von AMD bezeichnet werden. Der Vorteil in Bergbaurevieren liegt dabei in der Vorbeugung der Entstehung von Wasserqualitätsproblemen. Dennoch stellt diese Methode nur eine Nischenlösung aufgrund der Verfügbarkeit der alkalischen Materialien (Flugasche) dar. Die Entwicklung und Optimierung weiterführender Strategien zur In-Lake-Behandlung durch Kalkung wird zur Effizienzerhöhung beitragen. Die Nutzung von Kalksteinmehl anstelle von NaOH bzw. CaO als Neutralisationsprodukt wird Vorteile hinsichtlich ökonomischer und ökologischer Sicht (CO2-Bilanz) mit sich führen. Um die Effizienz beim Einsatz von Kalksteinmehl zu steigern, kann der Einsatz von CO2 in Betracht gezogen werden. Sobald meteorologische Parameter (Wind) und see-spezifische Merkmale (Morphologie, Strömungen, etc.) berücksichtigt werden, kann der Aufwand und die Kosten für In-Lake-Behandlungen minimiert werden

Aerobic methanotrophs (MOB) are a functional group of proteobacteria that use methane as their only energy and carbon source. Phylogenetically, such methanotrophs are affiliated with present alpha and gamma proteobacteria. Methanotrophic microorganisms play an essential role in the methane cycle, since they to a great extent reduce potential methane emissions to the atmosphere. In stratified lakes the aerobic methanotrophs are commonly present at the oxic-anoxic interfaces. This study aims to identify the environmental factors that could regulate the distribution of aerobic methanotrophs in the water column of freshwater lakes as well to assess whether a vertical community structure exists there. Lakes Erken and Tämnaren located in central Swedenwere studied using molecular analysis and environmental data. Aerobic methanotrophs were detected throughout the water column of Lake Erken. Two types of methanotroph communities were identified, with distribution patterns that appeared to be correlated to levels of methane in the water. Furthermore one of these communities feature changes in the relative abundance of its member populations along a depth gradient suggesting further differentiation along chemical gradients in the hypolimnion. Sequencing of pmoA amplicons revealed only members of the gamma proteobacteria methanotrophs. Also two novel operational taxonomic units were identified. Methanotrophs communities between Tämnaren and Erken also differ. Together these results indicate the existence of distribution patterns in methanotroph freshwater communities.

Fischgemeinschaften in Seen sind zunehmenden Umweltveränderungen unterworfen. Die Analyse des Einflusses abiotischer und biotischer Faktoren auf die Größenstruktur von Fischgemeinschaften ist entscheidend, um die Entwicklung von Seeökosystemen im Zuge von Umweltveränderungen vorhersagen zu können. Es ist jedoch schwierig Fische in Seen zu beproben, da Fanggeräte selektiv sind. Die Qualität und Vergleichbarkeit von Fischfängen durch Angler, Kiemennetze, Schleppnetze und Hydroakustik wurden untersucht. Anglerfänge eignen sich begrenzt für vergleichende Fischbestandsuntersuchungen. Vertikale Hydroakustik eignet sich für die Fischbiomassequantifizierung in geschichteten Seen. Der Beprobungsaufwand von Kiemennetzen kann reduziert werden, wenn zeitnah hydroakustische Untersuchungen statt finden. Schleppnetze eignen sich für die Beprobung von pelagischen Fischen in tiefen Seen. Die Größenstruktur von Fischgemeinschaften unterschied sich auf regionaler und überregionaler Ebene entlang abiotischer und biotischer Gradienten. Die regionale Studie zeigte, dass tiefe nährstoffarme Seen mit hohen Raubfischabundanzen durch mehr große Fische gekennzeichnet waren. Nährstoffreiche Flachseen mit wenigen Raubfischen zeigten höhere Anteile von mittleren Fischgrößen. Im überregionalen Vergleich führten Temperaturpräferenzen der Fischarten zu zwei Fischgemeinschaften, die sich in ihrer Größenzusammensetzung unterschieden. Ein hoher Anteil großer Salmoniden war typisch für hochgelegene Kaltwasserseen im Norden und Süden Europas. Flachlandseen mit Kühl- und Warmwasserfischen zeichneten sich durch eine Dominanz von kleinen Fischen aus. Das lässt vermuten, dass Fischgemeinschaften in Flachlandseen relativ robust gegenüber Umweltveränderungen reagieren. Kaltwasserfischgemeinschaften könnten im Zuge der Klimaerwärmung starken Änderungen unterliegen, da eine Veränderung in der Artenzusammensetzung von einer Verschiebung in der Größenstruktur hin zu mehr kleinen Fischen begleitet sein wird.
Lake fish assemblages are increasingly exposed to environmental change in their habitats. The investigation of abiotic and biotic factors and their effects on the size structure of lake fish is essential for predicting the response of fish assemblages to environmental change. However, sampling of lake fish is challenging because sampling gears are selective. The quality and correspondence of fish catches from angling, gillnetting, trawling and hydroacoustics were analysed. Non-standardised catch data from recreational angling were of limited quality for a comparison of fish stocks. Vertical hydroacoustics is an efficient method to quantify fish biomass in stratified lakes. Sampling effort of multi-mesh gillnets can be reduced when fish abundance estimates are derived from contemporarily operating hydroacoustics. Trawling is useful to sample pelagic fish assemblages in deep lakes. The size structures of fish assemblages differed on a small and a large geographical scale along gradients of abiotic and biotic lake descriptors and differences in fish assemblage composition. At a small geographical scale assemblages in deep and less nutrient-rich lakes with high predator abundances were characterised by a higher proportion of large fish. Shallow nutrient-rich lakes with few predators were characterised by more medium-sized fish. At a large geographical scale thermal optima of fish generated two types of assemblages with different size structures. A high proportion of large salmonids was observed in coldwater lakes at high elevation sites in northern and southern Europe. Lowland lakes with cool- and warmwater fish were dominated by small-sized individuals. The results suggest that lowland lake fish assemblages are relatively robust against environmental change. Coldwater fish assemblages instead may suffer dramatic consequences from global warming as expected species shifts are likely to be accompanied by shifts in the size structure towards smaller individuals.

