Intact, unamended subsoil cores taken from two contrasting field sites were incubated in the laboratory at 12 7C under aerobic (21% O2) and anaerobic (1.15.5% O2) conditions. Denitrification of 15N-NO3 P diffusing into the cores across a semi-permeable membrane was estimated by: (1) direct observation of 15Nlabelled N2 and N2O, and (2) mass balance following sectioning at the end of the experiment. The in situ denitrification potential (rates where the supply of NO3 P is not limited by diffusion) was estimated using a finitedifference approximation to a diffusion reaction equation based on comparison of time and depth profiles of NO3 P and BrP in the incubated cores. Potentials between 0.2 and 2.5 mg N kgP1 dayP1 were obtained under low O2 and natural C concentrations. These results indicate the potential for denitrification in glacial till subsoils to reduce NO3 P leaching to ground or surface waters to levels unlikely to result in a pollution hazard. The major product of NO3 P reduction in these subsoils was observed to be N2, rather than the greenhouse gas and catalyst of stratospheric O3 removal, N2O.
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