Direct mass spectrometric measurement of gases in peat cores

Abstract

Dissolved gas concentrations (02, CH4, CO 2) in peat cores were monitored simultaneously using a fine (1.56 mm diameter) membrane inlet probe connected to a quadrupole mass spectrometer.This technique allows direct measurements at specific locations within the sample with minimal disturbance.Detailed gas profiles in completely waterlogged peat samples (hollows) and samples in which the water table was several cm below the vegetation surface (hummocks) were compared.The depth of the water table played a central role in the distribution of gases.In a hollow, oxygen was present (90/,~M) at the surface but was not detectable ( < 0.5 ~M) at depths greater than 2 cm.Concentrations of CH 4 and CO 2 increased from 6 and 300/xM respectively at the surface to maxima of 450 and 3900 #M at 13 cm depth.At a hummock, 0 2 and CO 2 were present above the water table but CH 4 was not detectable.CH 4 was measurable 2 cm below the water table.Both CH 4 and CO 2 concentrations increased with depth but maxima were not attained in the sampled cores.