Abstract. This thesis reviews studies about the lakes and seas of Saturn’s moon, Titan. Conditions on Titan’s surface are first estimated to validate that substances in Titan’s atmosphere can exist in liquid phase. This is followed by descriptions of devices that have been used to study Titan from Earth, space and on its surface. Research concerning the detection and distribution of the lakes are then discussed. Features of the lakes such as surface areas, chemical compositions and formations like shores are looked into. Results from models that describe liquid currents driven by tidal forces, wind, temperature differences and rain induced density differences are given. This leads into discussion of liquid surface waves. Titan’s potential for supporting life is also considered. Observation of a disappearing and reappearing region in Titan’s sea, the Magic Island phenomenon, is construed and possible causes for this phenomenon are examined. Lastly, future mission projects that are capable of studying the lakes in situ are described with the emphasis on the Titan Submarine project.

Nonylphenol is a widely used organic compound which has been reported to have potential risk to aquatic environment. According to the result of recent studies, it has been detected in many lakes in Stockholm, Sweden, which raised great concern. In this thesis, a dynamic fate model was adopted and modified from literature in order to study the distribution and concentration of nonylphenol in small lakes, guide the field sampling and provide information for corresponding decision making. Two lakes in Stockholm, Lake Trekanten and Lake Drevviken, were selected as case studies. Another model was included for comparison purpose. Based on the model result, the most important nonylphenol removal process in both lakes was the transformation in water. A sensitivity analysis showed that the model results were most sensitive to the process of nonylphenol water inflow. In terms of sediment concentration of nonylphenol, satisfactory agreements were obtained from the comparison between model results and field data. However, problems, such as the simultaneous handling of nonylphenol and nonylphenol ethoxylates, may cause uncertainties on the model performance. The result of the analysis about scenario load change and the seasonal variation showed that the sediment nonylphenol content is more stable to the seasonal change compare to nonylphenol water content, but the response times to load change of nonylphenol content in these two compartments are quite close and somewhat lower than the water residence time.

The Rotoroa Complex located in NW Nelson, represents a remnant plutonic fragment of an extensive subduction system active between 140-130 Ma. The arc system has been subject to large scale transcurrent faulting during the Early Cretaceous. The result is a series of "dismembered Mesozoic volcanic and plutonic arc associations that are sandwiched between terranes of the Western and Eastern Provinces" (Kimbrough et al 1993). This association is collectively described as the Median Tectonic Zone (MTZ) by Bradshaw (1993), and Kimbrough et al (1993). The rocks encompassed by the term Rotoroa Complex range from rare hornblendite through gabbro to diorite and quartz diorite, all typically rich in hornblende. The complex has been metamorphosed in part by the Early Cretaceous emplacement of the Separation Point Batholith, resulting in widespread felsic sheets and dikes of Separation Point Suite affinity being present throughout the Rotoroa Complex. Lamprophyre camptonite dikes of unknown age are also intruded throughout the complex, which has been subjected to brittle deformation due to movements on the Alpine Fault since Late Oligocene - Early Miocene times. The Rotoroa Complex is broadly metaluminous, calc-alkaline, medium to high K in nature, and has island-arc subduction-related geochemical characteristics. The geochemical variation reflects primary igneous fractionation processes. The Rotoroa Complex probably correlates with the Darran Complex of Fiordland, based on similarities in rock type, geochemistry, structural position and magnetic anomalies. The geochemical trends obtained from analyses of the Rotoroa Complex are sufficiently similar to those described in the Darran Complex to support this notion.

