Denitrification and anammox occur widely in aquatic ecosystems serving vital roles in nitrogen pollution removal. However, small waterbodies are sensitive to external influences; stormwater runoff carrying nutrients and oxygen, flows into waterbodies resulting in a disruption of geochemical and microbial processes. Nonetheless, little is known about how these short-term external inputs affect the microbial processes of nitrogen removal in small waterbodies. To investigate the effects of NO3-, NH4+, dissolved oxygen (DO) and organic C on microbial nitrogen removal in pond sediments, regulation experiments have been conducted using slurry incubation experiments and 15N tracer techniques in this study. It was demonstrated the addition of NO3- (50 to 800 μmol L-1) significantly promoted denitrification rates, as expected by Michaelis-Menten kinetics. Ponds with higher NO3- concentrations in the overlying water responded more greatly to NO3- additions. Moreover, N2O production was also promoted by such an addition of NO3-. Denitrification was significantly inhibited by the elevation of DO concentration from 0 to 2 mg L-1, after which no significant increase in inhibition was observed. Denitrification rates increased when organic C was introduced. Due to the abundant NH4+ in pond sediments, the addition demonstrated little influence on nitrogen removal. Moreover, anammox rates showed no significant changes to any amendment.
Keywords: dissolved oxygen; external impact; nitrate; nitrogen removal; nitrous oxide; regulation experiments.