Driving force of tidal pulses on denitrifiers-dominated nitrogen oxide emissions from intertidal wetland sediments

Intertidal wetland sediments are an important source of atmospheric nitrogen oxides (NO_x), but their contribution to the global NO_x budget remains unclear. In this work, we conducted year-round and diurnal observations in the intertidal wetland of Jiaozhou Bay to explore their regional source-sink patterns and influence factors on NO_x emissions (initially in the form of nitric oxide) and used a dynamic soil reactor to further extend the mechanisms underlying the tidal pulse of nitric oxide (NO) observed in our investigations. The annual fluxes of NO_x in the vegetated wetland were significantly higher than those in the wetland without vegetation. Their annual variations could be attributed to changes in temperature and the amount of organic carbon in the sediment, which was derived from vegetated plants and promoted the carbon-nitrogen cycle. Anaerobic denitrifiers had advantages in the intertidal wetland sediment and accounted for the major NO production (63.8 %) but were still limited by nitrite and nitrate concentrations in the sediment. Moreover, the tidal pulse was likely a primary driver of NO_x emissions from intertidal wetlands over short periods, which was not considered in previous investigations. The annual NO exchange flux considering the tide pulse contribution (8.93 ± 1.72 × 10^-2 kg N ha^-1 yr^-1) was significantly higher than that of the non-pulse period (4.14 ± 1.13 × 10^-2 kg N ha^-1 yr^-1) in our modeling result for the fluxes over the last decade. Therefore, the current measurement of NO_x fluxes underestimated the actual gas emission without considering the tidal pulse.