Coastal and shallow lakes are often subjected to eutrophication due to nutrients from catchment farming activities. Lake Ellesmere (Te Waihora) is a hyper-eutrophic lake which has gained recent attention because of concerns over its ecological health and fishery status. This study investigated the benthic ecology of the lake by extensive spatial and temporal sampling. Eight littoral sites were sampled on a single occasion, and 20 benthic sites were sampled once per season for one year. Water chemistry conditions, substrate and invertebrate communities varied significantly around the lake. Salinity, pH, DO and seston were primarily affected by freshwater inputs from inflow streams and salt water intrusion due to the lake opening to the sea. On these occasions, salinity reached 32 ‰ at the lake outlet. The lake invertebrate community was depauperate, comprising of only two species of invertebrate predators restricted to the littoral zone and eight benthic invertebrate taxa, dominated by oligochaetes, amphipods and chironomids. Benthic invertebrate abundances also reflect the dominant local substrate, where oligochaetes and chironomids preferred areas of silt substrate, whereas Potamopyrgus preferred harder substrate. Stable isotope and gut analysis determined that the primary food sources within the lake were phytoplankton and algae. Macrophytes provided a minimal contribution to the food web, possibly relating to the change in status from a clear water, macrophyte dominated lake to a turbid, phytoplankton dominated condition since the Wahine Storm in 1968. Isotope analysis also showed that the lake food web was markedly different in its carbon values from food webs of its inflow streams and nearby marine source. However the lake food web did show a marine-derived carbon signature. A mesocosm experiment testing the effect of common lentic predators on the abundance of the lake chironomid Chironomus zealandicus, showed that if invertebrate predators were present in the lake they could markedly reduce the abundance of the pest prey species. This study highlights that the frequent re-suspension of bottom sediments, lake level fluctuation resulting in wetting and drying of littoral zones, and the management of the lake opening to the sea all have an effect on the benthic ecology of Te Waihora.

Lake restoration and management strategies focus on reducing the negative impacts of enriched or polluted inflows. These strategies become of paramount importance when lakes are used for recreational and/or drinking water purposes. Long term control of eutrophication and turbidity problems associated with large inflow loads is usually oriented to catchment management. Although it has been suggested that this is the correct long term approach, public concerns usually require a short term solution. In addition, due to political and economic costs related to changes in catchment management, in-lake restoration technologies have been emerging as a viable pretreatment option, complementary to water treatment plants, both reducing the operational costs of the water treatment plant and ameliorating the water residing in the lakes. This research investigates the effects of two in-lake technologies on the dynamics of inflowing rivers, where basin shape plays a significant role. The three lakes in this study suffer from eutrophication combined with a distinctive water quality problem: from turbidity in Silvan Reservoir (Australia), to heavy metal loads in Coeur d'Alene Lake (USA) and industrial wastes in Lake Como (Italy). Firstly, the influence of basin morphology, wind speed, and wind direction on the fate and transport of two rivers flowing into the L-shaped Coeur d'Alene Lake was examined, and it was shown that transport and mixing patterns in a lake can be greatly influenced by the shape of the lake, leading to important consequences for the plankton ecology in the lake. Secondly, in Silvan Reservoir we investigated the potential to modify the basin shape using vertical barriers, increasing the retention time and hence the barrier capacity to microbial pollution. A final in-lake technology was tested for Lake Como, using a downward pointing impeller to remove polluted water from the coastal margin. Lessons from these three examples indicate that there is significant potential for in-lake remediation at relatively low cost, over relatively short timescales.

We present two novel stable isotope methods for measuring lake metabolism and compare the results to traditional techniques. The delta 18O method measures planktonic gross primary production (GPP) from dissolved oxygen concentrations, isotopes and respiration (R) and the delta 13C method measures "whole-lake" GPP and R from dissolved oxygen and carbon concentrations and isotopes. All three methods showed GPP was greater than R over the ice-free season and estimates of GPP were not significantly different. There was also no significant difference in R as measured by bottle incubations and the delta13C method. However, the delta 13C method does not account for inputs of external carbon which will result in underestimation of R and overestimation of GPP. In systems with significant allochthonous carbon inputs, the delta13C method cannot be accurate unless these inputs are accounted for. The delta18O method was used to measure metabolic parameters of twenty-one northern temperate lakes and showed GPP dominated over R during the ice-free season. GPP and R were most strongly correlated with lake temperature, which in turn is a function of the amount of solar radiation received by the lake. Our results imply that it is this solar radiation that drives planktonic gross primary productivity, which in turn drives the majority of planktonic respiration. Variation in dissolved organic carbon only explained 8% of the variation in planktonic R, while variation in planktonic GPP explained approximately 80% of the variation in planktonic R. Despite general autotrophy in the lakes, they were generally oversaturated in CO2 during the ice-free season, on average 252+/-25%. However, we found little evidence to conclude that this was the result of an excess of in situ respiration over production. The magnitude of the annual excess of R over GPP was not sufficient to account for the flux to the atmosphere. Moreover, carbon evasion was not a function of respiratory flux, nor did the isotopic signature of dissolved CO2 in the lakes present evidence of respiration. Groundwater inputs of carbon dioxide represent a plausible source for carbon dioxide oversaturation in some but not all of the lakes sampled.

