Potential nitrification and cation exchange on litter of emergent, freshwater macrophytes

1. Macrophyte litter and dead stems can comprise the dominant surface area in freshwater wetlands and in the littoral of lakes, providing a habitat for microorganisms including nitrifiers, and also binding sites for NH sub(4) super(+). 2. We have determined the potential oxidation of NH sub(4) super(+) and NO sub(2) super(-) by attached nitrifying bacteria and cation exchange capacity (CEC) on litter of Scirpus sylvaticus L., Carex rostrata Stokes, Equisetum fluviatile L. and Typha latifolia L. sampled in a constructed surface-flow wetland. In addition, a bioassay was developed to investigate the effects of the macrophyte litter on the nitrification process. 3. NH sub(4) super(+) oxidation and NO sub(2) super(-) oxidation of the attached nitrifying bacteria followed the same pattern, with higher rates on S. sylvaticus and C. rostrata litter than on litter of E. fluviatile and T. latifolia. The nitrification on the litter was not correlated to its CEC. S. sylvaticus, C. rostrata and T. latifolia litter had similar CEC. E. fluviatile had lower CEC than the others. 4. The bioassay shows that litter of emergent freshwater macrophytes can restrain bacterial NH sub(4) super(+) oxidation. 5. This study has shown that the activity of attached nitrifying bacteria differs greatly between litter of different emergent macrophytes, suggesting that the spatial distribution of nitrification activity within wetland ecosystems is related to the species composition of the emergent vegetation. In addition, it indicates that compounds released from the emergent macrophytes during their decomposition may have negative effects on the nitrification within macrophyte beds in wetlands and littoral zones.