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  • 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.

A systems approach to pelagic ecosystem dynamics in an estuarine environment

Iverson, Richard L. 22 December 1971 (has links)
Phytoplankton dynamics in Auke Bay, Alaska, were studied during summer, 1969. Nitrate, chlorophyll a, particulate organic carbon, phytoplankton and zooplankton species composition and hydrographic and meteorological data were collected and analyzed. Nitrate input into Auke Bay through freshwater runoff was negligible. A bloom of Thalassiosira aestivalis formed the spring bloom in Auke Bay in 1969. No phytoplankton bloom occurred during a June period when winds were light and variable. Two major blooms of Skeletonema costatum occurred after periods when Auke Bay surface layers were mixed by wind-induced turbulence. The water column became nearly isothermal after periods of high wind mixing although a pronounced density and halal structure persisted, a consequence of input of freshwater to the bay from Auke Creek. Examination of fecal pellets collected from the bay and results of laboratory grazing experiments suggested that Skeletonema costatum was not grazed by zooplankton living in Auke Bay. Nonlinear ordinary differential equations were written to describe phytoplankton and nitrate dynamics in Auke Bay. The phytoplankton dynamics equation included formulations for time-varying insolation and for time-varying wind mixing coefficients. Formulations for effects of nitrate concentration on the photosynthetic assimilation number and for effects of phytoplankton standing crop on the extinction coefficient of light in the water column were included. The nitrate dynamics equation included a formulation for effects of wind-mixing of nitrate-rich water into the euphotic zone from deeper layers of the water column, as well as a formulation for utilization of nitrate in phytoplankton growth. Computer simulation response of the equations reproduced the bloom pattern observed in the field data with some discrepancies caused by assumptions used in model development. The phytoplankton and nitrate model response was strongly coupled to the pattern of the wind-mixing coefficient, as required by the field data. Variations in model parameters had little effect on phase relations between model response and field data but strongly affected model response magnitude. / Graduation date: 1972

Plants, plant communities, net production and tide levels : the ecological biogeography of the Nehalem salt marshes, Tillamook County, Oregon /

Eilers, Hio Peter, III. January 1974 (has links)
Thesis (Ph. D.)--Oregon State University, 1975. / Typescript (photocopy). Includes bibliographical references. Also available online.

Investigations into the seasonal deep chlorophyll maximum in the western North Atlantic, and its possible significande to regional food chain relationships /

Ortner, Peter B. January 1977 (has links)
Thesis (Ph. D.)--Woods Hole Oceanographic Institution, 1977. / "October 1978." "Technical report." WHOI-78-59. "AD-A060 220." Includes bibliographical references (p. 201-220).

Studies on the development of fouling communities on experimental panels in Langstone Harbour

Schmidt, G. H. January 1983 (has links)
No description available.

The ecology of the Manx strand line

Andrews, James Ward January 1991 (has links)
No description available.

Heavy-metal pollution and its effects on recent foraminiferids from Southampton Water, southern England, UK

Sharifi, Abdol Rahim January 1991 (has links)
No description available.

The impact and management of visitor pressure on Rocky Shore communities

Fletcher, Helen January 1997 (has links)
No description available.

Ecological investigations of the British intertidal nephtyidae (Annelida : polychaeta)

Morgan, P. J. January 1984 (has links)
No description available.

Interactions between settling organisms and molluscs in the rocky intertidal

Holmes, Sebastian Paul January 1998 (has links)
No description available.

Anadromous Pike in the Baltic Sea

Engstedt, Olof January 2011 (has links)
The pike (Esox lucius) is a major predator and top-down regulator in the Baltic Sea where it exists in two sympatric forms. One spawn in streams and rivers and the other one spawn in the sea. During the last decades, the habitats for both of these forms have developed in a negative way. In some freshwater systems, up to 90 % of the water areas have disappeared, mainly through drainage and straightening of watercourses for agricultural purposes. In the sea, reproduction habitats decrease due to construction of harbours and human activities that create disturbances. The perhaps largest single factor negatively affecting recruitment of pike in the sea is the eutrophication. Bottoms are overgrown with filamentous algae and shallow bays are covered with dense Phragmites belts decreasing the habitats suitable for spawning. Further on, a predator on egg and fish larvae, the three-spined stickleback (Gasterosteus aculeatus) has increased in abundance. It is difficult to restore and enhance pike production in the sea and probably the only economically viable alternative is to make restorations in freshwater. However, there is a limited knowledge about the freshwater spawning pike in the Baltic Sea. Thus in this thesis I, together with my coauthors, set out with an aim to increase the knowledge base regarding anadromous pike behaviour. We found that pike of natal freshwater origin were common in the Baltic Sea. Through Sr:Ca studies in otoliths, about 45 % of the pike were interpreted to be of freshwater origin. The majority of the pike had emigrated out of freshwater at a length below 6 cm. These results indicate that freshwater recruitment is successful, contrasting the vast areas available for spawning in the sea. This creates incitements that restoration measures in these watercourses could have a significant effect on the pike population in the Baltic Sea. Further, in four streams running out in the Baltic Sea, more than three thousand pike were marked to study spawning migration. About 30-40 % returned to the same river the subsequent year. Most of the pike used the lower parts of the stream for spawning. The homing of pike to a watercourse indicate that freshwater pike in the Baltic Sea consist of specific populations and this is crucial information when taking decisions on fish restoration measures. Three wetlands adjacent to streams were restored for pike production. The most successful restoration involved minimal digging, with flooded grasslands providing optimal conditions for spawning. The first spawning season after restoration increased the pike production hundredfold. In conclusion, the anadromous pike are numerous in the Baltic Sea. To compensate for the decline in pike populations in the sea, “pike-factories” created along the coastline are probably the most justifiable option.

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