Two large, nationwide monitoring data sets were compiled and statistically treated in order to create a national picture of the problems with high contents of mercury (Hg) and radiocesium (137Cs) in fish. Beside these two data sets, 75 lakes in four counties (Västernorrland, Gävleborg, Örebro and Kronoberg) were studied in connection to an evaluation of different measures to decrease the content of Hg and 137Cs in fish. An important objective was to investigate and determine the relationship between the content in fish and the load of the elements and how this relationship was affected by different abiotic lake characteristics. Several alternatives to measure the lake doses of Hg and 137Cs were evaluated (concentration in different fractions in lake water, in settling particles, and in surface sediments). About 10000 Swedish lakes were calculated to have a mean Hg content in 1-kg pike (FHg) above 1 mg kg-1 (wet weight) in the end of 1980’s, that is a 5-fold increase compared to the calculated preindustrial mean value. The cumulated domestic Hg- sources of emission make the largest contribution to the presently high mercury levels in pike and particularly so in central and northern Sweden.The second most important cause is acidification and thirdly Hg emissions from European sources. The content of 137Cs in fish normalized to 100 g perch (FCs) was above the limit for commercial sale, 1500 Bq kg-k in about 14000 Swedish lakes during autumn of 1987. An empirical model including Chernobyl fallout, hydraulic residence time and ionic strength explained almost 60 % of the inter-lake variation in FCs. At the same level of fallout, this difference in lake sensitivity, gave a tenfold difference in the initial transfer from fallout to small perch. A significant relationship was demonstrated between the lake dose of 137Cs and the content in fish. No such clear relationship existed for Hg due to the much more complex chemical and biological behaviour of Hg, where especially factors affecting méhylation and food web structure seems crucial. Lakes with a low relative sedimentation of Hg did also have a low relative sedimentation of 137Cs due to differences in particle sedimentation rates between the lakes. The sedimentation rate of radiocesium was well correlated to the natural concentration of major base cations and intercorrelated parameters such as pH, alkalinity and conductivity. The higher scavenging capacity in lakes with higher concentration of major base cations was due to higher particle sedimentation rates and higher K<i values in these lakes. However, the water chemistry was probably not causal in this respect, despite the high correlation, the distribution and sedimentation coefficients for radiocesium was not notably affected of the increased mean concentration of major base cations after liming and potash addition. It is suggested that a likely causal factor rather would be the amount and nature of scavenging agents (possibly clay minerals), which in these lakes was indicated by the natural concentration of base cations in the water. In general, the remedial measures gave the intended water chemical response with substantially increased mean values of alkalinity, hardness and pH. Two years after the start of the remedies, the Hg concentration in small perch (Hg-pe) was reduced by about 30% on average. The sedimentation rate of Hg decreased during 1988 and 1989 (i.e. after remedial measures) in contrast to the mean concentration of total Hg in water, thus, the retention decreased. None of the methods applied gave any rapid and clear reduction in the concentrations of 137Cs in fish, in comparison with lakes where the water chemical or biological conditions not were changed.

Diss. (sammanfattning) Umeå : Umeå universitet, 1993,, härtill 6 uppsatser.

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One of the practices for dealing with water pollution from point and non point pollution sources is the use of on-line purification lakes. The Lea Marston lakes were built in the early 1980' s to reduce the pollution load transported by the River Tame to the River Trent. The lakes operate on the principle of particle bound contaminant sedimentation. The lakes were observed to be efficient at reducing suppressed (ATU) biochemical oxygen demand (BOD(ATU)), suspended solids (SS) and metals under dry weather flow and wet weather flow conditions. However, ammoniacal-nitrogen (ammonia) is observed to increase across Lake 1. The dominant mechanism of removal is via sedimentation with greater removal occurring under higher inlet concentrations. The addition of ammonia occurs possibly via diffusion with the bed sediments providing a source of ammonia. The bed sediments were identified as a potential pollution source and processes such as diffusion and resuspension could adversely affect the water quality across Lake 1. Porewater and surface water profiles identify the significance of the bed sediments as a sink for dissolved oxygen and a source of ammonia. A modelling study showed that a River Quality Objective (RQO) of River Ecosystem Class (RE) 2 could be achieved at the lakes inlet by improvements in nearby wastewater treatment works effluent quality and water quality from the upper catchment. However, the outlet water quality would probably be adversely influenced by ammonia released from the lake sediments.

