Studies were undertaken to examine the roles of iron and carbon in modulating prokaryotic growth in the ocean. The context of the first study was an open-open iron fertilization experiment in the high nutrient, low chlorophyll (HNLC) regime in the Southern Ocean. The context of the second study was the oligotrophic, iron-replete, and organic carbon-limited northwest Sargasso Sea. Experimental sea water cultures were amended with an iron chelator, desferrioxamine B (DFOB), and other nutrients to examine the effects of iron and carbon limitation on growth. In the first study prokaryotic abundance, carbon production, and growth rate increased in response to iron in two experimental locations north and south of the Antarctic Polar Front Zone (North Patch and South Patch, respectively). However, prokaryotes responded indirectly to iron-induced phytoplankton production. Prokaryotic production was highly correlated to particulate primary production (r2 = 0.80). Prokaryotes comprised a larger percentage of particulate organic carbon (POC) in the North versus the South Patch relative to non-fertilized waters. Analysis of prokaryotic community structure was also examined. Results showed unique prokaryotic communities existed in the North and South Patch for both iron-fertilized and non-fertilized waters. Additionally, community composition shifted over time in the South Patch and was distinct from non-fertilized waters. Measures of community diversity indicated an increase in taxonomic richness and diversity in iron-fertilized waters over time. Specific taxonomic groups monitored over time in the South Patch exhibited a differential response to the iron-induced phytoplankton bloom. at the domain level, the biomass response was greater for Eubacteria compared to Archaea. at the clade level, Cytophaga-Flavobacteria net biomass yields outpaced SAR11, although both exhibited significant increases (p < 0.05) in net growth rate over time in the South Patch. In the second study DFOB did not limit utilization of organic carbon (glucose). Conversely, DFOB stimulated prokaryotic growth in a dose-dependent manner. The trend of the response to DFOB was similar to glucose; however, the magnitude of the response (i.e. growth rate and biomass yield) at higher equivalent carbon doses was greater than that of glucose. Additionally, DFOB and glucose elicited a differential taxonomic response.

Continental shelves are generally believed to play a critical role in ocean biogeochemical cycling, however this has raised the question as to the relative importance of various nitrogen flux terms such as denitrification, burial, net community production and advective fluxes. Quantifying these fluxes on an annual area-integrated basis using traditional observational means is often difficult, due to the fact that these fluxes rapidly change on relatively small spatial scales, making inadequate data resolution a significant problem. Satellite remote sensing data and numerical modeling provide alternative ways to fill the data gaps, and hence have the potential to generate quantitative estimates of these various biogeochemical fluxes. However, they both suffer from distinct shortcomings, e.g., satellite data are only limited to the surface whereas numerical modeling can be pointless without rigorous skill assessment. Thus caution is warranted when using these tools to generate quantitative estimates of biogeochemical fluxes. The two were combined in this dissertation project by assimilating the satellite-derived data into the models, selecting the optimal ecosystem model, as well as evaluating the model before using the model simulations to explore the nitrogen fluxes on the Mid-Atlantic Bight (MAE). First, multiple satellite-derived data products were assimilated into a one-dimensional assimilative model framework to determine the relative advantages of assimilating different satellite data types. The variational adjoint method, a parameter optimization method, was applied to a series of experiments assimilating synthetic and actual satellite-derived data, including total chlorophyll, size-fractionated chlorophyll and particulate organic carbon (POC). The experiments revealed the importance of assimilating data from multiple sites simultaneously as the optimal parameter sets produced by assimilating data at individual sites were often unrealistically over-tuned and deteriorated model skill at times and depths when data were not available for assimilation. The model-data misfits from the experiments also demonstrated that optimal results were obtained when satellite-derived size-differentiated chlorophyll and POC were both assimilated simultaneously. These two types of satellite data were then assimilated simultaneously to rigorously evaluate how food web model complexity affects the ability of a lower trophic level model to reproduce observed patterns in satellite-derived data. This was again implemented in the one-dimensional model framework to minimize the computational costs. Five ecosystem model variants with various levels of complexity in the phytoplankton (P) and zooplankton (Z) structures were examined by assimilating satellite-derived size-differentiated chlorophyll and POC data at four MAE continental shelf sites, and testing the optimal parameter values at five independent sites in a cross-validation experiment. Although all five models showed improvements in model skill after the assimilation, the moderately complex 2P2Z model best reproduced the surface fields throughout the MAE. Additional experiments were conducted in which random noise was added to the satellite data prior to assimilation. Whereas the most complex model was sensitive to the random noise added to the data, the simpler models successfully reproduced nearly identical optimal parameters regardless of whether or not noise was added to the assimilated data, highlighting that random noise inherent in data into these simple models. The moderately complex 2P2Z ecosystem model was thus coupled with a three-dimensional circulation model and forced by a dynamic land ecosystem/watershed model to simulate the biogeochemical cycling on the MAB shelf and to quantitatively assess key components of the annual area-integrated nitrogen budget from 2004-2007. The simulation indicated that over these four years similar amounts of nitrogen were removed by denitrification and burial (∼0.1 Tg N y-1). Net community production was larger and varied more between the four years (∼0.2 to 0.3 Tg N y-1), but overall was positive, indicating that the MAB was net autotrophic. The advective fluxes of nitrogen into and out of the MAB were dramatically different between the four years investigated (by about ∼.26 Tg N y-1), presumably as a result of changes in the positions of the Gulf Stream and Labrador Sea waters. The accumulative effects of these fluxes resulted in a near zero net rate of change in total nitrogen, indicating the MAB remained unchanged in the amount of total nitrogen in the water column over these the four years. Sensitivity tests varying the initial conditions and simplifying the modeled plankton structure showed distinct impacts on these nitrogen fluxes: the former strongly affected the advective fluxes, but had little impact on denitrification, burial or NCP, whereas the latter significantly reduced denitrification, burial, and NCP but did not significantly impact the advective fluxes. Overall the strong seasonality and interannual variability in the nitrogen fluxes highlight the importance of data coverage throughout all seasons and multiple years in order to accurately resolve the current status and future changes of the MAB nitrogen budget.

