• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 193
  • 53
  • 11
  • 9
  • 4
  • 4
  • 3
  • 1
  • Tagged with
  • 279
  • 279
  • 46
  • 46
  • 46
  • 42
  • 38
  • 35
  • 31
  • 30
  • 22
  • 20
  • 19
  • 19
  • 19
  • About
  • 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.
61

Energy intake of Common Guillemot, <em>Uria aalge</em>, chicks at Stora Karlsö, Sweden : influence of changes in the Baltic Sea

Enekvist, Elisabeth January 2003 (has links)
<p>Observations of feeding behaviour of common guillemots, <em>Uria aalge</em>, in June 2002 at the island Stora Karlsö in the Baltic Sea proper, and measurements of morphology and energy density in the prey fish sprat, <em>Sprattus sprattus</em>, showed that fish delivered to chicks at present are shorter and weigh less than in the 1970s. Long lasting attending periods and a feeding rate of 4.6 feeds per day indicate that parents are feeding their chicks at a maximum rate. Because of a decline in the energy density in sprat (22.4 kJg<sup>-1</sup> dry weight) the daily energy intake of common guillemot chicks have declined noticeably. This could probably explain the observed decrease in fledging body weight of chicks through the 1990s. Baltic common guillemots do not seem to be able to select more energy-dense prey sizes or to switch to other prey species.</p>
62

Küsten und Klimawandel in den Augen von Touristen : eine Wahrnehmungsanalyse an der deutschen Ostsee / How do tourists percieve the coast and climate change? : A perception analysis at the Baltic Sea

Hallermeier, Larissa Diane January 2011 (has links)
Aufgrund seiner wirtschaftlichen Bedeutung spielt der Tourismus in Mecklenburg-Vorpommern eine große Rolle. Insbesondere die Küstengebiete sind beliebte Reiseziele. In den letzten Jahren konnte ein kontinuierlicher Anstieg der Ankünfte und Übernachtungen verzeichnet werden. Neben anderen Faktoren werden die regionalen Auswirkungen des Klimawandels jedoch in Zukunft eine Herausforderung für den Tourismussektor darstellen. Die globale Erwärmung wird für den Strand- und Badetourismus sowohl negative, als auch positive Folgen haben, auf die reagiert werden muss. Neben vorbeugenden Klimaschutzmaßnahmen werden künftig auch Anpassungsstrategien entwickelt werden müssen, die den zu erwartenden Veränderungen Rechnung tragen. Doch zu welchen tourismusrelevanten Veränderungen wird es überhaupt kommen und was geschieht bereits aktuell? Sind die Folgen des Klimawandels durch Touristen schon jetzt wahrnehmbar? Wie reagieren die Urlauber auf eventuelle Veränderungen? Diese und andere Fragen soll die vorliegende Arbeit, die innerhalb des RAdOST-Vorhabens (Regionale Anpassungsstrategien für die deutsche Ostseeküste) angesiedelt ist, beantworten. Dazu wurde zum einen eine Literaturrecherche zu tourismusrelevanten Klimawandelfolgen an der deutschen Ostseeküste durchgeführt. Zum anderen erfolgte in den Sommermonaten 2010 eine Befragung der Strandgäste in Markgrafenheide, Warnemünde und Nienhagen an der mecklenburgischen Ostseeküste. Im Mittelpunkt der Umfrage stand die Wahrnehmung von Erscheinungen (z.B. viele Quallen oder warmes Ostseewasser) sowie kurz- oder langfristigen Veränderungen an der Küste (z.B. schmalere Strände, vermehrter Strandanwurf) durch die Urlauber. Außerdem wurden die Einstellung und der Informationsgrad der Gäste zum Thema Klimawandel an der Ostseeküste analysiert. Ziel war es, aus den Umfrageergebnissen Handlungsempfehlungen für das lokale Strandmanagement hinsichtlich künftiger Anpassungsstrategien abzuleiten. Die Literaturrecherche zeigte, dass in einigen Bereichen schon jetzt Veränderungen (z.B. der Luft- und Wassertemperatur oder des Meeresspiegels) nachweisbar sind und laut verschiedener Modellprojektionen von weiteren Veränderungen ausgegangen werden kann. Wie die Umfrage deutlich machte, sind die Veränderungen momentan durch Touristen jedoch kaum oder gar nicht wahrnehmbar. Dementsprechend gering ist auch ihre Reaktion auf die einzelnen Phänomene. Generell ist die Wahrnehmung der Urlauber sehr subjektiv und selektiv. Manche Gegebenheiten wie beispielsweise existierende Küstenschutzmaßnahmen werden von einem großen Teil der Touristen gar nicht wahrgenommen. Hinsichtlich anderer Erscheinungen wie Strandanwurf und Quallen sind viele Besucher wiederum sehr sensibel. Es zeigte sich außerdem, dass es für die meisten Urlauber schwierig ist, zu beurteilen, ob bestimmte Gegebenheiten am Strand und an der Küste mit der globalen Erwärmung in Verbindung stehen oder nicht. Es besteht eine große Unsicherheit zu diesem Thema und oft wird der Klimawandel als Ursache für Erscheinungen genannt, auch wenn der kausale Zusammenhang wissenschaftlich nicht nachzuweisen ist. Es zeigte sich, dass die Urlauber sehr wenig über die regionalen Auswirkungen des Klimawandels informiert sind, sich aber Informationen wünschen. Folglich sollte zunächst die Aufklärung und Information der Urlauber über die Folgen der Veränderung des Klimas im Vordergrund stehen. Denn manche Aspekte, wie der Verlust von Strandabschnitten durch Erosion oder eine eventuelle Zunahme von Blaualgen in der Sommersaison, können nicht gänzlich vermieden werden. Durch gezielte Aufklärung könnte jedoch beispielsweise eine Akzeptanz für naturnahe Strände oder für den Rückzug aus einzelnen Gebieten geschaffen werden. Darüber hinaus sollte die zu erwartende Saisonverlängerung systematisch genutzt werden, um sowohl die Küste, als auch das Hinterland durch gezielte Angebote für Touristen attraktiv zu machen. Auf diese Weise könnte eine Entzerrung der Hauptsaison und eine bessere Auslastung der Beherbergungsbetriebe sowie der touristischen Infrastruktur erreicht werden.
63

