『Abstract
　Intact sediment cores from rivers of the Bothnian Bay (Baltic Sea) were studied for denitrification based on benthic fluxes of molecular nitrogen (N2) and nitrous oxide (N2O) in a temperature controlled continuous water flow laboratory microcosm under 10, 30, 100, and 300μM of ¹⁵N enriched nitrate (NO3^-, 〜98 at.％). Effluxes of both N2 and N2O from sediment to the overlying water increased with increasing NO3^- load. Although the ratio of N2O to N2 increased with increasing NO3^- load, it remained below 0.04, N2 always being the main product. At the NO3^- concentrations most frequently found in the studied river water (10-100μM), up to 8％ of the NO3^- was removed in denitrification, whereas with the highest concentration (300μM), the removal by denitrification was less than 2％. However, overall up to 42％ of the NO3^- was removed by mechanisms other than denitrification. As the microbial activity was simultaneously enhanced by the NO3^- load, shown as increased oxygen consumption and dissolved inorganic carbon efflux, it is likely that a majority of the NO3^- was assimilated by microbes during their growth. The ¹⁵N content in ammonium (NH4⁺) in the efflux was low, suggesting that reduction of NO3^- to NH4⁺ was not the reason for the NO3^- removal. This study provides the first published information on denitrification and N2O fluxes and their regulation by NO3^- load in eutrophic high latitude rivers.

Keywords: Stable isotopes; Eutrophication; NO3^- removal; N2O/N2 ratio; Bothnian Bay; River sediment』

Introduction
Material and methods
　Site description
　Sampling and experimental set-up
　Analyses of N2 and N2O
　NO3^- and NH4⁺ analyses
　Oxygen and pH measurements
　Data processing
　Statistical analyses
Results
　Denitrification and N2O effluxes
Discussion
　Denitrification rates as affected by NO3^- concentration
　N2O effluxes as affected by increasing the NO3^- load
　Nitrate removal and sediment metabolism
Conclusions
Acknowledgments
References