Nitrate Addition Increases the Activity of Microbial Nitrogen Removal in Freshwater Sediment

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 NO(3)(−), NH(4)(+), dissolved oxygen (DO) and organic C on microbial nitrogen removal in pond sediments, regulation experiments have been conducted using slurry incubation experiments and (15)N tracer techniques in this study. It was demonstrated the addition of NO(3)(−) (50 to 800 μmol L(−1)) significantly promoted denitrification rates, as expected by Michaelis-Menten kinetics. Ponds with higher NO(3)(−) concentrations in the overlying water responded more greatly to NO(3)(−) additions. Moreover, N(2)O production was also promoted by such an addition of NO(3)(−). 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 NH(4)(+) in pond sediments, the addition demonstrated little influence on nitrogen removal. Moreover, anammox rates showed no significant changes to any amendment.