A combination of geological, geographical and climatic conditions; favour the evolution of stable alkaline environments, such as the soda lakes of East African Rift Valley. These lakes are often saline as well as alkaline. Soda lakes are potentially the best sources of alkaliphilic microoganisms, but they are virtually unexplored. The few studies done indicate that soda lakes have very high primary productivity, due to the dense population of phototrophic microorganisms, either cyanobacteria or phototrophic eubacteria or both. Soda lakes are therefore, likely to support a large population of organotrophic bacteria. A quantative study of major nutrients, cyanobacteria and organotrophic bacteria was undertaken from Oct. 1988 to Sept 1989 on Lakes Bogorla, Elmenteita, Nakuru and to a lesser extent Lake Magadi. The cyanobacteria, especially Spirulina platensis were the major primary producers in the less saline lakes (Bogorla, Nakuru and Elmenteita), while the photosynthetic bacteria probably Ectothiorhodospira are the major primary producers in the more saline Lake Magadi. The algal population was significantly limited by phosphate, nitrogen and conductivity levels. The population of alkaliphilic organotrophic bacteria in the Kenyan soda lakes was 10s CFU/ml (viable count) and total bacterial count of l0'.;-l0'.;bacteria/ml. The organotrophic bacterial populationwas also limited by total phosphate, total nitrogen and conductivity levels, and was determined more by the water chemistry than by organic carbon availability. Majority of the aerobic organotrophic bacteria were Gram-negative comprising of six distinct clusters when analysed using the procedures of numerical taxonomy. These Gram-negative alkaliphilic bacteria formed clusters distinct from any of the known gram-negative bacteria tested and are likely to be totally new organisms. Chemotaxonomic studies showed that these organisms possesed ubiquinones with 7 or 8 isoprene units, and the polar lipids lacked glycolipids but had large amounts of phosphclipids. The % mol G+C of the gram-negative alkaliphiles ranged from 53.1 to 65.0 (Tm). Organisms in the same cluster group were related at 60% homology by DNA-DNA hybridization; indicating that the majority of the Gram-negatives may belong to a large supraspecific grouping. The few Gram-positive isolates formed less distinct clusters, and two Gram-positive isolates N12 and N16 formed spores and closely resembled isolates WN11 and WN13 (Weisser & Truper, 1985) from Wadi Natrun which have been positively identified as Bacillus spp. Arcbaeobacteria were not isolated Lakes Bogoria, Elmenteita and Nakuru. In the more saline Lake Magadi, eubacterial haloalkaliphlies dominated at low conductivity and archaeobacterial haloalkaliphiles dominated at high conductivity. A new haloalkaliphilic archaeobacterium which has rod-shaped, gas-vacuolated cells and different polar lipid patterns from the 3 Natronobacterium species already described (Ross, et al, 1985) was isolated from Lake Magadi. A new species, 'Natronobacterium vacuolata' is proposed. A coccoid Gram-positive organism, MU5 was also isolated from Lake Magadi, and resembled the type species in the genus Natronococcus. However, polar lipid patterns and SDS-PAGE gels show that MU5 is not identical to SP4.

Zooplankton diel vertical migration (DVM) plays a pivotal role in controlling trophic interactions and nutrient transport in lakes and oceans. Understanding behaviours and responses of diel migrators is therefore essential to knowledge of physical processes and ecosystem functioning. This thesis investigated zooplankton hydrodynamics during the DVM in freshwater bodies through two different research topics. The first research explored the potential of swimming zooplankton hydrodynamics in affecting lake turbulent and biological processes. Past research suggests that zooplankton may be able to inject turbulent kinetic energy (TKE) in the water column when organisms swim. This process, referred to as biomixing, may increase vertical mixing in lakes. Since no field studies exist about biomixing by small zooplankton, turbulence and mixing were sampled in a lake during the dusk DVM of Daphnia. Results indicate that swimming Daphnia did not intensify dissipation rates of TKE and vertical fluxes. This suggests that small zooplankton cannot affect lake mixing even when organisms collectively swim. The second research examined how changes in ecosystem conditions affect zooplankton displacement velocity (DV) during the DVM of Daphnia. Currently, it is not known which environmental factors are key in driving this velocity. DV was measured in the field during the sunset migration (upwards DV) and sunrise migration (downwards DV) along with temperature, relative change in light intensity, chlorophyll-a and zooplankton concentration, as possible velocity drivers. Results show that upwards velocities were strongly correlated with the water temperature in the migrating layer, suggesting that temperature can control swimming activity, metabolic rates and escape reactions from predators. Downwards velocities were instead constant. Modelling this velocity as a sinking rate indicates that buoyancy and gravity are the governing parameters. The model also suggests that zooplankton favour passive sinking over active swimming to preserve energy and generate hydrodynamic disturbances not detectable by predators.

