『Abstract
　Urban streams often contain elevated concentrations of nitrogen (N) which can be amplified in systems receiving effluent from wastewater treatment plants (WWTP). In this study, we evaluated the importance of denitrification in a stream draining urban Greensboro, NC, USA, using two approaches: (1) natural abundance of ¹⁵N-NO3^- in conjunction with background NO3^--N concentrations along a 7 km transect downstream of a WWTP; and (2) C2H2 block experiments at three sites and at three habitat types within each site. Overall lack of a longitudinal pattern of δ¹⁵N-NO3^- and NO3^--N, combined with high concentrations of NO3^--N suggested that other factors were controlling NO3^--N flux in the study transect. However, denitrification did appear to be significant along one portion of the transect. C2H2 block experiments showed that denitrification rates were much higher downstream of the WWTP compared to upstream, and showed that denitrification rates were highest in erosional and depositional areas downstream of the WWTP and in erosional areas upstream of the plant. Thus, the combination of the two methods for evaluating denitrification provided more insight into the spatial dynamics of denitrification activity than either approach alone. Denitrification appeared to be a significant sink for NO3^--N upstream of the WWTP, but not downstream. Approximately 46％ of the total NO3^--N load was removed via denitrification in the upstream, urban section of the stream, while only 2.3％ of NO3^--N was lost downstream of the plant. This result suggests that controlling NO3^--N loading from the plant could result in considerable improvement of downstream water quality.

Keywords: Denitrification; Nitrogen; δ¹⁵N-NO3^-; Urban stream; Wastewater』

Introduction
Materials and methods
　Study sites
　Field procedures
　Laboratory procedures
　Statistical analyses
Results
　Natural abundance of δ¹⁵N-NO3^-
　Physical and chemical parameters from sediment core sampling sites
　Denitrification rates between sites
　Denitrification rates between habitat types
Discussion
　Natural abundance of δ¹⁵N-NO3^-
　Spatial variability in denitrification rates (C2H2 Reduction)
　Proportion of NO3-N loss to denitrification
Conclusions
References