『Abstract
　Nitrogen (N) dynamics at the sediment-water interface were examined in four regions of Florida Bay to provide mechanistic information on the fate and effects of increased N inputs to shallow, subtropical, coastal environments. Dissimilatory nitrate (NO3^-) reduction to ammonium (DNRA) was hypothesized to be a significant mechanism retaining bioreactive N in this warm, saline coastal ecosystem. Nitrogen dynamics, phosphorus (P) fluxes, and sediment oxygen demand (SOD) were measured in north-central (Rankin Key; eutrophic), north-eastern (Duck Key; high N to P seston ratios), north-western (Murray Key; low N to P ratios), and central (Rabbit Key; typical central site) Florida Bay in August 2004, January 2005, and November 2006. Site water was passed over intact sediment cores, and changes in oxygen (O2), phosphate (o-PO4^3-), ammonium (NH4⁺), NO3^-, nitrite (NO2^-), and N2 concentrations were measured, without and with addition of excess ¹⁵NO3^- or ¹⁵NH4⁺ to inflow water. These incubations provided estimates of SOD, nutrient fluxes, N2 production, and potential DNRA rates. Denitrification rates were lowest in summer, when SOD was highest. DNRA rates and NH4⁺ fluxes were high in summer at the eutrophic Rankin site, when denitrification rates were low and almost no N2 came from added ¹⁵NO3^-. Highest ¹⁵NH4⁺ accumulation, resulting from DNRA, occurred at Rabbit Key during a picocyanobacteria bloom in November. ¹⁵NH4⁺ accumulation rates among the stations correlated with SOD in August and January, but not in November during the algal bloom. These mechanistic results help explain why bioreactive N supply rates are sometimes high in Florida Bay and why denitrification efficiency may decrease with increased NO3^- inputs in sub-tropical coastal environments.

Keywords: Florida Bay; Nitrogen transformations; DNRA; Denitrification; Subtropical/tropical ecosystems』

Introduction
Experimental sites and methods
Results
　Station characteristics and nutrient concentrations in August 2004, January 2005, and November 2006
　Nutrient fluxes
　N2 production rates, NH4⁺ fluxes, and potential DNRA rates
　Relative importance of DNRA vs. denitrification to the fate of NO3^-
　Potential anammox rates in January and November
　Relationship of N2 flux and potential DNRA rates to total sediment O2 demand
Discussion
　Conceptual summary of N dynamics in Florida Bay
Acknowledgments
References