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The Global ETD Search service is a free service for researchers
to find electronic theses and dissertations. This service is
provided by the
Networked Digital Library of Theses and Dissertations.
Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
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Showing 251 to 260 of 269 (0.018 seconds)Spelling suggestions: "subject:"bloom"" "subject:"loom""
| 251 |
Methods to Monitor Lake Erie's Harmful Algal Blooms: A Fellowship with the Cooperative Institute for Great Lakes ResearchFyffe, Deanna Lynne 30 November 2017 (has links)
No description available.
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| 252 |
Harmful Algal Blooms in Small Lakes: Causes, Health Risks, and Novel Exposure Prevention StrategiesMrdjen, Igor 28 September 2018 (has links)
No description available.
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| 253 |
Protecting Public Health at Inland Ohio Beaches: Development of Recreational Water Quality Indicators Predictive of Microbial and Microcystin ExposureMarion, Jason W. 20 October 2011 (has links)
No description available.
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Skyfallens hot mot Mälarens ekosystem / The effects of high precipitation on phosphorus transport in three tributaries to Lake Mälaren, SwedenImmo, Nelly January 2024 (has links)
Hälsosamma ekosystem försörjer oss med livsviktiga resurser och tjänster – ekosystemtjänster så som skydd mot översvämning. I Norra Östersjöns vattendistrikt, som Mälaren tillhör, är statusen på den ekosystemtjänsten dålig. Detta beror till stor del på en omfattande dikning och brist på svämplan i området. Under perioder med skyfall riskerar därför området runt Mälaren och dess tillrinnande vattendrag att drabbas av översvämningar som skadar matproduktion, infrastruktur och miljö. Övergödning är redan ett problem i området och stora tillskott av fosfor till följd av översvämmade jordbruksmarker kan orsaka stora algblomningar och försämrad livsmiljö för vattenlevande organismer. Under augusti och september 2023 föll ovanligt stora mängder regn över mellersta Sverige vilket ökade vattenföringen i vattendragen runt Mälaren och översvämmade vissa av dem. Högfrekventa turbiditetsmätningar från in-situ sensorer installerade i Sagån, Hågaån och Fyrisån, tre vattendrag i Mälarens avrinningsområde, har använts för att undersöka skyfallens effekter på deras vattenföring och beräknad fosfortransport. Resultaten visade en signifikant korrelation mellan ökad vattenföring och ökad fosfortransport, en signifikant ökning under 2023 jämfört med 2018–2022 och signifikanta skillnader mellan vattendragen. Översvämmade Sagån hade extremt höga toppar i beräknad fosfortransport. Resultaten indikerar att övergödningsproblemen i Mälaren kan förvärras i ett framtida klimat med mer intensiva skyfall om inte åtgärder tas för att stärka avrinningsområdets förmåga att hantera stora mängder nederbörd. / Healthy ecosystems provide us with vital resources and services – ecosystem services such as flood protection. In the North Baltic Sea Water District, to which Lake Mälaren belongs, the status of that ecosystem service is poor, largely as a result of extensive draining in the area leading to a lack of floodplains. During periods of torrential rain, the area around Lake Mälaren and its tributaries is therefore at risk to be affected by floods that cause damage to food production, infrastructure and the environment. Eutrophication is already a problem in the area and large additions of phosphorus as a result of flooded agricultural land can cause large algal blooms and degraded habitat for aquatic organisms. During August and September 2023, unusually large amounts of rain fell over central Sweden, which increased the flow of water in Lake Mälarens tributaries and flooded some of them. High frequency turbidity data from in-situ sensors installed in Sagån, Hågaån and Fyrisån, three tributaries to Lake Mälaren, was used to study the effects of the heavy rains on their waterflow and estimated phosphorus transport. The results showed a significant correlation between increased water flow and increased phosphorus transport, a significant increase in 2023 compared to 2018-2022 and significant differences between the tributaries. Flooded Sagån had extremely high peaks in estimated phosphorus transport. The results indicate that the eutrophication problems in Lake Mälaren may worsen in a future climate with more intense downpours unless measures are taken to strengthen the catchment's ability to handle large amounts of rainfall.
