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

Eriksson, Peder G., Stefan E. B. Weisner

Limnol. Oceanogr., 44(8), 1999, 1993-1999 | DOI: 10.4319/lo.1999.44.8.1993

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.

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