Title:

Long-Term Measurements of Methane Ebullition From Thaw Ponds

Arctic regions are experiencing more rapid warming that other parts of the world, leading to destabilization of carbon (C) that has been locked up in permafrost, especially in peatlands where the C content of the peat is very high. This destabilization due to thaw is leading to the development of small thaw ponds that are known to be sources of methane (CH4) to the atmosphere, yet there is a lack in long-term studies of CH4 emission from these formations. At a site in northern Sweden, we have collected over 2000 measurements of CH4 ebullition, or bubbling, from eight small thaw ponds (<0.001 km2) differing in physical and hydrological characteristics over four growing seasons (2012-2015), making this study the largest dataset of thaw pond measurements of CH4 to date. We found ebullitive emission to be highly variable in space and time, with an average emission rate of 20 mg CH4 m-2 d-1. Ebullitive emission was weakly correlated with environmental conditions like atmospheric pressure and temperature and potentially more influenced by the physical characteristics of the ponds themselves. Based on our findings and the available literature, we estimate that small ponds (< 0.001 km2) emit between 0.2 and 1.0 Tg of CH4 through ebullition. Our study exemplifies the importance of long-term studies to adequately capture the rate of CH4 ebullition from these highly dynamic formations. With an increase in the number of long-term studies such as this, we will be better able to model CH4 emissions from peatland ecosystems in the future.

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