Date of Award

Spring 2013

Document Type


Degree Name

Master of Science (MS)


Ocean & Earth Sciences


Ocean and Earth Sciences

Committee Director

Margaret Mulholland

Committee Member

Alexander Bochdansky

Committee Member

Andrew Gordon

Call Number for Print

Special Collections LD4331.O35 S373 2013


Coastal eutrophication resulting from nutrient over-enrichment plagues coastal waterways worldwide. In addition to dissolved inorganic N, many marine microbes, including phytoplankton, have the capacity to use certain dissolved organic nitrogen (DON) compounds. However, while we know that many specific DON compounds are labile, the bulk of the DON pool in nature is uncharacterized. The bioavailability of DON to estuarine microbes currently remains unclear.

It is becoming evident that natural phytoplankton assemblages in estuarine waters are capable of using both inorganic and organic N compounds for growth, both of which are present in anthropogenic point and non-point source discharges. Methods for assessing the bioavailability of diverse and mostly uncharacterized suite of organic N compounds are not yet established, but determination of natural community response to anthropogenic nutrient loading is critical for developing goals to reduce coastal eutrophication.

This study was designed to compare the bioavailability and impact of three different N sources to natural estuarine community assemblages. Anthropogenic N loads include nitrate and urea from fertilizers and other waste streams as well as other uncharacterized organic N, such as that found in treated wastewater effluents. Here, we amended natural estuarine communities with nitrate, urea, or concentrated WWTP effluent (referred to as C-WTEN in some tables) to compare the relative impacts of the different N compounds. Results from this study should be useful to managers as they target specific nutrient reductions.

I found that both inorganic and organic forms of nitrogen are bioavailable to the algal community and all forms of N tested were rapidly taken up within the first 4 hours after their addition to incubation bottles. Phytoplankton cell abundance increased within all N treatments and there was a shift in the composition of phytoplankton community structure based on whether organic or inorganic N was the dominant form of N provided. Both chlorophyll a concentrations and primary production levels in treatment bottles increased relative to control incubations for all N compounds tested. These results suggest that a reduction in total N loads, rather than specific N sources, is necessary to be protective of environmental quality and excess algal production.


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