The effect of protozoan grazers on the cycling of polychlorinated biphenyls (PCBs) in marine systems
Citable URI
https://hdl.handle.net/1912/4104Location
Vineyard Sound, MADOI
10.1575/1912/4104Abstract
Processes affecting organic carbon distribution and composition can control the
speciation of organic contaminants such as polychlorinated biphenyls (PCBs) and
ultimately determine their residence time in a particular environment. In marine systems,
the microbial loop influences organic carbon dynamics by recycling a significant fraction
of dissolved and particulate organic matter. The goal of this thesis was to understand
how these recycling processes affect chlorobiphenyl (CB) cycling in marine systems by
monitoring CB dynamics among organic carbon pools represented by dissolved organic
matter, bacterial prey and phagotrophic protozoan grazers.
Initially, I studied the extent to which a protozoan grazer (Uronema sp. - 10μm ciliate)
equilibrated with aqueous PCBs within 2-3 hours. Initial calculations predicted rapid
equilibration via passive diffusion. Experimentally, no difference in equilibration time
was noted between grazing and non-grazing protozoa, indicating that diffusion was the
primary uptake pathway for these organisms. The results were extended to determine the
transition size of an organism where the rates of diffusive and ingested uptake are
equivalent (100-500μm). Disassociation rate constants were estimated for complexes of
CB congeners and dissolved organic carbon (DOC). CB-DOC complexes enhanced the
diffusive uptake rate constant for Tenax resin and, by inference, protozoan grazers.
In the second phase of this work, concentrations of surfactants, organic carbon and cells
were monitored over time in protozoan cultures. The effects of bacterial growth substrate
and protozoan species were examined. Surfactants increased during protozoan
exponential growth while total DOC concentrations decreased. Production of surface-active
material in ciliate cultures was significantly higher than in flagellate cultures, and
all protozoan cultures were higher than the bacterial control.
Common headspace vessels were then used to compare and contrast the affinity of
protozoan and bacterial culture filtrates (<0.2μm) for PCBs relative to a seawater control.
Affinities were normalized to bulk DOC and surfactant concentrations to determine
underlying relationships among these parameters. Values of equilibrium partition
coefficients (Koc) ranged from 1046 in Vineyard Sound seawater to 105.4 and 105.5 in
protist cultures, indicating that "grazer-enhanced" DOM was a better sorbent for PCBs
than DOM in bacterial controls and Vineyard Sound seawater.
Description
Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution February 2000
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Suggested Citation
Thesis: Kujawinski, Elizabeth B., "The effect of protozoan grazers on the cycling of polychlorinated biphenyls (PCBs) in marine systems", 2000-02, DOI:10.1575/1912/4104, https://hdl.handle.net/1912/4104Related items
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