Thesis (Ph. D.)--Joint Program in Chemical Oceanography (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 2013. / Cataloged from PDF version of thesis. / Includes bibliographical references. / Iron is a redox active trace metal micronutrient essential for primary production and nitrogen acquisition in the open ocean. Dissolved iron (dFe) has extremely low concentrations in marine waters that can drive phytoplankton to Fe limitation, effectively linking the Fe and carbon cycles. Understanding the marine biogeochemical cycling and composition of dFe was the focus of this thesis, with an emphasis on the role of the size partitioning of dFe (<0.2 jm) into soluble (sFe<0.02 jm) and colloidal (0.02ptm<cFe<0.2 m) size fractions. This was accomplished through the measurement of the dFe distribution and size partitioning along basin-scale transects experiencing a range of biogeochemical influences. dFe provenance was investigated in the tropical North Atlantic and South Pacific Oceans. In the North Atlantic, elevated dFe (>I nmol/kg) concentrations coincident with the oxygen minimum zone were determined to be caused by remineralization of a high Fe:C organic material (vertical flux), instead of a laterally advected low oxygen-high dFe plume from the African margin. In the South Pacific Ocean, dFe maxima near 2000m were determined by comparison with dissolved manganese and 3He to be caused by hydrothermal venting. The location of these stations hundreds to thousands of kilometers from the nearest vents confirms the "leaky vent" hypothesis that enough dFe escapes precipitation at the vent site to contribute significantly to abyssal dFe inventories. The size partitioning of dFe was also investigated in order to trace the role of dFe composition on its cycling. First, the two most commonly utilized methods of sFe filtration were compared: cross flow filtration (CFF) and Anopore filtration. Both were found to be robust sFe collection methods, and sFe filtrate through CFF (10 kDa) was found to be only 74±21% of the sFe through Anopore (0.02pjm) filters at 28 locations, a function of both pore size differences and the natural variability in distribution of 1 OkDa- 0.02 [m colloids. In the North Atlantic, a colloidal-dominated partitioning was observed in the surface ocean underlying the North African dust plume, in and downstream of the TAG hydrothermal system, and along the western Atlantic margin. However, cFe was depleted or absent at the deep chlorophyll maximum. A summary model of dFe size partitioning in the North Atlantic open ocean is presented in conclusion, hypothesizing that a constant dFe exchange between soluble and colloidal pools modulates the constant partitioning of nearly 50% dFe into the colloidal phase throughout the subsurface North Atlantic Ocean, while sFe and cFe cycle independently in the upper ocean. / by Jessica Nicole Fitzsimmons. / Ph.D.

Thesis (S.M.)--Joint Program in Chemical Oceanography (Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 2013. / Cataloged from PDF version of thesis. / Includes bibliographical references. / Nitrogen and trace metal biogeochemical effects on phytoplankton productivity were compared through whole water bottle incubations and proteomic evaluation of in situ harvested particulate matter from two distinct oceanographic regions: the Equatorial Pacific Upwelling and the South Pacific Gyre. Phytoplankton growth in both regions was stimulated by nitrogen additions with equivalent response from nitrate and urea. In the gyre, trace metal additions did not yield a chlorophyll response, however nickel treatments showed evidence of nickel-limited nitrogen fixation. In contrast, cell growth at the upwelling site was primarily iron-limited and iron plus urea or nitrate additions further enhanced the chlorophyll response, indicative of secondary nitrogen limitation. Nitrogen stress proteins and urea transporters from cyanobacteria in these field sites showed similar trends, with both increasing in waters containing lower dissolved inorganic nitrogen. Together with bottle incubations, the abundant urea transporters and nitrogen stress proteins indicate the importance of urea in these field sites. Representative cyanobacteria cultures (Synechococcus strain WH8020, and Prochlorococcus strain MED4) were evaluated to constrain urea uptake rates and explore the potential for compound specific uptake rates. Together, results from this study indicate that urea may represent an under-recognized component of the marine microbial nitrogen cycle. / by Tyler Jay Goepfert. / S.M.

The Kafue Flats floodplain wetland system in southern Zambia is under increasing climate and human pressures. Firstly, drought episodes appear more prevalent in recent years in the region and secondly, two dams were built on the lower and upper ends of the wetland in 1972 and 1978, respectively, across the Kafue River which flows through the wetland. The study uses multi-temporal remote sensing to assess change in extent and vigour of green vegetation, and extent of water bodies and dry land cover on the Kafue Flats. The change detection's management value is assessed. Four normalised, co-registered digital Landsat images from 24 September 1984, 3 September 1988, 12 September 1991 and 20 September 1994 were used. The main change detection method used was comparison of classifications, supplemented by Normalised Difference Vegetation Index (NDVI) and Principal Component Analysis (PCA) change detection. Ancillary land use and environmental data were used in interpreting the change in the context of cause and effect. The results indicate inconsistent trends in the changes of most land cover classes, as a result of manipulation of the wetland by man through annual variations in the timing and magnitude of regulated flows into the wetland, as well as burning. However, the results also show spatial reduction in the wetland's dry season dense green reed-grass vegetation in upstream sections which are not affected by the water backing-up above of the lower dam. Sparse green vegetation is replacing the dense green vegetation in these upstream areas. It is inferred that this dry season degradation of the wetland threatens bird species which may use the reeds for dry season nesting. It is proposed that ground surveying and monitoring work at the micro-habitat level is necessary to ascertain the implications of the losses. It is concluded that, in spite of difficulties, multi-temporal remote sensing has a potential role in wetland change assessment on the Kafue Flats at the community level, but that it needs to be supplemented by targeted, micro-habitat level ground surveys.

