Regulators of Methane Emission

The production and emission of methane is greatly affected by physical, chemical, and biological properties of soils. Some of these properties include organic matter content, nutrient composition, redox, pH, and salinity. Factors such as regional hydrology, temperature, substrate availability and quality, and salinity conditions affect not only the production of this trace gas but also its consumption by methanotrophs or its release from the soil to the atmosphere. 

Vegetation also plays a key role in the dynamics of methane production and emission. Generally the presence of macrophytes enhances emissions of methane. Emergent macrophytes supply important 

FIG U RE 16.4 Relationship between seasonal methane and water table position. (Adapted from Delaune et ah, 1983. Data summarized by Moore and Roulet, 1993.) 

Another environmental parameter that is important to methane emissions is soil temperatnre. Soil temperature affects the metabolic activity of microorganisms that prodnce substrates for inhibitors of methanogenesis as well as the methanogens themselves. Temperatnre is directly related to methanogenesis under field conditions (Schutz et al., 1990 Westermann, 1993). Methane emission rates generally parallel soil temperature levels. 

Methanogens require neutral pH conditions to function optimally. Methane prodnction occnrs only after a sequential reduction of other inorganic electron acceptors (e.g., Fe +, Mn +, SO ) it is produced at redox levels below which sulfate in soil is rednced. Methane prodnction is inversely related to sulfate concentration in wetland soils and sediments. High snlfate levels snch as those found in seawater can inhibit methane formation (DeLaune et al., 1983). 

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Vann C. D. and Megonigal J. P. (2003) Elevated CO2 and water depth regulation of methane emissions comparison of woody and non-woody wetland plant species. Biogeochemistry 63, 117-134. 

The third major release mechanism for the regulation of methane emission to the atmosphere is diffusion. However, this mode of transport does not appear to be as important as ebullition or vascular transport to net emissions. There appears to be two major reasons for this according to the literature reviewed. First, diffusion of gases into water is slower than into air by a factor of 10". ... 

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