Diurnal variation in methane flux in a low-arctic fen in Southwest Greenland

Abstract: Popular science: A Day in the Life of a Methane Bog Methane gas is continuously released from wetlands around the world. In Kobbefjord, Greenland the release of methane is low during the cold of winter and higher in warm summer months. But the amount released also varies from day to night; a pattern that has to do with both temperature and light. Methane is a waste product from bacteria living in the soil below the groundwater table. The bacteria producing methane are only able to live where no oxygen is present. Their production of methane is affected by plants growing at the ground surface above them, as the plants release sugars and oxygen into the soil through their roots. The bacteria consume sugars from the plants which helps them to decompose organic matter in the soil. On the other hand, oxygen released into the soil by plants causes methane production to drop, as no methane is produced where oxygen is present. How much methane is released from the wetland into the atmosphere depends partly on the amount produced, but also on how it is transported to the surface. In the same way that plants are able to transport oxygen from the air into the soil, methane in the soil can pass to the atmosphere through the roots, stems and leaves of plants. This is a relatively fast mode of transport. Alternatively, methane can move up slowly through the soil, but near the ground surface there are bacteria which consume methane as it rises up from below; therefore part of it never makes it to the surface. Both the bacteria that produce and those that consume methane are more active at warm than at cold temperatures. The same is true for plants, but these are also more active in light than in darkness. As a result, the plants release more sugars into the soil and usually transport more oxygen and methane during the day when it is light and warm. The methane producing bacteria often live at a depth in the soil where there is only little temperature difference between day and night. But the methane consuming bacteria near the surface are more active by day than at night because of the higher temperature. The amount of methane released at the surface may vary from time to time and from place to place depending on factors such as light, temperature, groundwater table depth, plant species, soil type etc. At the study site in Kobbefjord, the amount of methane released was in some periods higher by day and in others higher at night. Analyses showed that temperature and light both had a role to play in this, but there was not enough information available to explain which mechanisms were responsible. Some of the factors mentioned above may well explain the change, but not all were measured at the time of the study. Most probably, plants are important for the short term variations in methane patterns.