The study has attempted to characterise the physicochemical limnology and distribution of algal flora of two salt lake systems in Western Australia, one from the coastal Esperance region and the other from the inland Kambalda region. Climatic conditions, water regimes and physicochemistry were found to differ markedly between the two lake systems and a total of 171 algal taxa, representing five divisions, were recorded. Of these, 82 were members of Bacillariophyta, 48 of Cyanophyta, 33 of Chlorophyta, two of Euglenophyta and six of Dinophyta. The physical limnology of salt lakes in the Esperance region was seasonally variable, defined by climatic conditions. As such, the lakes investigated in the region exhibited a stable cycle of filling during winter and spring, and drying out in summer. Four of the lakes in the region could be classified as near-permanent, and one as seasonal on the basis of predictability and duration of filling. Seasonal fluctuations in water depth resulted in fluctuations in salinity levels. Salinity levels ranged from subsaline to hypersaline, and all the lakes in the region were alkaline. In addition, the lakes were well mixed in terms of oxygen and temperature, and were impacted by eutrophication from their catchments. They were either mesotrophic or eutrophic with respect to both nitrogen and phosphorus. In geological terms, lakes in the Esperance region were separated only recently from the ocean, and two lakes retain a connection with marine waters, one through a creek during years of high rainfall and one through hydrological interactions with groundwater of marine origin. In general, the algal communities of lakes in the Esperance region were similar to those of other Australian coastal salt lakes.
Diatoms and cyanobacteria were dominant in all lakes except the most eutrophic, Lake Warden, in which benthic green algae were most abundant. All algal species recorded were known for their wide geographic distribution and their distribution in Australian coastal waters. Characteristically coastal diatom species included Achnanthes brevipes, Achnanthes coarctata, Achnanthes lanceolata var. dubia, Achnanthidium cruciculum, Campylodiscus clypeus, Cyclotella atomus, Cyclotella meneghiniana, Cyclotella striata, Mastogloia elliptica, Mastoglia pumila, Nitzschia punctata and Thalassiosira weissflogii. The inland salt lakes of the Kambalda region form part of an extensive palaeodrainage system, and were much less predictable in terms water regime than lakes in Esperance. Water depth was determined by seasonal variability in rainfall and evaporation, and by summer cyclonic rainfall events that were unreliable from year to year. In addition, rainfall varied spatially within the region. As such, most lakes were classified as intermittent. Two lakes in the region were not classified on the basis of water regime as they were too highly impacted by mining activities including water diversion and impoundment, water extraction and discharge of groundwater. Salinity varied in accordance with drying and filling cycles in the lakes except the most hypersaline as the volume of water received during rainfall events was insufficient to dilute the extensive surface salt crusts they each supported when dry. Salinities recorded in the region ranged from subsaline to hypersaline, and ionic compositions exhibited the same spectrum as seawater.
Calcium levels were significantly higher than in lakes from the Esperance region due to weathering of calcium rich sediments, and pH ranged from weakly acidic in the most hypersaline lakes to alkaline in the least saline lakes. All were well mixed in terms of oxygen and temperature. Kambalda salt lakes support distinctive algal communities dominated by diatoms and cyanobacteria that are adapted to intermittent water regimes, extended periods of desiccation and variable salinity. Not surprisingly then, none of the algal taxa recorded from the region were regionally restricted, all noted previously in the literature to have wide geographic distributions, and to be tolerant of a range of physicochemical conditions. Canonical correspondence analysis showed that, of the physicochemical parameters that were investigated in this study, both salinity and pH interacted in determining algal community structure. Both of these attributes were correlated with water depth, which varied according to climatic conditions in a seasonal drying and filling cycle. The general relationship between species richness and pH and salinity, and species diversity and pH and salinity was simple and linear; with increasing pH and salinity, species diversity and species richness decreased. What was less simple, and non-linear, was the nature of the relationship between species richness and diversity and salinity within more narrowly defined ranges of salinity. As salinity increased from <1ppt to 30ppt there was a dramatic reduction in species richness and diversity, then, as salinity increased from 30ppt to 100ppt the rate of decrease slowed. Between 100ppt and 250ppt there was almost no relationship between salinity and species richness and species diversity, but after 250ppt both species diversity and species richness declined markedly.

Thesis (Ph.D.)--University of Missouri-Columbia, 2006.
The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file viewed on (March 1, 2007) Vita. Includes bibliographical references.

This thesis presents temporal perspectives of lake acidification in Sweden. Sediment records have been used to study timing, trends and causes of acidification, and two different techniques for assessing past lake-water acidity are presented. A new technique for pH prediction, based on near-infrared (NIR) spectroscopy of surface sediments, is developed. This study shows that there is a pH related fraction of lake sediments that can be recorded by NIR analysis. Relationships between NIR spectra of surface sediment samples and measured lake-water pH values, and between NIR spectra of sediment cores and historical pH values inferred by diatom analysis, are modelled by partial least squares regression. The prediction errors of the models are comparable to those obtained by modelling of diatom and lake-water pH data. By further development NIR spectroscopy can become useful for inferring past pH, as well as several other lake-water parameters, from sediment cores. Diatom-based predictive models, using multivariate calibration methods, are developed for inferences of lake-water pH, alkalinity and colour. These models are used to provide a regional assessment of recent lake acidification in the provinces of Västerbotten and Norrbotten, northern Sweden. The study shows that a pH decline has occurred in some southeastern lakes, but that most of the lakes have not faced significant changes in lake-water pH, alkalinity and colour. The inferred water chemistiy changes are discussed in relation to atmospheric deposition and land-use. In a study of eight acid-sensitive Swedish boreal-forest lakes a past-analogue approach is used to test whether contemporary expansion of conifers could cause lake acidification. Water chemistry changes associated with the natural pre-historic colonization and expansion of spruce in Sweden (≈3000 years B.P.), at times of background atmospheric acidity, are inferred to evaluate the acidification ability of spruce per se on surface waters. This study shows that under natural, unpolluted conditions spruce colonization and expansion did not cause lake acidification. In a synthesis of palaeolimnological acidification research in Sweden a general model for pH- development for acid clear-water lakes in southern Sweden is presented. The pH-development from the last deglaciation to present time can be divided into four different periods; (i) a natural long-term acidification period (12000 B.P. - 2300 B.P., or later), with a gradual decrease in pH resulting from declining fluxes of base cations from catchment soils; (ii) a human induced alkalization period (2300 B.P. - 1900 A.D.), with a pH increase due to human activities in the catchments; (iii) the recent acidification period (about 1900 A.D. - present), when pH decreased towards 4.5 due to acid deposition and possibly ceased land-use; and (iv) the liming period (1970s - present), when pH often increases to values above 7 following lime treatment to counteract acidification. The implications of these past pH changes for the concept of contemporary lake acidification and for liming policy are outlined.
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The long-term effects of large-scale changes in forestry, agriculture and other land use on habitats and the large-scale expansion of wind farming  affects bats foraging environments. In order to predict consequences of exploitations on local bat species and populations, good surveys are important. To get good background information for an Environmental Impact Assessment (EIA) it  is crucial to rapidly assess which areas are most important for bats. The aim of this work was to measure the importance of the two types of forest environment for bats foraging : forest areas located close to or far from the lakes. Bat activity and species diversity was measured with automatic ultrasound recorders in 211  nights of fieldwork at 155 locations in 23 areas in different parts of Sweden during June, July and the first two weeks of August 2011 and 2012. A total of 11 species were recorded in forest far from lakes and 8 species in forest close to lakes. Eptesicus nilssonii , Myotis sp. and Pipistrellus pygmaeus were the most common taxa in both habitat types. Activity levels were higher in the vicinity of lakes compared to forests far away from lakes. Species diversity calculated on base on Chao 2 was similar for both types of habitats . The results suggest that the forests close to lakes are the most important habitats to surveys for bats in Sweden and that inventory efforts should be primarily invested in them.

