Date of Award

Spring 2007

Document Type


Degree Name

Master of Science (MS)


Ocean & Earth Sciences


Ocean and Earth Sciences

Committee Director

Margaret Mulholland

Committee Member

Fred C. Dobbs

Committee Member

Andrew Gordon

Call Number for Print

Special Collections LD4331.O35 R634 2007


The most common methods for estimating bacterial productivity are [3H]-leucine and [3H]-thymidine incorporation. Uptake of these compounds has been attributed primarily to bacteria; however, because dissolved organic nitrogen may be an important N source for some phytoplankton, the use of these compounds to estimate bacterial productivity needs to be reexamined. In order to ascertain whether phytoplankton could compete with bacteria on relevant timescales and thereby bias bacterial productivity estimates in estuaries, I examined the ability of cultured phytoplankton and size-fractionated natural populations to take up leucine and thymidine in systems seasonally dominated by phytoplankton mixotrophs. In addition, grain density autoradiography was used to verify the incorporation of labeled substrates into individual phytoplankton cells. Results demonstrate that a variety of phytoplankton species can take up both leucine and thymidine at low concentrations during short incubations. The presence of silver grains in autoradiographs of phytoplankton cells after incubations of natural whole water samples with radio-labeled leucine and thymidine confirms that phytoplankton are capable of incorporating both substrates.


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