Denitrification in intact subsoil cores
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Intact, unamended subsoil cores taken from two contrasting field sites were incubated in the laboratory at 12 °C under aerobic (21% O2) and anaerobic (1.1–5.5% O2) conditions. Denitrification of 15N-NO3– diffusing into the cores across a semi-permeable membrane was estimated by: (1) direct observation of 15N-labelled 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– is not limited by diffusion) was estimated using a finite-difference approximation to a diffusion reaction equation based on comparison of time and depth profiles of NO3– and Br– in the incubated cores. Potentials between 0.2 and 2.5 mg N kg–1 day–1 were obtained under low O2 and natural C concentrations. These results indicate the potential for denitrification in glacial till subsoils to reduce NO3– leaching to ground or surface waters to levels unlikely to result in a pollution hazard. The major product of NO3– 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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