Stable Nitrogen Isotope Ratios as a Tracer of Bacterial Nitrogen Sources in Estuarine and Coastal Waters

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Newly developed nucleic acid probes will be used to study nitrogen cycling between dissolved substrate pools and bacteriain estuarine, coastal and open ocean waters. It is anticipatedthat the implementation of these techniques will provide and approach to examine the relative importance of bacterial nitrogen sources where multiple sources with varying nutritional values are available. The focus of this research will be: 1) to complete the adaptation of a nucleic acid isolation/isotope measurement technique, which was used to trace bacterial carbon sources in estuarine waters, to one that will trace bacterial nitrogen sources in eutrophic and oligotrophic waters, 2) to continue development and field testing of a method to measure stable nitrogen isotopes in dissolved organic matter, and 3) to compare the isotopic discrimination between bacteria (isolated as nucleic acids) and nitrogen sources in eutrophic and oligotrophic waters. Field work will be conducted on a transect from the Trinity River, Texas to the mouth of Galveston Bay out additional stations along the standard transect from Galveston Bay out to the 2000 m isobath in the Gulf of Mexico.