Independent Effects of Temperature, Salinity, Ammonium Concentration and pH on Nitrification Rate of the Ariake Seawater Above Mud Sediment

The Ariake Sea located in the west parts of Kyushu Island is a semi-closed and macro-tidal shallow sea, and has the largest tidal flat in Japan. A large mud tidal flat with a productive ecosystem found along the western shoreline of the sea makes this area ideal as a major production site of nori (Porphyra yezoensis) in Japan. We determined the independent effect of temperature, salinity, ammonium concentration and pH on nitrification rates (NR) in the Ariake seawater above the mud sediment. The NR was determined by measuring accumulation of NO2-N production after adding sodium chlorate, an inhibitor of NO2-N to NO3-N oxidation. NRs were relatively high at 20-35 oC (optimum at 29.5 oC), but the rates were very low at 5, 10, and 40 oC. NRs increased sharply when increasing the salinity from 13 to 20 ppt, but it decreased drastically at salinity levels more than 35 ppt (optimum at 19 ppt). The relationship between ammonium concentration and NR showed a typical kinetic curve of enzymatic reaction with the maximum NR (Vmax) of 0.029 mM N.h-1 at 200 mM NH4-N (the half saturation constant (Ks) = 35 mM NH4-N). High NRs were determined at pH 7.5-8.0 (optimum pH 7.8). This is the first report on the independent effects of temperature, pH, salinity and NH4-N concentration on the NR of seawater, specifically the Ariake seawater

Nitrification Potential of Mud Sediment of the Ariake Sea Tidal Flat and the Individual Effect of Temperature, pH, Salinity and Ammonium Concentration on its Nitrification Rate

Abstract: The aims of this study were to know the nitrification potential of the mud sediment of the Ariake sea tidal flat, and to investigate the individual influence of environmental parameters such as temperature, pH, salinity and ammonium concentration on its nitrification rate. The Ariake Sea is a semi-closed shallow sea with macro-tidal and the largest tidal flat in Japan. Nitrification Potential Rate (NPR) and Nitrification Rate (NR) of the tidal flat mud sediment were determined by amending sodium chlorate to inhibit the oxidation of NO 2 -N to NO 3 -N. NPRs of the sediment were 91.4, 71.2 and 64.8 nmol N/g Dry Weight Sediment (DWS)/h at the depth of 0-3, 3-6 and 6-9 cm, respectively. NRs were relatively high in the temperatures range of 20-35 o C with the optimum temperature of 29.3 o C. Relatively high NRs were determined in the range of pHs 7.5-8 with the optimum pH 7.7. The optimum salinity for nitrification was 15 ppt. NRs increased drastically in the range of salinity 10 to 15 ppt, but it decreased sharply at 15 to 20 ppt. Relationship between ammonium concentration and NR resulted a hyperbolic Michaëlis-Menten type curve (R 2 = 0.98) with the maximum NR rate (Vmax) 32.5 nmol N/g DWS/h at NH 4 -N concentration 3,000 mM and the half saturation constant (Ks) 700 mM NH 4 -N. To our knowledge, this is the first report on nitrification of mud sediment of the Ariake sea tidal flat, and its optimal temperature, pH, salinity and NH 4 -N concentration as a single parameter

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

Abstract: 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, 2.278×10 3 -7.171×10 4 and 1.429×10 3 -7.171×10 4 cells/g sediment, were also found in silty clay loam sediment and sandy loam sediment, respectively. Correlations between pore water NH 4 -N concentration and NPR were found at sediment depths of 3-6 cm (r = 0.381; " = 0.05) and 6-9 cm (r = 0.786; " = 0.05). In these depths, the correlation also exhibited for AOB density and NPR (r = 0.595, " = 0.05 for 3-6 cm and r = 0.679, " = 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