Dissolved methane dynamics in a subarctic peatland

Abstract: Popular science: Methane (CH₄) is a colorless, odorless, tasteless gas that can trap heat in the atmosphere. It is believed to be a powerful greenhouse gas. The concentration of CH₄ in the atmosphere is much lower than that of CO₂, but it is more effectively trapping infrared radiation and therefore contributes significantly to the “greenhouse effect” of the Earth. Northern peatland is a dominating natural source of CH₄. It provides waterlogged, anoxic and cool conditions, these conditions were in favor of methane production. Dissolved methane is CH₄ gas that dissolves in water, under certain conditions it can bubble up from underground sources through fens and bogs and release into the atmosphere, thus dissolved CH₄ is considered as one of potential CH₄ emissions. Through investigating the seasonal changes of dissolved CH₄ we may better understand the processes affecting seasonal CH₄ emission in northern peatland. The focus of this study was on the dissolved CH₄ dynamics in a subarctic peatland ecosystem in Kobbefjord, West Greenland. A pore water sampling method was used to collect samples at four depths (5-, 15-, 25- and 35-cm depth) in the fen site. Stream water samples were collected from 13 plots around the study site. The results from the field sampling indicate that the average pore water concentration in early autumn (the onset of freezing) was generally higher than that in summer, in particular in the deep peat layer (around 30 cm beneath soil surface). According to the results of a correlation analysis, the average dissolved CH₄ magnitude was negatively correlated with air temperature (R = -0.961, p = 0.019) and surface CH₄flux (R= -0.880, P = 0.060). The higher concentration in early autumn suggests that the freezing ground and air temperature play an important role in the dissolved CH₄ dynamics. The frozen ground may restrict both CH₄emissions to the atmosphere and oxygen (O₂) diffusion into the peat, and temperature influences the CH₄ solubility in water. Meanwhile, a significant inverse correlation was found between the pore water concentration in the deep layer and the surface CH₄ flux, (R = -0.977, p = 0.012). Increased stream water CH₄ concentration near the fen site, corresponding with higher dissolved CH₄ concentration accumulated in the deep peat layer during the early autumn, further indicated that the freezing ground not only affected the CH₄ transport mechanisms, but also may have a physical effect on the dissolved CH₄ export. The results presented may bring contribute to a better understanding of the autumn CH₄ dynamics in northern peatlands.