Date Awarded


Document Type


Degree Name

Master of Arts (M.A.)


Virginia Institute of Marine Science


Kenneth L. Webb

Committee Member

Richard Wetzel

Committee Member

Howard Kator

Committee Member

Gene Silberhorn

Committee Member

Bruce Neilson


N2 fixation rates for several Virginia salt marshes were determined using in situ acetylene-reduction assays. A control and a chronically polluted oil marsh of the mesohaline Mobjack Bay area were sampled over a 1975-76 annual cycle. N2 fixation occurred in all transects which extended from upper mudflat to the Spartina patens zone. An isolated blue-green algal mat exhibited some of the highest N2 fixation rates. Intertidal sediment N2 fixation was patchy, both spatially and seasonally. However average rates (91.45 μg N/m2/h) compared to the estimated N requirement of the graminoid vegetation indicated a significant contribution to the N budget. Vegetation associated nitrogen fixation yielded higher average rates. N2 fixation rates for Wachapreague high salinity and Yorktown relic low salinity marshes were similar to the mesohaline marshes although blue-green algae fixation seemed to be more significant. The seasonal pattern of mesohaline marsh N2 fixation was positively related to temperature. Light-dark and anaerobic-aerobic experiments support the hypothesis that heterotrophic bacteria are the predominant N2 fixers and that availability of oxidizable substrates contribute to the seasonal pattern. Chronic oil treatment showed little effect on fixation rates with the possible exception of median tidal elevation sediments where summer rates were considerably higher than those of the control. This dissertation is from the Joint Program Degree from the College of William & Mary and University of Virginia and awarded by the University of Virginia.



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