Alpine lakes are among the most remote aquatic environments in Europe. Although remote, their small size and the high turnover of surface waters render alpine catchments extremely receptive and vulnerable to anthropogenic impact on a local (i.e., water abstraction, tourism, introduction of alien species) and a global scale (long-range transport of pollutants, acid rain, global warming). Alpine lakes are indicators of global environmental change and “early warning systems” for the mountain environment. Many studies have considered single lakes or groups of lakes; however, because of the wide extent of the Italian Alpine area together with the difficulty of sampling, there have been few studies of the Alpine lakes as a whole. Since it was not possible to extend the research to all Italian Alpine lakes, two lakes (Balma Lake, Cottian Alps, 2100 m a.s.l. and Dimon Lake, Carnic Alps, 1872 m a.s.l.) were selected for this study according to the following criteria: a) the geographic location of the research groups involved in the project, Department of Life Sciences, University of Trieste and Istituto Zooprofilattico Sperimentale del Piemonte, Liguria e Valle d’Aosta; b) site geomorphology and accessibility; 3) presence of fish after introduction for recreational fishing. The main aims of this PhD project were: a) conduct ecological characterization based on biotic components (macrobenthic invertebrates, benthic diatoms, ostracods and fish); b) study the pressures and changes via analysis of biotic components; c) obtain background data for future research. The overarching objectives were: 1) obtain topographic and bathymetric maps of lakes using new technologies (drones); 2) characterize the hydrochemistry; 3) characterize macrobenthic invertebrates, benthic diatoms and ostracods since typical biological components of Alpine lakes and widely used to assess ecological status of surface freshwater; 4) investigate changes in chironomids, ostracods and benthic diatoms composition over time based on paleolimnological analysis. These biological components can yield information to different perturbations and, given a good time-control, it is possible to estimate phases and amplitudes of disturbance; 5) investigate environmental contamination through trace elements detection in macrobenthic invertebrates; 6) characterize fish communities, obtaining information about their biological and sanitary condition. Sampling was performed during the ice-free season (summer and autumn of 2017 and 2018) at both lakes. The physicochemical features of the lakes were in line with published literature but differed from each other due to the geo-lithological context of the two areas. The biodiversity of the littoral macrobenthic communities was comparable with other high-altitude environments, where Diptera Chironomidae and Oligochaeta generally predominate. Paleolimnological analysis of Balma Lake highlighted significant differences in subfossil chironomid communities before and after the introduction of fish and between modern and subfossil communities, with a significant reduction in diversity. Macrobenthic invertebrates from the two lakes were found to differ in trace element concentration, which was higher in Dimon Lake. Individuals of bullhead (Cottus gobio) and minnow (Phoxinus phoxinus) were captured from Dimon Lake, whereas only brook trout (Salvelinus fontinalis) were captured from Balma Lake, with individuals belonging to age classes 0+ to 4+. Health monitoring revealed hepatic steatosis in C. gobio from Dimon Lake, probably linked to an adaptation of the fish to the winter season. Finally, the analysis of benthic diatoms and ostracods is preliminary, and the results need to be further elaborated and developed in the future. This PhD thesis has produced new data about the ecology and conservation status of two Alpine lakes, which may guide local administrations in their decisions to implement conservation and monitoring plans.

Phytoplankton are single celled organisms capable of phytosynthesis, and are present in all the major oceans and lakes in the world. Phytoplankton contribute to 50% of the total primary production on Earth, and are the dominating primary producer in most aquatic ecosystems. This thesis is based on the 1D deterministic model by Jäger et. al. (2010) which models phytoplankton dynamics in freshwater lakes, where phytoplankton growth is limited by the availability of light and phosphorus. The original model is here extended to two dimensions to include a horizontal dimension as well as a vertical dimension, in order to simulate phytoplankton dynamics under varying lake bottom topographies. The model was solved numerically using a grid transform and a finite volume method in MATLAB. Using the same parameter settings as the 1D case studied by Jäger et. al. (2010), an initial study of plankton dynamics was done by varying the horizontal and vertical diffusion coefficients independently.

