Influence of protozoan grazing on the marine geochemistry of particle reactive trace metals
type: CreativeWork
description: Planktonic protozoan grazers have the potential to significantly affect the chemistry of particle-associated trace metals. This is due both to the importance of protists as consumers of bacterial-sized particles, and to the unique low-pH, enzyme-rich microenvironment of the grazer food vacuole. This thesis examines the role of protozoan grazers in the marine geochemistry of strongly hydrolyzed, particle-reactive trace metals, in particular Th and Fe. A series of tracer experiments was carried out in model systems in order to determine the effect of grazer-mediated transformations on the chemical speciation and partitioning of radioisotopes C9Fe, 234Th, 51Cr) associated with prey cells. Results indicate that protozoan grazers are equally able to mobilize intracellular and extracellular trace metals. In some cases, protozoan regeneration of trace metals appears to lead to the formation of metal-organic complexes. Protozoan grazing may generate colloidal material that can scavenge trace metals and, via aggregation, lead to an increase in the metal/organic carbon ratio of aggregated particles. Model system experiments were also conducted in order to determine the effect of grazers on mineral phases, specifically colloidal iron oxide (ferrihydrite). Several independent techniques were employed, including size fractionation ors9Fe-labeled colloids, competitive ligand exchange, and iron-limited diatoms as "probes" for bioavailable Fe. Experimental evidence strongly suggests that protozoan grazing can affect the surface chemistry and increase the dissolution rate of iron oxide phases through phagotrophic ingestion. In further work on protozoan-mediated dissolution of colloidal Fe oxides, a novel tracer technique was developed based on the synthesis of colloidal ferrihydrite impregnated with 133Ba as an inert tracer. This technique was shown to be a sensitive, quantitative indicator for the extent of ferrihydrite dissolution/alteration by a variety of mechanisms, including p…
abstract: Planktonic protozoan grazers have the potential to significantly affect the chemistry of particle-associated trace metals. This is due both to the importance of protists as consumers of bacterial-sized particles, and to the unique low-pH, enzyme-rich microenvironment of the grazer food vacuole. This thesis examines the role of protozoan grazers in the marine geochemistry of strongly hydrolyzed, particle-reactive trace metals, in particular Th and Fe. A series of tracer experiments was carried out in model systems in order to determine the effect of grazer-mediated transformations on the chemical speciation and partitioning of radioisotopes C9Fe, 234Th, 51Cr) associated with prey cells. Results indicate that protozoan grazers are equally able to mobilize intracellular and extracellular trace metals. In some cases, protozoan regeneration of trace metals appears to lead to the formation of metal-organic complexes. Protozoan grazing may generate colloidal material that can scavenge trace metals and, via aggregation, lead to an increase in the metal/organic carbon ratio of aggregated particles. Model system experiments were also conducted in order to determine the effect of grazers on mineral phases, specifically colloidal iron oxide (ferrihydrite). Several independent techniques were employed, including size fractionation ors9Fe-labeled colloids, competitive ligand exchange, and iron-limited diatoms as "probes" for bioavailable Fe. Experimental evidence strongly suggests that protozoan grazing can affect the surface chemistry and increase the dissolution rate of iron oxide phases through phagotrophic ingestion. In further work on protozoan-mediated dissolution of colloidal Fe oxides, a novel tracer technique was developed based on the synthesis of colloidal ferrihydrite impregnated with 133Ba as an inert tracer. This technique was shown to be a sensitive, quantitative indicator for the extent of ferrihydrite dissolution/alteration by a variety of mechanisms, including p…
author: Barbeau, Katherine A.
language: en_US
keywords: Protozoa, Water chemistry, Trace elements in water, Marine zooplankton, Chemistry
date published: 1998-05
date modified: 2026-07-27T22:05:06Z
provider: Woods Hole Oceanographic Institute
publisher: Networked Digital Library of Theses and Dissertations
type: WebPage
source organization: Massachusetts Institute of Technology and Woods Hole Oceanographic Institution

PropertyValue
property ID: Handle
value: https://hdl.handle.net/1912/5153

PropertyValue
property ID: DOI
value: 10.1575/1912/5153