Preliminary Studies on Gross Nitrification, Denitrification and Respiratory Rates in Sediments from a Typical Coastal Wetland, Chongming East Intertidal, Using a Method of BaPS

Drying and re-flooding in coastal wetlands physically response to the periodic semi-lunar and diurnal tides, together with the rising and leaching of salts. This substantially complicates nitrogen transformation in sediments. Sediment and water samples are taken from Chongming east intertidal flat, a typical coastal wetland in China, to investigate gross nitrification, denitrification and respiratory rates under three simulated processes of drying and rewetting, using a method of barometric process separation (BaPS). When moisture of sediment decreases to 30% during drying period, nitrification, denitrification and respiratory rates reach the maximum of 2249, 4149 μg N·kg^-1SDW·h^-1 and 3948 μg C·kg^-1SDW·h^-1, respectively. After then, the rates decrease linearly with the decreasing moisture. During the cycles of semi-lunar tide, the highest nitrification and denitrification rates occur at moisture of 30-35% with a mean of 2809±925 and 4280±115 μg N·kg^-1SDW·h^-1, respectively. In contrast, the respiratory rates reach the highest at 20-40%, varying between 3165-6677 μg C·kg^-1SDW·h^-1. In addition, it is found that BaPS system does not smoothly work when moisture of sediment is above 40%.