An experimental study on effects of submersed macrophytes on nitrification and denitrification in ammonium‐rich aquatic systems

Abstract

We have examined the role of microbial communities on the surface of submersed macrophytes and in the underlying sediment for nitrification and denitrification in light and dark in NH4+‐enriched microcosm systems using isotope pairing and dilution techniques. Potamogeton pectinatus L. and intact sediment cores were collected in a shallow reservoir receiving treated municipal wastewater and containing dense submersed vegetation. Chambers containing P. pectinatus shoots, sediment, or both P. pectinatus shoots and sediment were exposed to 6 h of darkness, 6 h of light, and 6 h of darkness. 14NH4+ and 15NO3− were added at ambient concentrations of 15 and 5 mg N liter−1, respectively. NH4+ was primarily nitrified in the epiphytic microbial communities, and NO3− was denitrified in the underlying sediment. In chambers containing macrophytes, there was a net production of O2 and NO3− in light and a net consumption in dark, and nitrification was higher in light than in dark. In chambers with only sediment, there was always a net consumption of NO3−, and nitrification was similar in light and dark. The results show that submersed macrophytes can be important for the N metabolism in NH4+‐ rich freshwaters (e.g., wastewater treatment systems) by stimulating nitrification through providing surfaces for attached nitrifying bacteria and possibly also through diurnal changes in the water chemistry.