Mass spectrometric monitoring of gases (CO2, CH4, O-2) in a mesotrophic peat core from Kopparas Mire, Sweden

Membrane inlet mass spectrometry was used to monitor dissolved gas concentrations (CO2, CH4 and O2) in a mesotrophic peat core from Kopparås, Sweden. A comparison of depth profiles (down to 22 cm) with an ombrotrophic peat core (Ellergower, SW Scotland) investigated previously, revealed major differences in gas concentrations. Thus methane reached concentrations more than twice as high (800 μM) at depths greater than 12 cm in the Kopparås core. As shown previously, the primary determinant of the depth of the oxic zone is the level of the water table. Whereas in the Scottish cores, mass spectrometric detectability of O2 was confined to the first 3 cm below this level, in the Swedish core penetration of O2 was greater (7 cm). CO2 profiles were similar in cores from both locations. A thick layer of Sphagnum mosses dominated the plant cover of the Swedish peat core. A poorly developed deep root system, as distinct from that of the vascular plant cover in Scottish cores, diminished gas exchange rates, and presumably aerobic methane oxidation at depth around roots. These characteristics may contribute to the development of discontinuities in gas profiles at depths greater 15 cm as upward gas transport is established predominantly by diffusion and/or ebullition in the Swedish core. 3 Monitoring gas concentrations at the peat surface and at 2 cm depth after changing water tables showed a delayed response of approximately 4 days as a result of the high water content and moisture-regulating capacity of mosses. 4 Recovery processes at 2 cm depth after raising the water table revealed final production rates of dissolved CO2 and CH4 in the peat pore water between 0.8 and 4.4 μmol h−1 L−1 and between 0.1 and 1.7 μmol h−1 L−1, respectively. Higher production rates were found during the day, indicating a diurnal rhythm due to plant photosynthetic activity even at the low values of photosynthetically active radiation (PAR: 110 μmol s−1 m−2) used in the experimental set-up. 5 In the water-logged mesotrophic Kopparås core changes of dissolved gas concentrations (DGC) at 3 and 14 cm depth were surface temperature-dependent rather than light dependent. This suggests that changes of air temperature alters the covering vegetation to increase the conductivity for dissolved gases through vascular plants and to facilitate gas transport by diffusion and/or ebullition.