[Truncated abstract] Coastal lagoons play an important role in the transport of materials between the coastal zone and the ocean. Understanding the dynamics associated with the movement of waters between and within these systems is therefore significant in defining the ecological health of the system. An important sub category of lagoons is Intermittently Closing and Opening Lakes and Lagoons (ICOLLs). These systems lack any significant river inflow; have a restricted sill type inlet and experience intermittent exchange with the ocean, making them susceptible to the retention of nutrients and pollutants from the catchment. The duration and frequency of an opening event may vary from weeks to months between each ICOLL, and inter and intra annually, respectively, and during an opening event, there are appreciable fluctuations in water level (1-3m range) accompanied by large changes in salinity (7 30ppt) within a short timeframe (hours). . . Regardless of the processes complete oceanic flushing was still predicted for each system, by the end of their respective opening events. The modelling work successfully reproduced the spring tidal setup in water level and exchange, using real bathymetry and meteorological forcing and defined the spring tidal set-up as the key predictable process in the exchange of water and salt between the larger ICOLL and the ocean. It was also shown that strong winds had the capacity to influence the magnitude of the exchange. The overall outcomes of this research therefore include the identification of key physical processes associated with the variability of the hydrodynamics within and between ICOLLs, which will aid in the future management of these highly dynamic systems.

Lake Superior is a forcing factor for local weather systems, causing substantial amounts of lake effect snow in the winter (particularly on the south shore). This study assesses decreasing ice cover of Lake Superior and its effects upon synoptic weather factors. Data were collected from eleven National Weather Service (NWS) stations located on the south shore of the lake. Rainfall and snowfall amounts from December to May were regressed on percent ice coverage and average monthly temperatures from 1972-2002. Ice coverage and average monthly temperature had a negative relationship with snowfall and rainfall.

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.

Mogan and Eymir Lakes, located 20 km south of Ankara, are important aesthetic, recreational, and ecological resources. DikilitaS and ikizce reservoirs, constructed on upstream surface waters, are two man-made structures in the basin encompassing an area of 985 km2. The purpose of this study is (1) to quantify groundwater components in lakes&rsquo
budgets, (2) to assess the potential impacts of upstream reservoirs on lake levels, and (3) to determine effects of potential climatic change on lakes and groundwater levels in the basin. Available data have been used to develop a conceptual model of the system. The three dimensional groundwater model (MODFLOW) has been developed for the system. The model has been calibrated successfully under transient conditions over a period of six years using monthly periods. The results show that groundwater inflows and outflows have the lowest contribution to the overall lakes&rsquo
budget. A sensitivity analysis was conducted to determine the limits within which the regional parameters may vary. Three groundwater management scenarios had been developed. The results show that the upstream reservoirs have a significant effect on lake stages but not on groundwater levels. A trade-off curve between the amount of water released and the average stage in Lake Mogan has been developed. The continuation of the existing average conditions shows that there would be declines in groundwater elevations in areas upstream from Lake Mogan and downstream from Lake Eymir. The results also indicated that very small, but long-term changes to precipitation and temperature have the potential to cause significant declines in groundwater and lake levels.

Since the 'discovery' of the high abundance of viruses in aquatic environments, it has been generally assumed that viruses in lakes are similar to those in oceans. I directly compared these two systems using a large, robust data set. Viral abundance was significantly different among the surveyed environments. The relationship between viral and bacterial abundance indicated a fundamental difference between lakes and oceans, and suggested that viruses infecting phytoplankton may be more important in lakes. Molecular techniques (PCR & DGGE) were used to document spatial and temporal variations in the richness of viruses that infect eukaryotic phytoplankton (Phycodnaviridae) in lakes at the Experimental Lakes Area (ELA). Phycodnavirus richness was highest in the eutrophic lake, and during the spring/early summer in all the lakes. Viral richness was closely associated with phytoplankton abundance and composition. As a result, richness was influenced by trophic status, while patterns of richness were affected by regional climatic conditions. Phylogenetic analysis of environmental Phycodnavirus DNA polymerase (pol) sequences indicated that freshwater Phycodnaviruses are genetically different from cultured isolates and marine environmental sequences. A genetic distance analysis indicated that polsequences > 7 % different infected different host species. Therefore, the 20 different freshwater sequences likely infected nine different hosts. Multivariate statistics identified seven possible phytoplankton hosts, including chlorophytes, chrysophytes, diatoms and dinoflagellates. Finally, the modified dilution experiment was evaluated as an approach for estimating viral-mediated phytoplankton mortality in two lakes at the ELA. Experiments resulted in non-significant apparent growth rate regressions. While a model analysis, indicated that the method was sensitive to poorly constrained parameters such as burst size and length of the lytic cycle, making it unsuitable for estimating mortality rates in these lakes. These studies indicate that Phycodnaviridae are a genetically rich and dynamic component of lakes. Their richness is influenced by both the chemical and physical components of their environment. Although the presence of these viruses indicates that they are a source of phytoplankton mortality, the magnitude of their impact on structuring phytoplankton communities awaits methodological advances. Nonetheless, these findings support the view that viruses infecting phytoplankton are ecologically important componentsof lake ecosystems.