『Abstract
　Wetlands are often highly effective nitrogen (N) sinks. In the Lake Waco Wetland (LWW), near Waco, Texas, USA, nitrate (NO3^-) concentrations are reduced by more than 90％ in the first 500 m downstream of the inflow creating a distinct gradient in NO3^- concentration along the flow path of water. The relative importance of sediment denitrification (DNF) , dissimilatory NO3^- reduction to ammonium (DNRA), and N2 fixation were examined along the NO3^- concentration gradient in the LWW. “Potential DNRA” (hereafter potDNRA) was observed only in summer months and ranged from 1.3 to 33 μmol N m^-2 h^-1. Net N2 flux ranged from 184 (net denitrification) to -270 (net N2 fixation) μmol N m^-2 h^-1. Nitrogen fixation was variable, ranging from 0 to 426μmol N m^-2 h^-1, but high rates ranked among the highest reported for aquatic sediments. On average, summer potDNRA comprised only 5％ (±2％ SE) of total NO3^- loss through dissimilatory pathways, but was as high as 36％ at one site where potDNF was consistently low. Potential DNRA was higher in sediments with higher sediment oxygen demand (r² = 0.84), and was related to NO3^- concentration in overlaying water in one summer (r² = 0.81). sediments were a NO3^- sink and account for 50％ of wetland NO3^- removal (r² = 0.90). Sediments were an NH4⁺ source, but the wetland was often a net NH4⁺ sink. Although DNRA rates in freshwater wetlands may rival those observed in estuarine systems, the importance of DNRA in freshwater sediments appears to be minor relative to DNF. Furthermore, sediment N2 fixation can be extremely high when NO3^- in overlying water is consistently low. The data suggest that newly fixed N can support sustained N transformation processes such as DNF and DNRA when surface water inorganic N supply rates are low.

Keywords: DNRA; Coupled nitrification-denitrification; Sediment N transformation; N2 fixation; sediment nutrient flux 』

Introduction
Materials and methods
　Site description
　Sediment nutrient flux and N transformations
　Flow and wetland NO3^- and NH4⁺ flux estimates
Results
　Physical and chemical data at sediment coring sites
　Sediment nutrient fluxes
　Sediment N transformations and SOD
　Flow and wetland nutrient flow
Discussion
　potDNRA, potDNF, N2 fixation, and spatial variability along the NO3^- gradient
　potDNRA and coupled nitrification-DNF
　Sediment and wetland NO3^- removal
Conclusions
Acknowledgements
References