Long‐Term Measurements of Methane Ebullition From Thaw Ponds

• Published in: Journal of geophysical research. Biogeosciences Vol. 124; no. 7; pp. 2208 - 2221
• Main Authors: Burke, S. A., Wik, M., Lang, A., Contosta, A. R., Palace, M., Crill, P. M., Varner, R. K.
• Format: Journal Article
• Language: English
• Published: Washington Blackwell Publishing Ltd 01-07-2019; American Geophysical Union
• Subjects: Air temperature; Arctic zone; Atmospheric pressure; BASIC BIOLOGICAL SCIENCES; Bubbles; Bubbling; Concentration gradient; Ecosystems; Efflux; Emissions; ENVIRONMENTAL SCIENCES; environmental sciences & ecology; Fluctuations; Fluxes; Frozen ground; geology; GEOSCIENCES; Greenhouse effect; Greenhouse gases; Hydrology; Ice environments; Lakes; Methane; Peatlands; Permafrost; Physical characteristics; Physical properties; Ponds; Soil; Summer; Variability; Arctic region
• ISSN: 2169-8953; 2169-8961; 2169-8961
• DOI: 10.1029/2018JG004786

Arctic regions are experiencing rapid warming, leading to permafrost thaw and formation of numerous water bodies. Although small ponds in particular are considered hot spots for methane (CH4) release, long‐term studies of CH4 efflux from these surfaces are rare. We have collected an extensive data set of CH4 ebullition (bubbling) measurements from eight small thaw ponds (<0.001 km2) with different physical and hydrological characteristics over four summer seasons, the longest set of observations from thaw ponds to date. The measured fluxes were highly variable with an average of 20.0 mg CH4 · m−2 · day−1 (median: 4.1 mg CH4 · m−2 · day−1, n = 2,063) which is higher than that of most nearby lakes. The ponds were categorized into four types based on clear and significant differences in bubble flux. We found that the amount of CH4 released as bubbles from ponds was very weakly correlated with environmental variables, like air temperature and atmospheric pressure, and was potentially more related to differences in physical characteristics of the ponds. Using our measured average daily bubble flux plus the available literature, we estimate circumpolar thaw ponds <0.001 km2 in size to emit between 0.2 and 1.0 Tg of CH4 through ebullition. Our findings exemplify the importance of high‐frequency measurements over long study periods in order to adequately capture the variability of these water bodies. Through the expansion of current spatial and temporal monitoring efforts, we can increase our ability to estimate CH4 emissions from permafrost pond ecosystems now and in the future.
Plain Language Summary
Long‐term studies of methane emissions from thaw ponds are rare but essential for our understanding of how these ecosystems are responding to Arctic warming. Our study incorporates over 2,000 measurements of methane gas, collected over four summer seasons from eight small ponds located within one single peatland in northern Sweden. These ponds formed when frozen soil thawed due to increasing air temperatures. Ponds like these are known to release methane, a strong greenhouse gas, through bubbling, diffusion along a concentration gradient, and transport through plant internal structure, though bubbling is the least understood. We also used photographs collected with a drone to estimate the area of each pond. We found the ponds to vary widely in methane emission over time as well as between ponds. We also found that meteorological variables like air temperature and atmospheric pressure explained little of the variability in bubble flux we measured. Our measurements represent the longest record of bubble measurements from climate sensitive ponds to date and help us to better understand the amount of methane released and what controls it. It is important to include these bodies of water in our understanding of how Arctic areas are changing with increasing air temperatures.
Key Points
High‐frequency ebullition measurements over multiple seasons are important in constraining the CH4 contribution from small thaw ponds
Small thaw ponds (<0.001 km2) are important regional sources of ebullitive CH4 at high latitudes
Meteorological variables were very weakly correlated with thaw pond ebullition potential