Date Awarded


Document Type


Degree Name

Doctor of Philosophy (Ph.D.)


Virginia Institute of Marine Science


Howard Kator

Committee Member

Dick Wetzel


Section 1. Ecotoxicological effects of creosote contamination on benthic bacterial communities in the Elizabeth River, Virginia were investigated using both structural and functional microbial parameters. Results indicated that cell specific and total heterotrophic bacterial production parameters were depressed in a dose dependent manner with increasing sediment PAH concentrations. Toxicity effects upon production were modified by temporal trends associated with temperature as well as spatial sediment characteristics. of the parameters employed, the tritiated thymidine production assay was found to be the most sensitive for detection of ecotoxicological effects. Section 2. Bacterial abundance and production were examined during a destratification event in the lower James River, Virginia. Bacterial abundance, although significantly different between stations, did not change over the study. Bacterial production (&\sp3&H-Tdr incorporation) in surface waters was significantly less during the mixed period (187 &\mu&g C&\cdot&1&\sp{lcub}-1{rcub}\cdot& d&\sp{lcub}-1{rcub}&) compared to the most stratified state (324 &\mu&g C&\cdot&1&\sp{lcub}-1{rcub}\cdot& d&\sp{lcub}-1{rcub}&). Correlations between bacteria and chlorophyll were diminished during the mixed period. Total and flagellate specific grazing rates upon bacteria were reduced during the onset of destratification. Relationships between bacterial and nutrient parameters also indicated a strong influence of destratification. These results indicate that destratification changes trophic interactions within the microbial loop, which are not necessarily reflected in temporal patterns of bacterial abundance. Section 3. Bacterioplankton production, and ammonium assimilation and remineralization were examined between April and August 1988 in the lower York River, Va. Size fractionation enabled estimates of bacterial contribution (&&15 &\mu&m) towards ammonium cycling processes. Bacterial ammonium assimilation accounted for 19-95% of total dark ammonium assimilation, with station means of 46-48%. Station means of ammonium remineralization in the &<&1.6 &\mu&m treatment was 92, 48, and 38% of unfractionated values from lower to the upper river stations respectively. Regression statistics indicated that assimilation was best predicted by bacterial production. Remineralization was less well predicted by all variables. These results indicate the importance of bacteria in ammonium cycling can be greatly disproportionate to their biomass and production.



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