Date of Award

Summer 1993

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Ocean & Earth Sciences

Program/Concentration

Oceanography

Committee Director

William M. Dunstan

Committee Director

George T. F. Wong

Committee Member

Anthony J. Provenzano, Jr.

Committee Member

Frank E. Scully, Jr.

Abstract

H202 in seawater has complicated sources and sinks. The relative importance of biological regulation of H202 compared to other processes is not well understood. In addition, environmental factors affecting the biological regulation of H202 are largely unknown. Marine phytoplankton was examined for the kinetics of the production and decomposition of H202 in the dark. Effects of varying environmental factors such as light, temperature, salinity, nutrients, amino acids, trace metals and growth phase, were examined. H202 was determined with the scopoletin-fluorescence decay method.

Five out of 11 species produced H202, while all of the 11 species decomposed H202. The relative significance of these species for producing H202 decreased in the order of Pleurochrysis carterae > Isochrysis galbana > Dunaliella tertiolecta > Tetraselmis levis > Emiliania huxleyi, and for decomposing it in the order of Synechococcus sp. = Skeletonema costatum » Tetraselmis levis > Chaetoceros flexosus > Chaetoceros simplex > Isochrysis galbana > Thalassiosira oceanica > Amphidinium carterae > Pleurochrysis carterae > Emiliania huxleyi > Dunaliella tertiolecta. Coccoid or unialgal cells showed a tendency to produce H202, whereas diatoms in chains were more likely to decompose H202. Both the production and decomposition of H202 by these algae followed pseudo-first order reactions. The pseudo-first order rate constants related linearly to algal biomass. The biologically-mediated production and decomposition of H202 showed reaction rate constants (k) ranging from 0.0017 to 0.0072 (fig chl-a'L'^ ^hr'1 for the production of H202 and from 0.0242 to 0.0002 (μg chl-a •L'1)'hr'1 for the decomposition of H202. The studies on the rate kinetics suggested that marine phytoplankton regulates the H202 budget in surface oceans by mediating primarily decomposition of H202 rather than production of H202.

The biological regulation of H202 was not strongly affected by physical environmental factors such as light, temperature and salinity. Among the tested factors, amino acids were the most influential factor enhancing the production of H202. Inorganic nitrogen-limited conditions stimulated phytoplankton to produce more H202 per unit biomass. The production of H202 may be a result of amino acid utilization by nitrogen-starved phytoplankton. However, decomposition of H202 was not affected by the addition of amino acids. Nutrient effects on the decomposition rate constants were much more profound in coastal species than in oligotrophic species. In general, the biological production of H202 was small compared to photochemical production but could be significant in nitrogen-limited conditions whereas biological decomposition of H202 was more important than other removal processes. The results of pure culture studies generally agreed with the results of the field studies. The oligotrophic Sargasso seawater showed biological production of H202 whereas the mesotrophic coastal water displayed predominantly decomposition of H202. Biological production of H202 could occur mostly in inorganic nitrogen-limited conditions by a limited number of species whereas biological decomposition of H202 could remove H202 from most coastal waters by a large number of species. This study implied that nitrogen dynamics as well as phytoplankton species composition and their abundance are necessary to understand biological roles in H202 budget. The regulation of H202 by phytoplankton may also be related to the speciation of trace metals in ambient waters because of strong oxidizing/reducing properties of H202.

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DOI

10.25777/bc73-j634

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