The Contribution of Anammox and Denitrification to Sediment N2 Production in a Surface Flow Constructed Wetland

This study used anaerobic slurry assays and intact core incubations to quantify potential rates of anammox (anaerobic ammonia oxidation) in sediments along the flow path of a surface flow constructed wetland receiving secondary treated sewage effluent. Anammox occurred at two of the four sites assayed with a maximum rate of 199.4 ± 18.7 μmol N·m−2·hr−1 (24% of total N2 production) at the discharge end of the wetland. Denitrification was the major producer of N2, with a maximum rate of 965.3 ± 122.8 μmol N·m−2.hr−1 at site 2. Oxygen was probably the key regulator of anammox activity within the studied CW. In addition to anammox, we found evidence that nitrifier-denitrification was potentially responsible for the production of N2O. Total production of N2O was 15.1% of the total gaseous N produced. Limitations to the methodology for quantifying anammox in CW's are outlined. This study demonstrated that denitrification is not the only pathway for gaseous production in constructed wetlands and that wetlands may be significant sources of greenhouse gases such as N2O.