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Itämeren rehevöitymisen uudistettu diagnoosi ja paradigmaLappalainen, K. M. (K. Matti) 01 June 2018 (has links)
Abstract
The eutrophication of the Baltic Sea continues despite decrease of the external phosphorus load by as much as 80% of the target confirmed by HELCOM. The aim of this thesis is to investigate this paradox, critically evaluate previous explanations for the persistent eutrophication, and to introduce a new diagnosis and paradigm for the causes and processes behind eutrophication of the Baltic Sea.
According to the current consensus, anthropogenic nutrient loading is nearly the sole cause of eutrophication and regular cyanobacterial blooms. However, this study shows that the areal phosphorus loading rate, when modeled properly, is surprisingly low, and unlikely to be the primary cause of eutrophication. Instead, the frequency of the salt water pulses has decreased dramatically during the past 40 years. This is the root cause of eutrophication, via the hyper-vicious cycle of the hypoxic and finally anoxic conditions of the deeps causing internal phosphorus loading, denitrification, and nitrogen and carbon fixation. Furthermore, this work confirms that nitrogen fixation increases in low nitrogen conditions, further increasing eutrophication and cyanobacterial blooms. Thus, the most effective way to break the cycle of eutrophication is to improve the oxygen conditions of the deeps, which really is impossible to achieve by decreasing external loading alone.
A key result of this work is that natural processes, rather than human activity, plays a decisive role in the eutrophication process – a perspective that typically faces substantial resistance. This thesis discusses how sociological and political views have affected the scientific community and its pursuit to model the mechanisms of eutrophication of the Baltic Sea.
In conclusion, this study leads to important novel insights by providing new models for calculating the external and internal phosphorus loads of the Baltic Sea, with results highlighting the importance of natural processes of internal loading from the anoxic deeps. Altogether, this thesis introduces a new a paradigm for eutrophication of the Baltic Sea. / Tiivistelmä
Itämeri rehevöityy edelleen, vaikka fosforikuormitusta on vähennetty 80 % tavoitellusta. On siis syytä tutkia miksi Itämeren tila ei ole parantunut.
Syntyneen ristiriidan ratkaisemiseksi tarkoituksena on etsiä aiemmista tulkinnoista ristiriitoja, korjata ne ja uudistaa tietopohja uudeksi ja toimivammaksi paradigmaksi. Virhetulkintojen tunnistamiseen sovelletaan Popperin falsifikaatiomenettelyn periaatteita.
Konsensuksen mukaan ihmisperäinen kuormitus on lähes yksinomainen syy (sinilevä)rehevyyteen. Kuitenkin Vollenweiderin mallin mukaan tehty, hydrologialla painotettu fosforin pintakuormitus on ollut 1970 - 1980-luvuilla vain lievää rehevyyttä edellyttävällä tasolla. Ulkoinen kuormitus ei siten voi olla suurin rehevyyden aiheuttaja.
Sinilevärehevyyttä ylläpitävänä päätekijänä on syvävesiin happea tuovien suolavesipulssien toistuvuuden romahtaminen. Siitä syntyneet syvävesien ja -pohjien hapettomuudet aiheuttavat Gotlanninmeressä sekä sisäistä kuormitusta että lisärehevöittävää typen- ja hiilensidontaa. Yhdessä näitä prosesseja nimitetään nyt supernoidankehäksi.
Johtopäätöksiä:
• Ihmistieteelliset ja ympäristöpoliittiset näkemykset vaikuttavat luonnontieteellisiin tulkintoihin luultua enemmän.
• Suolavesipulssien harventuminen on hapettomuus- ja rehevyyskierteen perussyy.
• Syvänteiden hapettomuus on kaikkialle negatiivisesti säteilevä keskeistekijä.
• Itämeren supernoidankehä on purettava saattamalla syvänteet hapellisiksi.
• Hapellisuutta ei voida saada aikaan ulkoisen kuormituksen vähentämisellä.
• Jäljelle jäävät siten teknologiset keinot, joista toteutuskelvollisimmalta näyttää Itämeren hapellisimman ja kylmimmän veden pumppaus 30 metrin syvyydestä syvänteisiin, mikä tehostaa myös pulssivesien virtausta syvänteiden pohjalle.
Tämä väitöskirja sisältää viisi vallitsevasta paradigmasta poikkeavaa tulosta:
1. Itämerelle on kehitetty rehevyyden uusi diagnoosi ja paradigma,
2. Luonto dominoi Itämeren tilaa, ei ihminen,
3. Typensidonnalla on lisärehevöittävä mekanismi,
4. Itämerelle on kehitetty uusi fosforin sisäkuormituksen laskentamenetelmä,
5. Virtuaalisen fosforikuormituksen laskenta.
Ilman Gotlanninmeren syvänteiden hapellisuutta Itämeri on tuomittu pysymään rehevyyden supernoidankehässä, ’kaksinkertaisessa takalukossa’.
