Methane Bubbling From Northern Lakes: Present and Future Contributions to the Global Methane Budget

Institute of Arctic Biology, University of Alaska, Fairbanks, AK 99775, USA.
Philosophical Transactions of The Royal Society A Mathematical Physical and Engineering Sciences (Impact Factor: 2.15). 08/2007; 365(1856):1657-76. DOI: 10.1098/rsta.2007.2036
Source: PubMed


Large uncertainties in the budget of atmospheric methane (CH4) limit the accuracy of climate change projections. Here we describe and quantify an important source of CH4 -- point-source ebullition (bubbling) from northern lakes -- that has not been incorporated in previous regional or global methane budgets. Employing a method recently introduced to measure ebullition more accurately by taking into account its spatial patchiness in lakes, we estimate point-source ebullition for 16 lakes in Alaska and Siberia that represent several common northern lake types: glacial, alluvial floodplain, peatland and thermokarst (thaw) lakes. Extrapolation of measured fluxes from these 16 sites to all lakes north of 45 degrees N using circumpolar databases of lake and permafrost distributions suggests that northern lakes are a globally significant source of atmospheric CH4, emitting approximately 24.2+/-10.5Tg CH4yr(-1). Thermokarst lakes have particularly high emissions because they release CH4 produced from organic matter previously sequestered in permafrost. A carbon mass balance calculation of CH4 release from thermokarst lakes on the Siberian yedoma ice complex suggests that these lakes alone would emit as much as approximately 49000Tg CH4 if this ice complex was to thaw completely. Using a space-for-time substitution based on the current lake distributions in permafrost-dominated and permafrost-free terrains, we estimate that lake emissions would be reduced by approximately 12% in a more probable transitional permafrost scenario and by approximately 53% in a 'permafrost-free' Northern Hemisphere. Long-term decline in CH4 ebullition from lakes due to lake area loss and permafrost thaw would occur only after the large release of CH4 associated thermokarst lake development in the zone of continuous permafrost.

