The introduction of "new" nitrogen via nitrogen fixation may have a significant effect on nitrogen availability in estuaries and other partially enclosed aquatic systems. This thesis examines rates of nitrogen fixation associated with benthic microalgal communities in Florida Bay to determine the relative importance of this source as compared to external loads of nitrogen to the system.

Nitrogen fixation was measured using a number of experimental techniques to calibrate the use of the acetylene reduction assay and to determine the suitability of the N2:Ar comparison technique for measuring rates of nitrogen fixation.  Nitrogen fixation was found to be mediated by benthic microalgae at the surface of the sediments in Florida Bay and higher rates of fixation were measured in areas dominated by benthic microalgal mats.  Nitrogen fixation was highest in the relatively phosphorus-rich western basins and was stimulated by experimental phosphorus additions, suggesting that nitrogen fixation is partially phosphorus-limited.