Nitrogen Fixation in Microphytobenthos-Dominated Zones of Florida Bay
Eric D. Nagel, Jeffrey C. Cornwell, W. Michael Kemp, Michael S. Owens
University of Maryland Center for Environmental Science, Horn Point Laboratory
Cambridge, MD
Nitrogen cycling in Florida Bay is composed of a number of internal and external
biogeochemical processes that govern the fate and availability of nitrogen within the
system. Many recent studies have focused on the loading of nitrogen into Florida Bay
from external sources in the development of a system-wide nitrogen cycling model.
However, compared to external processes little is known about internal processes that
also may introduce nitrogen to the system on more immediate spatial scales. Nitrogen
fixation is one of these potentially important internal sources of bioavailable nitrogen to
benthic environments in the basins of Florida Bay. Benthic systems in Florida Bay are
generally dominated by dense stands of seagrass. However, with the recent advent of
large areas of seagrass die-back, zones dominated by microphytobenthos have become
more numerous and perhaps, of greater influence to the overall nitrogen cycling patterns
in Florida Bay. In this research project we seek to measure rates of nitrogen fixation,
create an annual profile of nitrogen fixation, and investigate abiotic controls on fixation
in microphytobenthos-dominated zones at sites located throughout Florida Bay. Here we
present measurements of nitrogen fixation rates in multiple basins as determined by the
acetylene reduction and 15N techniques. Preliminary results show fixation rates of 1-10
mol N2-N * m-2 * hr-1 which is of the same magnitude to external inputs from the
atmosphere (through precipitation) and terrestrial sources.
Nagel, Eric, University of Maryland Center for Environmental Science – Horn Point
Laboratory, 2020 Horns Point Rd., Cambridge, MD 21613, Phone (410) 221-8209, FAX
(410) 221-8490, enagel@hpl.umces.edu, Question # 2