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Estuarine phytoplankton growth is often controlled by nitrogen availability. In addition to overall nitrogen loads, nitrogen form (organic vs. inorganic) is an important factor affecting estuarine phytoplankton growth and community composition. Recent studies have shown that in addition to nitrogen availability, trophic cascades and relaxation of grazing pressure may also be important for phytoplankton bloom formation in estuaries. With a goal of better understanding how nitrogen availability and grazing pressure interact to control estuarine phytoplankton growth and community composition, we examined the individualistic as well as the combined effects of nitrogen (varying availability and form) and grazing pressure on estuarine phytoplankton growth and community composition in the Neuse River Estuary, North Carolina, USA. During each of three sampling events (June 2011, August 2011, March 2012) natural phytoplankton assemblages were manipulated with added nitrogen (as urea or nitrate) and reduced grazing pressure (by filtering out zooplankton grazers). Treatments were incubated for 48 hours in an experimental pond, and subsamples taken daily to assess phytoplankton growth responses to treatments through chlorophyll a, diagnostic photopigments and cell enumerations. The effects of nitrogen additions and reduced grazing pressure varied throughout the events. In June, only nitrogen addition stimulated phytoplankton community growth (chlorophyll a), while in August, only grazing reduction had a significant impact on community growth. Neither treatment had a significant effect on community growth in March, as the phytoplankton community faced phosphorus-limitation and decreased grazing pressure associated with cooler winter/spring temperatures. While both treatments did not continuously effect overall phytoplankton growth throughout all experiments, there were always effects seen in some diagnostic photopigments, indicating varying taxa-specific responses to treatments throughout the year, which can be explained by shifts in phytoplankton community composition and environmental factors. These results demonstrate the importance of both bottom-up (nutrient availability and form) and top-down (grazing) controls in a temperate, eutrophic estuary. Results also hint at the potential for other factors (i.e. light and phosphorus-limitation) to play a role in phytoplankton growth as well. Phytoplankton growth, biomass and community dynamics are relevant indicators of environmental change and this study highlights the need to consider the potential interactive effects of controlling factors for proper management of estuarine ecosystems.

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This thesis describes the design, optimisation and shipboard deployment of a flow injection - chemiluminescence (FI-CL) technique for the determination of iron (Fe) in seawater. Chapter One presents an overview of the marine biogeochemistry of Fe, including its speciation, sources and sinks, abundance and limitation for phytoplankton growth in the Wodd*s oceans. Current analytical methods for the determination of Fe in natural waters are also reviewed. Chapter Two reports the instrumental development of the FI - CL method. Each component is described and its suitability to the flow manifold discussed. Different CL detection systems are evaluated and a charge coupled device used to investigate the spectral profile of the Fe-catalysed luminol reaction. Automation of the FI manifold is also detailed along with acquisition of CL signals. Chapter Three details the optimisation of a FI - CL procedure for the determination of Fe in seawater. Reagent clean-up techniques, blank procedures and a standard addition operating routine are detailed. Fe(III) reduction using sulphite is treated theoretically. Matrix effects are investigated and the synthesis of an 8-hydroxyquinoline resin used for in-line matrix elimination and preconcentration is reported. The optimised method is selective to Fe(II+IIl) in the linear range 0.04-10 nM, with a precision of 3.2% (n=5) for a LO nM standard and a limit of detection (3s) of 40 pM for a load time of 1 min. Chapter Four presents the results of an investigation into the kinetic effect of Fe on luminol CL using the continuous addition of reagent (CAR) technique. Instrumental and chemical parameters are optimised, interferences investigated and the CAR-CL technique compared with alternative flow configurations. In Chapter Five, the application of the F - CL method to the shipboard determination of Fe in the surface North and South Atlantic (SO'^N to 50°S) is presented. Data are reported for samples collected from the upper water column (<200 m) in eight different biogeochemical provinces, which represent coastal, upwelling and oligotrophic regions of the Adbntic Ocean. Total dissolvable iron (unfiltered, TD-Fe) levels range ftom <0.1 to 6.1 nM and indicate that high and spatially variable TD-Fe (>2 nM) concentrations exist in Equatorial and tropical North Atlantic regions influenced by atmospheric deposition from the West African continent. Away from strong input mechanisms, TD-Fe concentrations in the upper water column average 0.6 nM. Input sources are fingerprinted via correlation with other trace metals (Al, Co, Ni), nutrients and hydrography, whilst active biological uptake is shown to be the dominant sink. TD-Fe vertical distributions through the upper mixed layer display strong relationships with chlorophyll a concentrations, and measurements in the deep chlorophyll maximum of the South Atlantic oligotrophic gyre show that, despite elevated nitrate at such depths, Fe concentrations are at a minimum (ca. 0.1 nM) and may be low enough to (co-)limit phytoplankton growth.

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Diss. (sammanfattning) Uppsala : Uppsala universitet, 2005. / Felaktig titel på omslag och rygg: Climate effect on phytoplankton biomass and functional groups. Härtill 5 uppsatser.

Thesis (M.S.)--University of Toledo, 2008. / Typescript. "Submitted as partial fulfillments of the requirements for The Master of Science Degree in Biology (Ecology-track)." "A thesis entitled"--at head of title. Bibliography: leaves 19-23.

Thesis--University of Wisconsin. / Vita. Includes bibliographical references (leaves 164-169). Photocopy of typescript. Ann Arbor, Mich. : University Microfilms, 1972.-21 cm. Also issued in print.

Thesis (M.S.)--Rutgers University, 2010. / "Graduate Program in Oceanography." Includes bibliographical references.