Dissolved and suspended particulate organic carbon (DOC, POC), nitrogen (DON, PON), phosphorus (DOP, POP) and inorganic nutrient distributions and elemental ratios were measured and evaluated for the Atlantic, Southern, and Pacific Oceans. Results indicate that DOC is remineralized during mean deep-water transport from the North Atlantic to the North Pacific. Elemental ratios for both dissolved organic matter (DOM) and particulate organic matter (POM) indicate that organic N is preferentially remineralized compared with organic C, while organic P is preferentialy remineralized relative to both organic C and N. Comparison between the DOM and POM pools further suggests that surface POM may be less refractory than concurrently sampled DOM. Major compound class compositions of ultrafiltered DOM (UDOM) in the North Atlantic, North Pacific and Chesapeake Bay indicate that the majority of UDOM was comprised mainly of a molecularly-uncharacterized fraction, followed by carbohydrates, proteins and lipids. Delta14C and delta 13C results of UDOM compound classes suggest that UDOM in Bay mouth and surface open ocean waters were similarly dominated by old, marine sources, while UDOM from the freshwater endmember was influenced by much younger terrestrial sources. Results indicate that DOM is comprised of different aged organic fractions and provide evidence for a potential organic "size"-age continuum; from low-molecular weight DOM (oldest) to UDOM (intermediate age) to POM (youngest). Lipid biomarker results indicate that North Atlantic and Pacific UDOM and POM were relatively more reactive at the surface compared with greater depths, coinciding with elemental C:P and N:P ratios greater than Redfield. Factor analyses suggest that there exists a "lability continuum" spanning from surface ocean POM to riverine and deep ocean UDOM. Terrigenous organic material was found at all Bay sites although autochthonous sources of organic matter were also important. Dark microbial incubations of DOM from the Pacific Subtropical Front and South Atlantic Bight indicate that open ocean DOM is relatively refractory over short time scales (less than 2 months). Experiments with plankton leachate DOM show that this sub-pool of DOM is relatively labile and is converted to refractory DOM within days. DOP is preferentially remineralized in all experiments compared with DOC or DON.

Includes bibliographical references.

Thesis (Ph. D.)--College of William and Mary. / Vita. Includes bibliographical references.

Three laboratory studies were performed to elucidate the influence of soil texture, pH, and cation exchange capacity (CEC) on the concentration of ferrous Fe in soil solution and the resulting expression of soil redoximorphic features. The objectives were: 1) assess the buffering effects of CEC on ferrous Fe concentration in soil solution, 2) evaluate the effects of pH on the concentration of ferrous Fe in soil solution, and 3) observe the expression of redoximorphic features in soils with varying texture and CEC. The studies concentrated on seasonally wet soils from the Texas Gulf Coast Prairie. Selected soils included Alfisols and Vertisols with characteristics ranging from coarse-loamy to very-fine in texture, strongly acidic to neutral in soil reaction, and siliceous, mixed, and smectitic in mineralogy. The soils included the Pledger clay microlow (acidic, fine-textured), Pledger clay microhigh (neutral, fine-textured), China clay (acidic, fine-textured), Cieno loam (acidic, fine-loamy), Orelia sandy clay loam (neutral, fine-loamy), Gessner fine sandy loam (acidic, coarse-loamy), and Orelia fine sandy loam (neutral, coarse-loamy). The studies provided the following information: 1) fine-textured soils with higher CEC contained more ferrous Fe in solution, 2) ferrous Fe concentrations in the acidic fine-loamy and coarse-loamy soils were higher than the neutral soils for the same textural class, 3) acidic and neutral fine-textured soils contained more ferrous Fe in solution than the remaining soils, 4) the highest percentage of redox concentrations was observed in the acidic, fine-textured soil, 5) the acidic fine-loamy and coarse-loamy soils exhibited a greater percentage of Fe depletions, and 6) a higher percentage of redox features were observed by micromorphic analysis (i.e., point counts under a binocular stereoscopic microscope) than by macromorphic descriptions. This research showed that differing soil characteristics affect the reductive dissolution and translocation of Fe, and subsequent formation of redox features.

Thesis (M.S.)--Miami University, Dept. of Geology, 2003. / Title from first page of PDF document. Document formatted into pages; contains vii, 127 p. : ill. Includes bibliographical references (p. 108-113).

Thesis (M.S.)--Lehigh University, 2009. / Advisers: Robert K. Booth; Joan M. Ramage. Includes supplementary digital materials.

Thesis (M.S.) in Civil Engineering--University of Maine, 2002. / Includes vita. Includes bibliographical references (leaves 76-85).

Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2009. / Source: Dissertation Abstracts International, Volume: 70-06, Section: B, page: 3378. Adviser: Atul Jain. Includes bibliographical references (leaves 137-150) Available on microfilm from Pro Quest Information and Learning.