Deposit-feeding in benthic macrofauna : Tracer studies from the Baltic Sea

Byrén, Lars January 2004 (has links)
A low content of organic matter, which is largely refractory in nature, is characteristic of most sediments, meaning that aquatic deposit-feeders live on a very poor food source. The food is derived mainly from sedimenting phytodetritus, and in temperate waters like the Baltic Sea, from seasonal phytoplankton blooms. Deposit-feeders are either bulk-feeders, or selective feeders, which preferentially ingest the more organic-rich particles in the sediment, including phytodetritus, microbes and meiofauna. The soft-bottom benthos of the Baltic Sea has low species biodiversity and is dominated by a few macrobenthic species, among which the most numerous are the two deposit-feeding amphipods Monoporeia affinis and Pontoporeia femorata, and the bivalve Macoma balthica. This thesis is based on laboratory experiments on the feeding of these three species, and on the priapulid Halicryptus spinulosus. Feeding by benthic animals is often difficult to observe, but can be effectively studied by the use of tracers. Here we used the radioactive isotope 14C to label food items and to trace the organic matter uptake in the animals, while the stable isotopes 13C and 15N were used to follow feeding on aged organic matter in the sediment. The abundance of M. balthica and the amphipods tends to be negatively correlated, i.e., fewer bivalves are found at sites with dense populations of amphipods, with the known explanation that newly settled M. balthica spat are killed by the amphipods. Whether the postlarvae are just accidentally killed, or also ingested after being killed was tested by labelling the postlarvae with 14C and Rhodamine B. Both tracer techniques gave similar evidence for predation on and ingestion of postlarval bivalves. We calculated that this predation was likely to supply less than one percent of the daily carbon requirement for M. affinis, but might nevertheless be an important factor limiting recruitment of M. balthica. The two amphipods M. affinis and P. femorata are partly vertically segregated in the sediment, but whether they also feed at different depths was unknown. By adding fresh 14C-labelled algae either on the sediment surface or mixed into the sediment, we were able to distinguish surface from subsurface feeding. We found M. affinis and P. femorata to be surface and subsurface deposit-feeders, respectively. Whether the amphipods also feed on old organic matter, was studied by adding fresh 14C-labelled algae on the sediment surface, and using aged, one-year-old 13C- and 15N-labelled sediment as deep sediment. Ingestion of old organic matter, traced by the stable isotopes, differed between the two species, with a higher uptake for P. femorata, suggesting that P. femorata utilises the older, deeper-buried organic matter to a greater extent. Feeding studies with juveniles of both M. affinis and P. femorata had not been done previously. In an experiment with the same procedure and treatments as for the adults, juveniles of both amphipod species were found to have similar feeding strategies. They fed on both fresh and old sediment, with no partitioning of food resources, making them likely to be competitors for the same food resource. Oxygen deficiency has become more wide-spread in the Baltic Sea proper in the last half-century, and upwards of 70 000km2 are now devoid of macrofauna, even though part of that area does not have oxygen concentrations low enough to directly kill the macrofauna. We made week-long experiments on the rate of feeding on 14C-labelled diatoms spread on the sediment surface in different oxygen concentrations for both the amphipod species, M. balthica and H. spinulosus. The amphipods were the most sensitive to oxygen deficiency and showed reduced feeding and lower survival at low oxygen concentrations. M. balthica showed reduced feeding at the lowest oxygen concentration, but no mortality increase. The survival of H. spinulosus was unaffected, but it did not feed, showing that it is not a surface deposit-feeder. We conclude that low oxygen concentrations that are not directly lethal, but reduce food intake, may lead to starvation and death in the longer term.
64

