Abstract 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 (CH 4 ) release, long‐term studies of CH 4 efflux from these surfaces are rare. We have collected an extensive data set of CH 4 ebullition (bubbling) measurements from eight small thaw ponds (<0.001 km 2 ) 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 CH 4 · m −2 · day −1 (median: 4.1 mg CH 4 · 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 CH 4 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 km 2 in size to emit between 0.2 and 1.0 Tg of CH 4 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 CH 4 emissions from permafrost pond ecosystems now and in the future.
This dataset contains potential methane (CH4) production and oxidation rates and porewater chemistry (dissolved oxygen, pH, redox potential, dissolved CH4, and CH4 stable isotopes) measurements collected from hummocks and lawns in a poor fen in New Hampshire, USA. Potential CH4 production and oxidation rates determined via incubations and dissolved oxygen measurements were collected in July 2018. Porewater CH4 concentration, δ13C-CH4 and δD-CH3D, and Eh/pH were collected in July/August 2020. The data file contains a "README" tab with a guide for variable units and descriptions.
A dynamic dilution system for producing low mixing ratios of methyl bromide (MeBr) and a sensitive analytical technique were used to study the uptake of MeBr by various soils. MeBr was removed within minutes from vials incubated with soils and ~10 parts per billion by volume of MeBr. Killed controls did not consume MeBr, and a mixture of the broad-spectrum antibiotics chloramphenicol and tetracycline inhibited MeBr uptake by 98%, indicating that all of the uptake of MeBr was biological and by bacteria. Temperature optima for MeBr uptake suggested a biological sink, yet soil moisture and temperature optima varied for different soils, implying that MeBr consumption activity by soil bacteria is diverse. The eucaryotic antibiotic cycloheximide had no effect on MeBr uptake, indicating that soil fungi were not involved in MeBr removal. MeBr consumption did not occur anaerobically. A dynamic flowthrough vial system was used to incubate soils at MeBr mixing ratios as low as those found in the remote atmosphere (5 to 15 parts per trillion by volume [pptv]). Soils consumed MeBr at all mixing ratios tested. Temperate forest and grassy lawn soils consumed MeBr most rapidly (rate constant [k] = 0.5 min-1), yet sandy temperate, boreal, and tropical forest soils also readily consumed MeBr. Amendments of CH4 up to 5% had no effect on MeBr uptake even at CH4:MeBr ratios of 10(7), and depth profiles of MeBr and CH4 consumption exhibited very different vertical rate optima, suggesting that methanotrophic bacteria, like those presently in culture, do not utilize MeBr when it is at atmospheric mixing ratios. Data acquired with gas flux chambers in the field demonstrated the very rapid in situ consumption of MeBr by soils. Uptake of MeBr at mixing ratios found in the remote atmosphere occurs via aerobic bacterial activity, displays first-order kinetics at mixing ratios from 5 pptv to ~1 part per million per volume, and is rapid enough to account for 25% of the global annual loss of atmospheric MeBr.
Permafrost soils store over half of global soil carbon (C), and northern frozen peatlands store about 10% of global permafrost C. With thaw, inundation of high latitude lowland peatlands typically increases the surface-atmosphere flux of methane (CH4), a potent greenhouse gas. To examine the effects of lowland permafrost thaw over millennial timescales, we measured carbon dioxide (CO2) and CH4 exchange along sites that constitute a ∼1000 yr thaw chronosequence of thermokarst collapse bogs and adjacent fen locations at Innoko Flats Wildlife Refuge in western Alaska. Peak CH4 exchange in July (123 ± 71 mg CH4–C m−2 d−1) was observed in features that have been thawed for 30 to 70 (<100) yr, where soils were warmer than at more recently thawed sites (14 to 21 yr; emitting 1.37 ± 0.67 mg CH4–C m−2 d−1 in July) and had shallower water tables than at older sites (200 to 1400 yr; emitting 6.55 ± 2.23 mg CH4–C m−2 d−1 in July). Carbon lost via CH4 efflux during the growing season at these intermediate age sites was 8% of uptake by net ecosystem exchange. Our results provide evidence that CH4 emissions following lowland permafrost thaw are enhanced over decadal time scales, but limited over millennia. Over larger spatial scales, adjacent fen systems may contribute sustained CH4 emission, CO2 uptake, and DOC export. We argue that over timescales of decades to centuries, thaw features in high-latitude lowland peatlands, particularly those developed on poorly drained mineral substrates, are a key locus of elevated CH4 emission to the atmosphere that must be considered for a complete understanding of high latitude CH4 dynamics.