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| 256 |
Ties That BindOrlowski, Jessica Marie 23 March 2010 (has links)
I am fascinated by the inner thoughts, the memories, and the cumulative experience that make us each a complex physiological puzzle. From birth, sociological building blocks are constructed forming emotional walls and unexpected doorways, boundaries and comfortable passageways through the architecture of our personalities. My thesis work, which is comprised of ceramic figures and interactive toys, offers playful memory triggers and evocative spaces in which viewers can deconstruct the building blocks of their social persona.
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| 257 |
Begrens én onbegrens : intertekstualiteit in die oeuvre van H.J. Pieterse / Ihette JacobsJacobs, Ihette January 2010 (has links)
This dissertation attempts to investigate the intertextual modus operandi in the oeuvre of H.J. Pieterse, with specific focus on his volumes, Alruin (1989) and Die burg van hertog Bloubaard (2000). The overarching purpose of the investigation is to prove that the author not only uses intertextuality in the sense that one text (literary text) refers to another text (literary and non–literary), or that one text influences another. Pieterse engages in conversation with other texts and re–writes these texts by repositioning them in another context and by adding additional metaphoric meaning to them. The author allows these texts to exchange conversation, to mutually influence one another, and this has as a result that, in his poems, his poetry and his oeuvre, metaphoric lines come into being, which lend a layered meaning to these texts and enrich the possibilities of their interpretation. Thus, a play on multiple meaning develops, which moves between texts: written texts, literary texts, non–literary texts, the author, the reader and the context(s). The conclusion to which this dissertation comes, is that the above mentioned manifestations of meanings, which exist and come into existence within the physically confines of the text, expand this text to a less confined existence in terms of meaning, more unlimited and unbound than what is necessarily allowed by the physically confined nature of the written text. The question thus arises of how the physically limited text take possession of and draws into the texts what lies beyond its physical confines to produce meaning, and how this tension around the limits of the literary text is functionally used. Consequentially, the question that follows is how this happens in the oeuvre of H.J. Pieterse and how the author uses his poetic technique to go beyond the confines of the written text. / Thesis (M.A. (Afrikaans and Dutch))--North-West University, Potchefstroom Campus, 2011.
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| 258 |
Begrens én onbegrens : intertekstualiteit in die oeuvre van H.J. Pieterse / Ihette JacobsJacobs, Ihette January 2010 (has links)
This dissertation attempts to investigate the intertextual modus operandi in the oeuvre of H.J. Pieterse, with specific focus on his volumes, Alruin (1989) and Die burg van hertog Bloubaard (2000). The overarching purpose of the investigation is to prove that the author not only uses intertextuality in the sense that one text (literary text) refers to another text (literary and non–literary), or that one text influences another. Pieterse engages in conversation with other texts and re–writes these texts by repositioning them in another context and by adding additional metaphoric meaning to them. The author allows these texts to exchange conversation, to mutually influence one another, and this has as a result that, in his poems, his poetry and his oeuvre, metaphoric lines come into being, which lend a layered meaning to these texts and enrich the possibilities of their interpretation. Thus, a play on multiple meaning develops, which moves between texts: written texts, literary texts, non–literary texts, the author, the reader and the context(s). The conclusion to which this dissertation comes, is that the above mentioned manifestations of meanings, which exist and come into existence within the physically confines of the text, expand this text to a less confined existence in terms of meaning, more unlimited and unbound than what is necessarily allowed by the physically confined nature of the written text. The question thus arises of how the physically limited text take possession of and draws into the texts what lies beyond its physical confines to produce meaning, and how this tension around the limits of the literary text is functionally used. Consequentially, the question that follows is how this happens in the oeuvre of H.J. Pieterse and how the author uses his poetic technique to go beyond the confines of the written text. / Thesis (M.A. (Afrikaans and Dutch))--North-West University, Potchefstroom Campus, 2011.
