Nitrifying bacteria mediate aerobic ammonia oxidation and urea hydrolysis within the Grand River

Ammonia oxidation is an important process for decreasing ammonia concentrations in wastewater-impacted rivers. Ammonia-oxidizing bacteria (AOB) and archaea (AOA) are responsible for ammonia oxidation, which is the first step of the nitrification process. Nitrification and urea hydrolysis were monitored in sediment and water column samples in the Grand River (Ontario), and nitrification inhibitors (allylthiourea and 2-phenyl-4, 4, 5, 5-tetramethylimidazoline-1-oxyl 3-oxide) helped identify the relative contributions of AOA and AOB to ammonia oxidation. Despite the presence of AOA, our results implicated AOB as the dominant contributors to ammonia oxidation, both directly and in association with urea hydrolysis.