The Role of Denitrification in the Nitrogen Cycle of New England Salt Marshes

M. Robert Hamersley, Ph.D., 2002
Craig Taylor, Advisor

Salt marshes play important roles within the coastal environment as wildlife and fish habitat, aesthetic resources, and storm buffers. Salt marshes also have the capability of mitigating terrestrial nitrogen fluxes to sensitive coastal waters. Excessive nitrogen from wastewater disposal or fertilizers can cause eutrophication, with accompanying water column anoxia, loss of shellfish habitat, fish kills, and odors. Denitrification, a microbial process active in the sediments of salt marshes, converts nitrate to nitrogen gas, making it unavailable to algal uptake. I used direct measurements of nitrogen gas (N2) fluxes and a 15N stable isotope tracer to determine the contribution of denitrification to salt marsh sediment N cycling. I studied creekbottom denitrification by direct measurements of N2 fluxes in closed chambers against a low-N2 background. I undertook experiments and simulation modeling of sediment N2 fluxes in closed chambers to optimize the key experimental parameters of this approach. Direct measurements of O2, CO2, N2, and inorganic N fluxes from the sediments of a salt marsh tidal creek were made in order to examine the interaction of denitrification with the carbon, oxygen, and N cycles. Finally, a 15N-ammonium tracer was used to study competition between plants and nitrifying bacteria for remineralized ammonium.