Nitrous oxide emissions from coastal waters in Tokyo Bay

The distribution, source and atmospheric flux of nitrous oxide (N2O) in seawater in Tokyo Bay were investigated from May to October 1994 to evaluate this area as an N2O source to the atmosphere. N2O was measured from seawater at 23 sampling stations (n=178). Nitrate (NO3−), nitrite (NO2−), ammonium (NH4+), oxygen (O2), water temperature and salinity were also determined. N2O was supersaturated in all surface seawater; the surface N2O saturation ranged from 116 to 1630%. Both the high concentration of surface N2O in the low salinity region and absence of significant spatial deviation in the distribution of N2O with season suggested that the main source of N2O was input of fresh water; discharge of treated sewage waters containing N2O in the bay area is probably the main source of the observed high concentrations of N2O in seawater there.