Nitrous Oxide Dissolved in Soil Solution: An Insignificant Pathway of Nitrogen Loss From a Southeastern Hardwood Forest

Nitrous oxide is soluble and can accumulate in soil solution when gaseous diffusion is restricted. The importance of N losses via degassing of N2O from groundwater entering surface streams is unknown. Measurements of N2O in soil solution revealed patterns of seasonal and spatial variation that were consistent with ecosystem regulation of denitrification. The highest concentrations were observed in the riparian zone in May, when soil NOf, temperature, and moisture were conducive for denitrification. At each of the other sample dates and sites, at least one of these factors appeared to prevent significant N2O accumulation in soil solution. Extrapolation of the highest observed N2O concentrations to an annual basis corresponded to a loss of only 56 g N ha ~' yr ~'. Denitrification in the riparian zone may be an important fate of N in this hardwood forest, but N2O in soil solution does not appear to be a significant pathway of N loss. This site might be expected to produce N2O at higher rates than most hardwood forests, but extrapolation of the highest calculated losses from soil solution over the global area occupied by hardwood forest indicates that this source of N2O is insignificant for global atmospheric budgets.