『Abstract
　In a microcosm ¹⁵N enrichment experiment we tested the effect of floating vegetation (Lemna sp.) and submerged vegetation (Elodea nutallii) on denitrification rates, and compared it to systems without macrophytes. Oxygen concentration, and thus photosynthesis, plays an important role in regulating denitrification rates and therefore the experiments were performed under dark as well as under light conditions. Denitrification rates differed widely between treatments, ranging from 2.8 to 20.9 μmol N m^-2 h^-1, and were strongly affected by the type of macrophytes present. These differences may be explained by the effects of macrophytes on oxygen conditions. highest denitrification rates were observed under a closed mat of floating macrophytes where oxygen concentrations were low. In the light, denitrification was inhibited by oxygen from photosynthesis by submerged macrophytes, and by benthic algae in the systems without macrophytes. however, in microcosms with floating vegetation there was no effect of light, as the closed mat of floating plants caused permanently dark conditions in the water column. Nitrate removal as dominated by plant uptake rather than denitrification, and did not differ between systems with submerged or floating plants.

Keywords: Denitrification; Ditches; Floating plants; macrophytes; Nitrogen』

Introduction
Methods
　Experimental setup
　Water quality analysis
　Denitrification measurements
　Nitrate removal
　Data analysis
Results
　Conditions in the microcosms
　Denitrification rates
　Water column dissolved oxygen
　Nitrate removal and phosphate release
Discussion
　Denitrification rates compared to natural systems
　Phosphorus release
Acknowledgments
Open access
References