The effects of semi-lunar spring and neap tidal change on nitrification, denitrification and N2O vertical distribution in the intertidal sediments of the Yangtze estuary, China

To explore the influences of semi-lunar spring and neap tidal changes on nitrogen cycling in intertidal sediments, a comparative study among waterlogged, desiccated and reflooded systems was carried out in August 2005 and February 2006 by analyzing nitrification, denitrification and N2O depth profiles in the intertidal flats of the Yangtze estuary. Laboratory experiments showed that alternating emersion and inundation resulted in the significant changes in nitrification and denitrification rates in the intertidal sediment systems. Due to the desiccation-related effects, lowest nitrification and denitrification rates were observed in the desiccated sediment cores. Highest nitrification and denitrification rates were however detected in the waterlogged and reflooded systems, respectively. It is hypothesized that the highest nitrification rates in the waterlogged sediments were mainly attributed to higher nitrifier numbers and NH4+ being more available, whereas the availability of NO3− might dominate denitrification in the reflooded sediments. In addition, the highest N2O concentrations were detected in the reflooded sediment cores, and the lowest found in the dried sediment cores. It was also shown that N2O in the intertidal sediments was mainly from nitrification under the desiccated condition. In contrast, N2O in the intertidal sediments was produced mainly via denitrification under the waterlogged and reflooded conditions. It is therefore concluded that the semi-lunar tidal cycle has a significant influence on nitrification, denitrification and N2O production in the intertidal sediment systems.