Role of ammonia-oxidizing organisms in nutrient removal and methanogens in greenhouse gas emissions from natural, constructed wetlands and treatment ponds

Abstract

[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI AT AUTHOR'S REQUEST.] Ammonia oxidizing organisms play an important role in wetland water purification and nitrogen cycling. However, most treatment ponds or constructed wetlands are also an integral source of greenhouse gases such as methane (CH4) and nitrous oxide (N2O). Soil nitrification rates were determined and the seasonal and spatial distributions of ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB) in freshwater wetlands, constructed wetlands and stormwater treatment ponds by using specific primers targeting the amoA genes of AOA and AOB and real-time quantitative polymerase chain reaction (q-PCR) were investigated. The gene copies of AOA amoA were higher than those of AOB amoA by at least an order of magnitude in wetland soils and water in both summer and winter over a three-year study period in freshwater wetlands. AOA were more persistent and more abundant than AOB in the nutrient-depleted oligotrophic wetlands. In constructed wetlands, nitrification was correlated with a substantial increase of AOB population while the number of AOA in soils remained unchanged. These results suggest that nitrification is mainly driven by AOB in the constructed wetlands treating ammonia-laden wastewater. Ammonia-oxidizing archaea (AOA) and aceticlastic Methanosaeta appeared to be the dominant nitrifying and methanogenic organisms, respectively, in an oligotrophic duckweed treatment system. The results suggest that the oligotrophic ecological niche facilitates the growth of k-strategists such as AOA and Methanosaeta that may be responsible for nutrient removal and greenhouse gas emissions.