Evidence is presented to support the conclusions that (1) North Lake reservoir is less productive, contains lower standing crops of phytoplankton and total organic carbon than other local reservoirs; (2) that neither the phytoplankton nor their instantaneously-determined primary productivity was detrimentally affected by the power plant entrainment and (3) that the effect of the power plant is to cause nutrient limitation of the phytoplankton primary productivity by long-term, subtle, thermally-linked nutrient precipitation activities.

Thesis (M.S.)--University of North Carolina at Wilmington, 2005. / Includes bibliographical references (leaves: 40-41)

Thesis (doctoral)--Uppsala University, 1985. / Includes bibliographical references (p. [92]-98).

Accurate estimation of Net Primary Productivity (NPP), which is a key component of the terrestrial carbon cycle, is very important in studies of global climate. Ecosystem models have been used for NPP estimates. Determining how much each source of uncertainty contributes to modeled NPP is veiy important before ecosystem models can be used with confidence over larger areas and time periods. This research has systematically evaluated the boreal ecosystem productivity simulator (BEPS) carbon model in mountainous terrain, Kananaskis, Alberta. After parameterization of the model, sensitivity analysis was conducted as a controlled series of experiments involving sensitivity simulations with BEPS by changing a model input value in separate model runs. The results showed that NPP was sensitive to most model inputs measured in the study area, but that the most important input variables for BEPS were LAI and forest species. In addition, the NPP uncertainty resulting from topographic influence was approximately 3.5 %, which is equivalent to 140 kg C ha"1 yr"1. This suggested that topographic correction for the model inputs was also important for accurate NPP estimation. Using the topographically corrected data, the carbon dynamics were simulated, and average annual NPP production by forests in Kananaskis was estimated at 4.01 T ha"1 in 2003. / xix, 117 leaves : col. ill. ; 29 cm.

Responses of periphyton and phytoplankton productivity in the lower Sulphur River (Texas-Arkansas) to bleach-kraft mill effluent (BKME) were monitored using in situ ¹⁴C incubation. Carbon assimilation rates measured downstream of mill discharge were substantially reduced from upstream levels. Periphyton and phytoplankton chlorophyll a concentrations remained relatively unchanged by the presence of BKME. Periphyton ash-free dry weight increased near the mill outfall, but decreased further downstream. Calculated productivity efficiencies (productivity:biomass) varied with variations in ¹⁴C rates. A laboratory bioassay was designed to determine the effect of BKME light-attenuation on photosynthetic rates of upstream Sulphur River periphyton and Selenastrum capricornutum Prinz. Pooled results of bioassay runs indicated a 20 per cent BKME concentration effectively reduced control ¹⁴C-assimilation levels by 50 per cent. The downstream reduction observed for in situ productivity was 5 per cent lower than that predicted by the color bioassay.

The link between aboveground net primary productivity (ANPP) and resource gradients generated by complex terrain (solar radiation, nutrients, and moisture) has been established in the literature. Belowground ecosystem stocks and functions, such as soil organic carbon (SOC), dissolved organic carbon (DOC), and belowground productivity have also been related to the same topography and resource distributions, and therefore it is expected that they share spatial and temporal patterns with ANPP. However, stand structure on complex terrain is a function of multiple trajectories of forest development that interact with existing resource gradients, creating feedbacks that complicate the relationships between resource availability and ANPP. On a 96 ha forested watershed in the H.J. Andrews Experimental Forest in the Western Cascades range of Oregon, spatiotemporal heterogeneity in the secondary succession of a replanted Pseudotsuga menziesii stand following harvest results from the interaction of stand composition and abiotic drivers and may create unique "hot spots" and "hot moments" that complicate gradient relationships. In this dissertation, I tested the hypotheses that (chapter 3) multiple successional trajectories exist and can be predicted from a general linear model using specific topographic, historical, and biological parameters and that an estimated "maximum ANPP" may better represent stand characteristics than ANPP measured at a particular moment in time. I also test that (chapter 4) the distribution of light fraction carbon (LFC; C with a density of less than 1.85 g/cm��) is spatially variable, elevated on hardwood-initiated sites (hardwood biomass > 50% of biomass), and positively correlated with litter fall and ANPP. Chapter 4 also tests that heavy fraction carbon (HFC; C with a density of greater than 1.85 g/cm��) is a function of both soil mineralogy, stand composition, and ANPP, such that edges observed spatially in site mineralogy (changes in soil type) are reflected in sharp changes in the composition of the forest community and the magnitude of HFC stores. Finally, I hypothesized (chapter 5) that in complex terrain, dissolved organic carbon (DOC) export can be predicted from landform characteristics, relates to ANPP, and may be measured by several methods which are well-correlated with one another. In chapter 6, I discuss how litter fall measurements can be extrapolated to a watershed extent, and use litter fall as an example of the error that can occur in scaling up measurements taken at a small scale, within a heterogeneous stand on complex terrain, to a landscape scale extent. / Graduation date: 2013