Burns, J. A. UMCES Chesapeake Biological Lab, burns@cbl.umces.edu
Mellon, M. A. Rensselaer Polytechnic Institute, mellom@rpi.edu
Zehr, J. P. Rensselaer Polytechnic Institute, zehrj@rpi.edu
Paerl, H. W. Institute of Marine Sciences, University of North Carolina-MC, hans_paerl@unc.edu
Capone, D. G. UMCES Chesapeake Biological Lab, capone@cbl.umces.edu

 
NITROGEN FIXING PHYLOTYPES OF CHESAPEAKE BAY AND NEUSE RIVER ESTUARY SEDIMENTS: TRENDS IN PHYLOTYPE COMPOSITION CORRELATE WITH SEDIMENT CHARACTERISTICS
 
Sediments often exhibit low nitrogen fixation rates, despite the presence of elevated concentrations of inorganic nitrogen. The organisms which fix nitrogen in sediments have not been identified. Amplification of nifH genes with degenerate primers was used to determine the diversity of diazotrophs in two distinct sediment systems, anoxic muds of Chesapeake Bay and shallow surficial sediments of the Neuse River. Phylogenetic analysis revealed that sequences obtained from Mid Chesapeake Bay clustered closely with each other and with known anaerobic microorganisms, suggesting a low abundance of aerobic diazotrophs in these sediments. These sediments receive high organic loading and are highly reducing (Eh -261 mV). Sulfate reduction dominates at the surface, but methanogenesis becomes more important with depth. A thin (<1 cm) oxidized layer is present only in the spring. No archaeal nifH sequences were obtained from Chesapeake Bay. Sequences of nifH amplified from Neuse River surficial sediments included nif phylotypes related to sequences previously reported from marine mats and surficial sediments in Tomales Bay estuary. Differences in environmental site characteristic appear to select for different types of sediment diazotrophs, which is reflected in the phylogenetic composition of amplified nifH sequences.
 
Day: Thursday, Feb. 4
Time: Poster
Location: Sweeney Center
 
Code: CS63TH0954S