Phytobenthic communities in the Baltic Sea - seasonal patterns in settlement and succession

Qvarfordt, Susanne January 2006 (has links)
Seasonal changes in reproduction, recruitment, occurrence and growth of marine plant and animal species is a common phenomenon world-wide. This thesis investigates whether such seasonal changes could determine the succession in subtidal phytobenthic communities on free space in the Baltic Sea. My results showed circular seasonal patterns both in the settlement of species and in the annual appearance of communities. The circular seasonal pattern was also observed in the succession. Initial species assemblages were determined by the time space became available for colonisation. Although the succession seemed to be directed towards one site-specific final community structure determined by physical factors, the time of the year when space became available influenced the rate of the succession through species interactions. Rapid growth and timing of settlement and free space occurrence allowed early species to occupy all available space and prevent further colonisation, thereby slowing the succession. My results also showed that both settlement and community structure are influenced by substrate characteristics. Studying community development on vertical artificial structures revealed communities with few species and different composition compared to communities on vertical natural substrates. A field study showed that settlement and community structure changed significantly between 60º and 90º substrate slopes. This thesis shows that some differences in the final community structure are determined already at the settlement stage and that the succession pattern varies depending on when free space occurs. However, small inter-annual and site-specific differences in seasonal settlement periods and site-specific final communities mainly determined by physical factors, suggest that succession patterns are relatively predictable. Seasonal changes seem to cause a spiralling succession towards a final, seasonally undulating, state.
65

Filamentous cyanobacteria in the Baltic Sea - spatiotemporal patterns and nitrogen fixation

Almesjö, Lisa January 2007 (has links)
Summer blooms of filamentous, diazotrophic cyanobacteria are typical of the Baltic Sea Proper, and are dominated by Aphanizomenon sp. and the toxic Nodularia spumigena. Although occurring every summer, the blooms vary greatly in timing and spatial distribution, making monitoring difficult and imprecise. This thesis studies how the spatial variability of Baltic cyanobacterial blooms influences estimates of abundance, vertical and horizontal distribution and N2-fixation. Implications for sampling and monitoring of cyanobacterial blooms are also discussed. The results of the thesis confirm the importance of diazotrophic cyanobacteria in providing N for summer production in the Baltic Proper. It also highlights the large spatial and temporal variation in these blooms and argues that improved spatial coverage and replication could make monitoring data more useful for demonstrating time trends, and for identifying the factors regulating the blooms. The vertical distribution of Aphanizomenon and Nodularia was found to be spatially variable, probably as a combination of species-specific adaptations and ambient weather conditions. Vertical migration in Aphanizomenon was more important towards the end of summer, and is probably regulated by a trade-off between P-availability and light and temperature.
66