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    • "These results provide additional evidence that in non-yedoma lakes, the lower organic carbon inputs fuels more weakly methanogenesis and aerobic processes including MO than in yedoma lakes, resulting in a lower seasonal variation of CH 4 and DO concentration. Another reason is that yedoma lakes have a significantly higher ebullition year round (Walter et al., 2007; Sepulveda-Jauregui et al., 2015). Even during winter , Greene et al. (2014) found that 80 % of CH 4 in ebullition bubbles trapped under the ice cover dissolves into the lake water column before being confined within the growing ice sheet, leading to elevated dissolved CH 4 beneath the ice. "
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    ABSTRACT: Methanotrophic bacteria play an important role oxidizing a significant fraction of methane (CH4) produced in lakes. Aerobic CH4 oxidation depends mainly on lake CH4 and oxygen (O2) concentrations, in such a manner that higher MO rates are usually found at the oxic/anoxic interface, where both molecules are present. MO also depends on temperature, and via methanogenesis, on organic carbon input to lakes, including from thawing permafrost in thermokarst (thaw)-affected lakes. Given the large variability in these environmental factors, CH4 oxidation is expected to be subject to large seasonal and geographic variations, which have been scarcely reported in the literature. In the present study, we measured CH4 oxidation rates in 30 Alaskan lakes along a north-south latitudinal transect during winter and summer with a new field laser spectroscopy method. Additionally, we measured dissolved CH4 and O2 concentrations. We found that in the winter, aerobic CH4 oxidation was mainly controlled by the dissolved O2 concentration, while in the summer it was controlled primarily by the CH4 concentration, which was scarce compared to dissolved O2. The permafrost environment of the lakes was identified as another key factor. Thermokarst (thaw) lakes formed in yedoma-type permafrost had significantly higher CH4 oxidation rates compared to other thermokarst and non-thermokarst lakes formed in non-yedoma permafrost environments. As thermokarst lakes formed in yedoma-type permafrost have been identified to receive large quantities of terrestrial organic carbon from thaw and subsidence of the surrounding landscape into the lake, confirming the strong coupling between terrestrial and aquatic habitats and its influence on CH4 cycling.
    Biogeosciences 08/2015; 12(15):4595-4606. DOI:10.5194/bg-12-4595-2015 · 3.98 Impact Factor
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    • "A possible explanation for the lack of detectable CH 4 production in the permafrost tunnel could be a paucity of viable methanogens naturally present in deep permafrost soils (Wagner et al., 2007; Steven et al., 2006; Gilichinsky et al., 2003; Rivkina et al., 1998). In previous anaerobic incubations of deep permafrost, little or no CH 4 production has been observed and there was either no observed CH 4 production (non-yedoma permafrost; Wagner et al., 2007), a significant delay before detectable CH 4 production occurred (yedoma permafrost; Knoblauch et al., 2013), or no CH 4 production until samples were inoculated with modern lake sediments (yedoma permafrost; Walter et al., 2007; S. Zimov, personal communication, 2002). Since we observed CH 4 production in the Transitional permafrost (thawing yedoma) beneath Vault Lake but no CH 4 production in the permafrost tunnel samples (yedoma and underlying gravel horizons) it is possible that, in thermokarst lake environments, CH 4 produced from yedoma OM requires the reproduction of modern and/or ancient microbes along a thermally expanding substrate source as permafrost thaws radially beneath lakes. "
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    ABSTRACT: Thermokarst (thaw) lakes emit methane (CH4) to the atmosphere formed from thawed permafrost organic matter (OM), but the relative magnitude of CH4 production in surface lake sediments vs. deeper thawed permafrost horizons is not well understood. We assessed anaerobic CH4 production potentials from various depths along a 590 cm long lake sediment core that captured the entire sediment package of the talik (thaw bulb) beneath the center of an interior Alaska thermokarst lake, Vault Lake, and the top 40 cm of thawing permafrost beneath the talik. We also studied the adjacent Vault Creek permafrost tunnel that extends through ice-rich yedoma permafrost soils surrounding the lake and into underlying gravel. Our results showed CH4 production potentials were highest in the organic-rich surface lake sediments, which were 151 cm thick (mean ± SD 5.95 ± 1.67 μg C-CH4 g dw−1 d−1; 125.9± 36.2 μg C-CH4 g C−1org d−1). High CH4 production potentials were also observed in recently-thawed permafrost (1.18± 0.61 μg C-CH4g dw−1 d−1; 59.60± 51.5 μg C-CH4 g C−1org d−1) at the bottom of the talik, but the narrow thicknesses (43 cm) of this horizon limited its overall contribution to total sediment column CH4 production in the core. Lower rates of CH4 production were observed in sediment horizons representing permafrost that has been thawed in the talik for longer periods of time. No CH4 production was observed in samples obtained from the permafrost tunnel, a non-lake environment. Our findings imply that CH4 production is highly variable in thermokarst-lake systems and that both modern OM supplied to surface sediments and ancient OM supplied to both surface and deep lake sediments by in situ thaw as well as shore erosion of yedoma permafrost are important to lake CH4 production.
    Biogeosciences 07/2015; 12:4317-4331. DOI:10.5194/bg-12-4317-2015 · 3.98 Impact Factor
    • "As shown by a study of DelSontro et al. (2010), ebullitive methane emissions per unit area from temperate hydropower reservoirs are comparable to those in tropical waters. A dominant pathway of methane emissions from shallow aquatic ecosystems is ebullition, which refers to the sudden release of methane bubbles from bottom sediments into the air (Casper et al. 2000; Walter et al. 2007). These bubbles are difficult to observe and to estimate well with conventional sampling methods (gas traps or optical devices) because their occurrence is episodic (Joyce and Jewell 2003) and " their presence is not representatively captured with usual shortterm measurements " (Bastviken et al. 2011). "
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    ABSTRACT: Methane represents an important greenhouse gas, and its ebullition is a significant way of releasing gas from bottom sediments of shallow fresh waters to the atmosphere. Estimation of ebullition is complicated because of high spatiotemporal variability; however, a hydroacoustical survey represents an effective method for quantifying it. Commonly used vertical beaming in deep waters can be quite limited in very shallow waters. This study was thus aimed to investigate the possibility of using a horizontally oriented sonar beam for gas bubble quantification. Artificially prepared methane bubbles of various sizes, ranging from 2.5 to 905 × 10−3 mL (1.7–12 mm of equivalent spherical diameter), were released from a depth of 6 m in a freshwater reservoir. The acoustic target strength (TS) of these bubbles was observed using both the vertical and horizontal beams of a 120 kHz frequency split-beam sonar. TS obtained in both the vertical and horizontal modes increase with growing bubble size. However, for identical bubble size, the vertical observation gives stronger TS than the horizontal one. Further, TS distribution around mean value is wider with an increase in bubble size, and this distribution is greater in case of the horizontal mode of observation than vertical. It was observed that during bubble rise TS changes for both the vertical and horizontal mode of observation lie within the range of standard deviation of TS measurement; hence, depth is not relevant for TS regression models used in depth up to 6 m.
    Limnology and oceanography, methods 06/2015; DOI:10.1002/lom3.10051 · 2.25 Impact Factor
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