The effect of temperature on methane dynamics in soil and peat cores: Calculations from membrane inlet mass spectrometry

Abstract

Methanogenesis and methane oxidation, fundamental microbial processes in the global carbon cycle, are mediated by numerous factors in terrestrial soil and wetland ecosystems. Accurate quantification of CH4 and CO 2 concentrations in soils and wetlands is now possible using membrane inlet mass spectrometry. Below-ground production and headspace exchange of O2, CO2 and CH4 were monitored in microcosms from an upland Soil (Scotland) and three different peat bog systems (Sweden, Iceland and Scotland) by membrane inlet mass spectrometry. A comparison of cores from the different locations revealed that temperature, soil structure, plant cover and water table level are associated with the regulation of the depth of oxygen available for methanotrophic processes in the oxic zone and therefore gas emission rates. In aerobic soil cores, all the methane produced in anaerobic sites is oxidised rather than being emitted from the soil surface. In peat cores, molar CH4:CO2-ratios of around 1:10 indicate the boundary between the oxic and the anoxic zones. Changes in dissolved gas concentrations with depth and especially the molar CH4:CO 2-ratios are discussed. We also demonstrate that inconsistencies in dissolved gas profiles, along with higher localized molar CH4:CO 2-ratios, indicate bubble formation at depths greater than 10 cm; gas emission by ebullition was promoted at these sites. Increase in temperature had a particularly strong effect upon gas dynamics in soil and peat cores. Gas solubilities were reduced and elevated CO2 and CH4 emission rates were observed potentially due to increased microbial activity.