On methods for estimating oceanic flow

Nilsson, Jenny A. U. January 2008 (has links)
The aim of this thesis was to estimate and possibly quantify ocean flow by utilizing conventional and novel observational methods as well as model results. Motionally induced voltages, from a cable-based observational system in the Baltic Sea, were analysed to determine their utility for ocean monitoring. The data set was examined as regards the influence of single- and multi-layer flow. Correlation analyses undertaken in the first study showed that the geoelectric installation is capable of providing good estimates of the net flow across the Visby-Västervik transect. The second study focused on possible effects of multi-layer flow on the signal. Comparisons were made with tidal-gauge geostrophic flow estimates, and a good agreement was found, except for a few brief winter periods characterized by significant discrepancies. The velocity fields from a three-dimensional model showed that these events coincided with strong surface and bottom currents, and hence the attenuated voltage signal was suggested as being caused by the non-uniform velocity distribution. The third study dealt with the deep-water flow through the Understen-Märket trench. Observational data indicated that this flow could be described by applying hydraulic theory. Since the passage is narrow compared to the internal Rossby radius of deformation, rotational effects could be neglected to lowest order. The theoretical predictions proved to agree well with the observational results. The final study examined the effects of the heat flux and the wind forcing on the circulation in Bahía de Concepción, Chile, where three field surveys were undertaken during the extended austral summer 2002. Hydrographic and current measurements were compared to local tidal-gauge records. Rough estimates of the barotropic and the baroclinic flow across the transect indicated an unusual vortex circulation during periods of weak wind forcing and strong surface heating; results which were corroborated by numerical simulations.
67

Operatörernas attityder till säkerhet på finlandsfärjorna / The operators' attitudes towards safety on the ferries Sweden-Finland

Magnusson, Helena January 2010 (has links)
Passagerarna behöver mera tid än säkerhetsinformation eftersom passagerarna har så bråttom att komma ombord, boka bord och handla tax-free. Därmed missar passagerarna viktig säkerhetsinformation som alltid ges vid avgång via fartygets högtalarsystem. Det finns klar och tydlig säkerhetsinformation ombord. Det viktiga är sättet att ge information än att ge mera information. Idag informeras passagerarna via videoskärmar, utrymningskartor på hyttdörrar, via högtalarsystemet ombord, säkerhetsbroschyrer i hytter och information, välutbildad besättning och det är väl skyltat ombord. Att överinformera om riskerna ombord kan skapa en oro bland passagerarna. Passagerarna är oftast ute på nöjeskryssningar och vill inte bli påminda om tidigare fartygskatastrofer eller om risker. Det är upp till varje passagerare att söka säkerhetsinformation och hur passagerarna tar till sig säkerhetsinformationen beror till viss del på deras attityd och intresse att ta till sig säkerhetsinformationen. Det finns säkerhetsinformation att tillgå ombord och detta ger passageraren ett väsentligt bättre utgångsläge att klara sig om det bli aktuellt att utrymma fartyget. Det är svårt att få information om säkerheten innan avgång, eftersom passageraren hänvisas till rederiernas hemsida. Rederierna skyltar inte med säkerhetsinformation på startsidan, utan passageraren måste själv leta sig vidare till denna information. Rederierna har en god säkerhetskultur och med detta menas, safety first och ständig förbättring.
68

Preventive action in the protection of the Baltic Sea : Do the HELCOM Baltic Sea Action Plan and An Agenda for the Baltic Sea Region – Baltic 21 advocate preventive action in protecting the Baltic Sea?

Lundgren, Lina January 2008 (has links)
The Baltic Sea is a sensitive and unique ecosystem that has been strongly affected by human activity in the area. It is an important cultural and natural resource that contributes with several economic benefits. Among the many documents aiming to protect the Baltic Sea, this thesis concerns two of the action plans; An Agenda for the Baltic Sea Region – Baltic 21 and HELCOM Baltic Sea Action Plan, which are two of the most recognised documents aiming at protecting the Baltic Sea area. The two documents was analysed using three different types of text analysis. As the main goal in all environmental protection is to urge preventive action in protecting the environment, the two documents will be analysed with the aim of investigating whether preventive action is advocated in the protection of the Baltic Sea, even though the region is threatened and have many problems from an environmental point of view. The two documents differ structurally as their approaches differ. The HELCOM Baltic Sea Action Plan (BSAP) has an ecosystem approach, whiles the Baltic 21 has sustainable development as its primarily approach. The results of the study further show that preventive action is advocated in both documents. However, the BSAP presents a cleared preventive approach and suggests more preventive action than Baltic 21. Baltic 21 lack a clear connection to the Baltic Sea and instead focus in the whole Baltic Sea area. There are few clearly preventive action presented in the protection of the actual Baltic Sea in Baltic 21. Instead the Baltic 21 shows a vague argumentation and few actions aiming at preventing environmental harm to the Baltic Sea.
69

Bis(4-chlorophenyl) sulfone and PCB methyl sulfone metabolites : Trends and chirality in the Baltic Sea environment

