Short-Term Dynamics of NH4-N Affected by Water Discharged from a Reservoir of Reclaimed Land into Isahaya Bay, Kyushu, Japan

We conducted a high-resolution field survey at nine sampling stations from September 18 to 19, 2012, to evaluate the short-term dynamics of NH4-N affected by the discharge of high-turbidity water into Isahaya Bay, Japan, from a reservoir of reclaimed land. In front of the north gate, the concentration of particulate nitrogen reached 100 μmol·L-1 just after the discharge. In contrast, the NH4-N concentration tended to vary with tidal height and reached 9.3 μmol·L-1. The mean rate of increase of NH4-N measured in front of the north gate was estimated to be 1.8 mmol N·m-2·h-1 on the basis of its time series variation. Thus, NH4-N regenerated from the discharged organic matter would be one of the nutrient sources for the red tide in this bay.