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| 259 |
Phytoplankton dynamics in a seasonal estuaryChan, Terence January 2006 (has links)
[Truncated abstract] The Swan River is a highly seasonal estuary in the south-west of Western Australia. Salinity may vary from fresh to marine at various times throughout the estuary, depending mostly on the intensity of freshwater discharge. There are occasional problematic dinoflagellate blooms which have spurred investigation of the dynamics of the phytoplankton community. The objective of this research was to examine how phytoplankton biomass and species' successions are influenced by the multiple variables in the aquatic ecosystem, and, if possible, to determine the dominant factors ... Comparisons of phytoplankton nutrient limitation simulations with experimental observations from field bioassays require further investigation, but reinforce findings that nutrients may only limit phytoplankton biomass when there is a convergence of favourable hydrological and hydrodynamic conditions. The Swan River estuary has undergone substantial hydrological modifications from pre-European settlement. Land clearing has increased freshwater discharge up to 5- fold, while weirs and reservoirs for water supply have mitigated this increase and reduced the duration of discharge to the estuary. Nutrient loads have increased approximately 20-fold from pre-European levels. The individual and collective impacts of these hydrological changes on the Swan River estuary were examined using the hydrodynamic-ecological numerical model. The simulation results indicate that despite increased hydraulic flushing and reduced residence times, increases in nutrient loads are the dominant perturbation, producing increases in the frequency and biomass of blooms by both estuarine and freshwater phytoplankton. By comparison, changes in salinity associated with altered seasonal freshwater discharge have a limited impact on phytoplankton dynamics. Reductions of nutrient inputs into the Swan River estuary from its catchment will provide a long-term improvement in water quality but manipulations of freshwater discharge have the potential to provide a provisional short-term remediation measure allowing at least partial control of phytoplankton bloom potential and eutrophication.
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Fate and transport of POPs in the aquatic environment : with focus on contaminated sedimentsJosefsson, Sarah January 2011 (has links)
Persistent organic pollutants (POPs) are hydrophobic substances that readily sorb to organic matter in particles and colloids instead of being freely dissolved in the water phase. This sorption affects the bioavailability and environmental transport of the POPs. The major part of this thesis concerns the role of sediments as secondary sources of POPs. As the primary emissions decrease, contaminated sediments where POPs have accumulated can become the main source of contamination. If the contaminated sediment by time becomes covered with cleaner layers, the POPs are buried and no longer in contact with the aquatic environment. Experiments in this thesis showed, however, that new invading species can alter the sediment-water dynamics as a result of their bioturbation, i.e. mixing of sediment particles and pore-water. Marenzelleria spp., invading species in the Baltic Sea that burrow deeper than native species, were found to increase the remobilization of buried contaminants. The sediment-to-water flux was inversely related to the burial depth (2-10 cm) of the POP congeners (polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers) and also inversely related to the hydrophobicity of the congener. The flux was therefore most pronounced for less hydrophobic contaminants, which was linked to the bioirrigating behaviour of these species. Marenzelleria spp. also accumulated the buried POPs and increased concentrations in surface sediment. Contaminants previously considered buried at a ’safe’ depth can thus be remobilized as a result of the invasion of Marenzelleria spp. in the Baltic Sea. One method to decrease the remobilization of contaminants from sediments is ’capping’, i.e. a layer of clean material is placed as a cap on the sediment. By amending the cap with active materials, which sequester the POPs and decrease their availability, thinner layers can be used (’active capping’ or ’thin-layer capping’). Results from an experiment with thin-layer capping using different active materials (activated carbon (AC) and kraft lignin) showed that both the sediment-to-water flux and the bioaccumulation by benthic species of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs), hexachlorobenzene (HCB) and octachlorostyrene (OCS) decreased with increased thickness of the cap layer (0.5-5 cm). Amendments with active materials further increased the cap efficiency. AC was more efficient than kraft lignin, and a 3 cm cap with 3.3% AC reduced the flux and bioaccumulation with ~90%. The reduction of the sediment-to-water flux was inversely related to the hydrophobicity of the POP, and reductions in the flux had similar magnitudes as reductions in the concentration in deep-burrowing polychaetes, demonstrating the importance of bioturbation for sediment-to-water transport. In a one-year study on the levels of PCDD/Fs, PCBs, and HCB in a coastal area of the Baltic Sea, the correlations between the POP levels and the levels of particles and organic carbon in the water were found to differ for POPs of different structure and hydrophobicity. The levels of PCDD/Fs decreased to one third in May, which could be related to the increased sedimentation, i.e. water-to-sediment transport, during spring bloom.
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