Fixed nitrogen is important as a nutrient for organic matter formation and as an electron donor (nitrification) and acceptor (denitrification) for energy generation, but it is scarcely available in aquatic systems. Nitrification oxidizes ammonium to nitrite and nitrate. Denitrification uses these fixed species to form dinitrogen gas. The classic understanding of the nitrogen cycle requires dissolved oxygen for nitrification and assumes denitrification reduces nitrate to dinitrogen through various intermediates in anaerobic conditions. The global nitrogen budget is imbalanced with more marine denitrification measrued than previously estimated in the classic nitrogen cycle, suggesting alternative anaerobic nitrification and denitrification pathways exist. One alternative denitrification pathway is anammox, which directly oxidizes ammonium to dinitrogen with nitrite as the electron acceptor. Other alternative pathways for both nitrification and denitrification involve redox metals as catalysts. Manganese-catalyzed anaerobic nitrification and denitrification are thermodynamically favorable at neutral pH. However, experimental evidence for these processes is still lacking. This investigation seeks to uncover evidence of manganese-catalyzed nitrification and denitrification in saltmarsh sediments. Batch reactors with anaerobic sediment slurries from a saltmarsh in coastal Georgia were incubated in the presence and absence of colloidal manganese oxides and isotope-labeled ammonium and nitrate to trace dinitrogen formation. Results show that denitrification is more prominent in the manganese-treated reactors and that the classic denitrification pathway may not be substantial in shallow saltmarsh sediments. These data indicate that anammox and/or manganese-coupled denitrification are major contributors to the removal of fixed nitrogen. Ammonium removal in the manganese-treated reactors is accompanied by a high nitrite production compared to the nitrogen-only treatment, indicating manganese-coupled denitrification exists and/or anammox is promoted in the presence of manganese. Primary productivity is generally high in saltmarshes, but oxygen penetrates less than a few millimeters in the sediment. These observations suggest that oxygenic nitrification does not fuel denitrification below the sediment-water interface. The data show that manganese may play a role in the formation of nitrite and nitrate in oxygen-limited sediments.

Unclear predictions surrounding climate change, associated sea-level rise and potential impacts upon coastal environments have placed an emphasis on the importance of sea-level change. Past sea-level fluctuations have been measured using biological and geomorphological forms of evidence. One such biological proxy is salt-marsh foraminifera, which have been used as a high-resolution indicator of past sea-level change, based on the assumption that surface foraminiferal assemblages are similar in composition to buried fossil foraminifera. In South Africa, there is ongoing research seeking to produce high-resolution records of sealevel change, however foraminifera remain an underutilized source of proxy evidence. This research applies salt-marsh foraminifera as precise indicators of relative sea-level change at Kariega Estuary on the Eastern Cape coastline of South Africa. Distributions of modern foraminiferal assemblages were investigated, revealing vertical zonation across the intertidal zone. The foraminiferal and marsh vegetation zones were in part similar and overlapped to a certain extent, identifying three zones; high, low and tidal flats. This suggested foraminiferal distribution is a direct function of elevation relative to tidal fluctuation. A 94 cm core consisting of peat, sand and clay sediments was extracted from the salt marsh. A chronological framework for the core was based on five AMS radiocarbon age determinations of both bulk sediment and shell fragment samples placing the record within the last 1500 years Before Present (BP). The basal shell age was a clear outlier to all bulk sediment ages, possibly as a result of shell recrystallisation. The bulk sediment age determinations suggested two possible age reversals, potentially linked to sedimentary hiatus or contamination. These inconsistencies in the chronology were best viewed as separate age models. The core was analysed at a high resolution, whereby fossil foraminifera were extracted every 2 cm’s down the core. A transfer function was applied to calculate the former elevation at which each core sample once existed, to produce a relative sea-level reconstruction. The reconstruction was related to the age models to produce two possible sea-level curve scenarios. Reconstructed curves from both scenarios depict a 0.5 m (±0.16 m) sealevel highstand at 1500 cal years BP followed by a lowstand of -0.6 m (±0.03 m). Scenario One reached its lowest recorded sea-level between 600 cal years BP and 500 cal years BP and then fluctuated below present day levels. Scenario Two reached its lowest recorded sea-level around 1200 cal years BP, followed by low amplitude fluctuations and a relatively stable period from 100 cal years BP till the present day. The 1500 cal years BP highstand recorded for both scenarios correlates well with existing palaeoenvironmental literature from the southern African coastline. Chronological limitations associated with the remainder of the record hinder inter-comparison with previous studies. The outcomes of this research suggest that intertidal saltmarsh foraminifera demonstrate enormous potential for the high-resolution reconstruction of relative sealevel change in the South African context. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2013.

Thesis (M.S.)--University of Hawaii at Manoa, 2006. / Includes bibliographical references (leaves 98-106). / vii, 106 leaves, bound 29 cm

Thesis (M.S.)--University of North Carolina Wilmington, 2008. / Title from PDF title page (viewed September 22, 2008) Includes bibliographical references (p. 60-62)

Thesis (Ph. D.)--Florida State University, 2005. / Advisor: Dr. Joel Kostka, Florida State University, College of Arts and Sciences, Dept. of Oceanography. Title and description from dissertation home page (viewed June 22, 2005). Document formatted into pages; contains xi, 108 pages. Includes bibliographical references.

Thesis (Ph. D.)--University of California, Berkeley, 2006. / Includes bibliographical references.

Thesis (Ph.D.)--University of North Carolina at Wilmington, 2006. / Includes bibliographical references (leaves: 198-208)

Thesis (M.S.)--University of Delaware, 2005. / Principal faculty advisor: Ronald E. Martin, Dept. of Geology. Includes bibliographical references.

No description available.

Tidal exchanges of organic carbon, nitrogen and phosphorus between a south temperate Sarcocornia marsh and its associated estuary are examined. Subterranean water flow was small, and the hydraulic exchange between the two systems largely surficial. The dominant tidal signal was semi-diurnal, and the extent of inundation of the marsh varied considerably as a consequence of interactions of semi-lunar tidal cycles with changes in daily mean sea level. Annual net fluxes of organic carbon were directed from the marsh to the estuary, but amounted to less than 2% of marsh aerial net primary productivity. This indicates the incompatibility of E.P. Odum's outwelling hypothesis to this marsh-estuarine system. The direction of net flux of organic carbon switched on a time-scale of days. These directions were largely correlated with mesoscale oceanic events, which materially altered the extent of marsh inundation, and which provided evidence of the mutual exclusivity of outwelling of DOC from the marsh and oceanic upwelling. Laboratory mesocosm experiments using intact marsh blocks of sediment from the marsh were conducted to identify the proximate processes and interactions at the marsh-water interface responsible for the variability of marsh-estuarine exchanges. Patterns of fluxes of organic carbon, total nitrogen and phosphorus were markedly different in the structurally contrasted tidal creek and Sarcocornia Zone regions of the marsh. Both regions exported these components, but the fluxes of organic carbon and total phosphorus were significantly larger from the tidal creek than from the Sarcocornia zone, and the opposite applied to nitrogen. The presence of brachyuran crabs . the most numerous macrofauna on the marsh enhanced the flux of carbon, nitrogen and phosphorus from the marsh biocoenosis, largely as a result of the effect of their bioturbation. Evidence is examined which suggests that differential mobilization of nutrients in the two zones by crabs is responsible for biogeochemical coupling of these two regions , which may account for the elevated productivity of salt- marsh systems