ACCUMULATION OF NITROUS-OXIDE IN AEROBIC GROUNDWATERS

N2O concentrations in the groundwaters collected in the Kanto District and Nagano Prefecture in Japan and five counties in New York State we re determined. These N2O data were obtained from the water samples fro m wells, springs and seepages from soils in forests and cropping field s. The N2O concentrations in all samples greatly exceeded those of atm ospheric equilibration. The average concentration of 690 nM N2O is one order of magnitude larger than that in deep ocean. All groundwaters o f the present study were aerobic with a high level of NO3-, but with t he absence of NO2- and NH4+, and with a very low level of dissolved or ganic carbon. These characteristics suggest that the nitrate respirati on in the aquifers is of little significance for the production of N2O . DELTAN2O/NO3- molar ratios in the groundwaters were between 10(-4) a nd 10(-2) (DELTA indicates the excess gas over that which would be in equilibrium). This supports the above view since the observed N2O yiel d agrees with that reported for the production during an ammonia oxida tion. If nitrification was indeed a major mechanism for the production of groundwater N2O, subsequent release of N2O from the aquifers that are polluted with nitrogen may deserve more close attention as a poten tial source of atmospheric N2O via diffusion and discharge.