Soil heterogeneity effects on O<inf>2</inf> distribution and CH<inf>4</inf> emissions from wetlands: In situ and mesocosm studies with planar O<inf>2</inf> optodes and membrane inlet mass spectrometry

The importance of soil heterogeneity for methane emission from a wetland soil is assessed by in situ point measurements of depth-specific O2 and CH4 concentrations and simultaneous soil CH4 fluxes at contrasting water levels. Profile measurements, and associated assumptions in their interpretation, were validated in a controlled mesocosm drainage and saturation experiment applying planar O2 optodes and membrane inlet mass spectrometry. Results show that peat soil is heterogeneous containing dynamic macropore systems created by both macrofauna and flora, which facilitate preferential flow of water, O2 and CH4 and vary temporally with changes in the moisture regime. The O2 content above the water table after drainage varied horizontally from 0 to 100% air saturation within few mm. Oxic zones were observed below the water level and anoxic zones were observed in layers above the water level in periods up to days after changes in the water level. This study shows that although water table position is a competent proxy of soil CH4 fluxes at larger spatio-temporal scales, it becomes inadequate at higher spatial resolution, i.e. at the scale of the soil pedon and below. High resolution O2 measurements using planar O2 optodes have great potential to enhance our understanding of the effect of the water table position on O2 dynamics on scales of several cm to mm in wetland soils. © 2010 Elsevier Ltd

Linking soil O<inf>2</inf>, CO<inf>2</inf>, and CH<inf>4</inf> concentrations in a wetland soil: Implications for CO<inf>2</inf> and CH <inf>4</inf> fluxes

Oxygen (O2) availability and diffusivity in wetlands are controlling factors for the production and consumption of both carbon dioxide (CO2) and methane (CH4) in the subsoil and thereby potential emission of these greenhouse gases to the atmosphere. To examine the linkage between high-resolution spatiotemporal trends in O2 availability and CH4/CO2 dynamics in situ, we compare high-resolution subsurface O2 concentrations, weekly measurements of subsurface CH4/CO2 concentrations and near continuous flux measurements of CO2 and CH4. Detailed 2-D distributions of O2 concentrations and depth-profiles of CO2 and CH 4 were measured in the laboratory during flooding of soil columns using a combination of planar O2 optodes and membrane inlet mass spectrometry. Microsensors were used to assess apparent diffusivity under both field and laboratory conditions. Gas concentration profiles were analyzed with a diffusion-reaction model for quantifying production/consumption profiles of O2, CO2, and CH4. In drained conditions, O 2 consumption exceeded CO2 production, indicating CO 2 dissolution in the remaining water-filled pockets. CH4 emissions were negligible when the oxic zone was >40 cm and CH4 was presumably consumed below the depth of detectable O2. In flooded conditions, O2 was transported by other mechanisms than simple diffusion in the aqueous phase. This work demonstrates the importance of changes in near-surface apparent diffusivity, microscale O2 dynamics, as well as gas transport via aerenchymous plants tissue on soil gas dynamics and greenhouse gas emissions following marked changes in water level. © 2011 American Chemical Society

Metals in some dominant vascular plants, mosses, lichens, algae, and the biological soil crust in various types of terrestrial tundra, SW Spitsbergen, Norway

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