Denitrification and Anammox and Feammox in the Yinchuan Yellow River wetland

Denitrification, anaerobic ammonium oxidation (Anammox), and ferric iron reduction coupled with anaerobic ammonium oxidation (Feammox) are the nitrogen removal pathways in natural ecosystems. In this study, the differences between these three nitrogen removal pathways in a Phragmites australis covered site (LW), artificial grassland covered site (CD), poplar covered site (YD), and topsoil tillage after harvesting reed site (GD) in the Yinchuan Yellow River wetland were investigated using isotope tracing, metagenome, and quantitative polymerase chain reaction (Q-PCR) techniques. No³⁰ N₂ accumulation was detected in¹⁵ NH₄⁺ addition incubations, indicating that Feammox was weak in all sites, which is consistent with a low abundance of the Feammox functional bacteria Acidimiprobiaceae sp. A6. The denitrification rates were 0.36 (LW), 0.5 (CD), 0.76 (YD) and 0.12 (GD) mg N/kg/day. The Anammox rates were 0.18 (LW) and 0.26 (GD) mg N/kg/day; other sites did not detect Anammox rate. Denitri-fication was the dominant pathway except for the CD site. The YD site had the highest abundance of denitrification genes, which was consistent with the denitrification rate.