Nitrification Potential Rate of Different Sediment Types of the Ariake Sea Tidal Flat in Summer and Autumn

The purpose of this research was to investigate the nitrification potential in different sediment types in the Ariake Sea tidal flat. The Ariake Sea, a semi-closed shallow sea with macro-tidal and a large tidal flat, is located in the west part of Kyushu Island, Japan. Different kinds of sediment develop in the different parts of its tidal flat. We analyzed and classified the sediment textures, physico-chemical properties of sediment pore water, Ammonium-Oxidizing Bacteria (AOB) density, and determined their Nitrification Potential Rate (NPR). The sediment textures from intertidal zone were classified to be silty clay loam, sandy loam and loamy sand, and sediment from a sub-tidal zone to be sandy loam for 6 cm upper most sediment, and loamy sand for 6-9 cm sediment depth. The highest NPR was found in silty clay loam sediment (12.072-59.102 nmol N/g Dry Weight Sediment (DWS)/h) followed by sandy loam (7.29-21.056 nmol N/g DWS/ h), and the other sediment textures. The high AOB densities, 2.278×103-7.171×104 and 1.429×103-7.171×104 cells/g sediment, were also found in silty clay loam sediment and sandy loam sediment, respectively. Correlations between pore water NH4- N concentration and NPR were found at sediment depths of 3-6 cm (r = 0.381; α = 0.05) and 6-9 cm (r = 0.786; α = 0.05). In these depths, the correlation also exhibited for AOB density and NPR (r = 0.595, α = 0.05 for 3-6 cm and r = 0.679, α = 0.05 for 6-9 cm depths). However, these two correlations was not approved for 3 cm upper most sediment. It is the first report on nitrification potential in the different kinds of sediment of the Ariake Sea which improve our understanding of the nitrification in this area.