Norström, Karin January 2006 (has links)
The Baltic Sea was earlier identified as a highly polluted brackish water body and still is. The high concentrations of polychlorinated biphenyls (PCBs), p,p’-DDT and related compounds led to severe effects on several species in the Baltic region. However, the situation has improved significantly since the 1970’s resulting in lower exposures to a range of pollutants and healthier wildlife populations. Independent of this positive trend there are still new chemicals leaking into the Baltic Sea environment. The objective of this thesis is to improve the knowledge of sulfone containing compounds and pollutant metabolites in wildlife, with special interest in bis(4-chlorophenyl) sulfone (BCPS) distribution, temporal trend and exposure levels, and the methylsulfonyl-PCBs (MeSO2-PCBs). The latter are of particular interest for chiral MeSO2-PCBs. BCPS is used for the production of high temperature polymers and was detected as an environmental contaminant ten years ago. PCBs, p,p’-DDT and related compounds are still of scientific interest. BCPS is biomagnified and especially in the bird guillemot which has levels of up to 2000 ng BCPS/g fat compared to the grey seal with concentrations of about 60 ng/g fat. The seal levels are similar to the herring, the prey of the bird and seal, with concentrations of 30 ng BCPS/g fat. The guillemot concentration of BCPS has been similar over the last 30 years with a minimal, but significant, annual decline of 1.6%. The reason for the slow decline is not yet understood. Also MeSO2-PCBs and 3-MeSO2-DDE show a small decrease over time in guillemot egg (3 and 9%, respectively), which is less then for the parent compounds. This shows that the sulfone metabolites are more persistent than their precursors in the guillemot. Furthermore, all these sulfone containing compounds showed a specific retention to liver comparing different tissues in grey seal. The atropisomers of the chiral MeSO2-PCB were analysed in both the guillemot and the grey seal and showed to occur in a skewed relationship. This is particularly pronounced in seals where one atropisomer of each chiral congener is very dominating. The dominating atropisomers have been identified with an absolute R configuration, in both grey seal and guillemot. An enantioselective metabolism was indicated to occur when experimentally tested by CB-132 in rat. This thesis is stressing the high specificity in wildlife for one atropisomer in the pair of chiral PCB methyl sulfones being PCB metabolites, and the high BCPS concentrations in guillemot hatching in the Baltic proper.
70

Genetic response to pollution in sticklebacks; natural selection in the wild

Lind, Emma January 2013 (has links)
The last century, humans have been altering almost all natural environments at an accelerating rate, including the Baltic Sea that has highly eutrophicated areas and many coastal industries such as Pulp-mills. For animals living in a habitat that changes there are basically two alternatives, either to cope with the change or become locally extinct. This thesis aims to investigate if recent anthropogenic disturbance in the Baltic Sea can affect natural populations on a genetic level through natural selection. First, we found a fine-scale genetic structure in three-spine sticklebacks (Gasterosteus aculeatus) populations along the Swedish coast (paper I), indicating limited gene-flow between populations in geographic proximity. Different genetic markers, specifically Amplified Fragment Lenght Polymorpism (AFLP, and microsatellites,  gave different results, highlighting the heterogeneous character of genomes which demonstrates that it is important to choose a genetic marker that is relevant for the question at hand. With a population genomic approach, and a multilocus genetic marker (AFLP), we detected convergent evolution in genotype composition in stickleback populations living in environments affected by pulp-mill effluent (paper II) and in highly eutrophicated environments (paper III), compared to adjacent reference populations. We found loci, in both studies (paper II, III), that were different from a neutral distribution and thus probably under divergent selection for the habitat differences investigated. The selective effect from pulp-mill effluents were more pronounced, but the two different habitats had mutual characters (AFLP loci). In paper IV, we converted five anonymous AFLP loci to sequenced markers and aligned them to the stickleback genome. Four out of five loci aligned within, or close to, coding regions on chromosome I, chromosome VIII, chromosome XIX and chromosome XX. One of the loci, located on chromosome VIII and identified as under divergent selection in both paper II and III, has been identified in other studies as to be under selection for fresh water adaptation, including Baltic Sea stickleback populations. In conclusion, anthropogenic alterations of natural environments can have evolutionary consequences, probably adaptive, for the animals living there and the evolutionary response exhibited by natural populations can be very fast. / <p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 1: Manuscript. Paper 3: Manuscript. Paper 4: Manuscript.</p>

Page generated in 0.0797 seconds