Denitrification and degassing in groundwater estimated from dissolved dinitrogen and argon

The groundwater concentrations of dinitrogen (N-2) and argon (Ar) were measured in a transect of a Danish riparian wetland in order to estimate N-2 production from denitrification, the concentration of Ar being used as an internal tracer for degassing, Dissolved N-2 increased by 135 mu M N-2-N. Simple calculations incorporating the decrease in groundwater dissolved Ar and the partial pressure of N-2 revealed that 376 mu M N-2-N was degassed along the transect. Total denitrification thus amounted to 511 mu M N-2-N, correlating well with the measured NO3- reduction of 503 mu M NO3-N. The total partial pressures of dissolved gases (N-2, O-2, Ar, and CO2) exceeded the hydrostatic pressure, thus confirming that degassing was a plausible mechanism for loss of dissolved gases in this riparian wetland, This study provides strong evidence that losses of dissolved Ar along a transect parallel to groundwater flow can be used to assess the amount of dissolved N-2 degassed and thereby permit estimates of N-2 production under conditions without conservation of gases within the groundwater system. (C) 1998 Elsevier Science B.V. All rights reserved.