Measurement of Methane Oxidation in Lakes:  A Comparison of Methods

Abstract

Methane oxidation in lakes constrains the methane emissions to the atmosphere and simultaneously enables the transfer of methane carbon to pelagic food webs. Several different methods have been used to estimate methane oxidation, but these methods have not previously been compared. In this study, we present methane oxidation estimates from three different lakes during summer and winter, using methods based on the transformation of added 14CH4, the fractionation of natural methane 13C, and the mass balance modeling of concentration gradients. All methods yielded similar results, including similar differences between lakes and seasons. Average methane oxidation rates varied from 0.25 to 81 mg of C m(-2) d(-1) and indicatethatthethree methods are comparable, although they to some extent take different processes into account. Critical issues as well as drawbacks and advantages with the used methods are thoroughly discussed. We conclude that methods using the stable isotope or mass balance modeling approach represent promising alternatives, particularly for studies focusing on ecosystem-scale carbon metabolism.

Emission and oxidation of methane in a meromictic, eutrophic and temperate lake (Dendre, Belgium)

“…Coleman et al (1981) showed that a was dependent on temperature. Bastviken et al (2002) determined a a of 1.0196 ± 0.002 for three Swedish lakes, whose temperature profiles are closer to what we observed. Based on this approach, we computed that in the Dendre Lake in summer, a large fraction (70e73%) of the upward flux of CH 4 was oxidized in a narrow depth interval (between 8.5 and 12 m; anoxic waters).…”

“…The total CH 4 emission to the atmosphere has been estimated to 540 Tg CH 4 yr À1 , with a significant contribution from inland waters (Bastviken et al, 2011;Borges et al, 2015;Holgerson and Raymond, 2016). The actual amount of CH 4 produced is higher, as a significant fraction of CH 4 produced is biologically oxidized before reaching the atmosphere (Bastviken et al, 2002). CH 4 oxidation limits the flux of CH 4 to the atmosphere, and in inland waters can fuel a microbial based food-web (Jones and Grey, 2011).…”

Oxic water column methanogenesis as a major component of aquatic CH4 fluxes

“…This approach was deemed more accurate in quantifying the slope at time 0, as traditional methods, such as log transformations followed by visual selection of the linear portion of the data set 31 , can introduce large errors in the slope of the regression line when deciding which points to fit and which to exclude. Although MOX was estimated only once, our estimates are within the range of pelagic MOX (0.170-0.250 mmol m À 3 per day) previously reported 31,32,62 , particularly for boreal lakes of similar trophic condition 62 .…”

“…Literature-derived values of a were used for both loss pathways. For evasion, an a value of 0.9992 was used 66 , and for MOX, the range reported by Bastviken et al 62 (0.9816-0.9792) was used.…”

“…For this analysis, we chose two very conservative, extreme (for oxic pelagic freshwaters) values in MOX rates (0 and 0.05 mmol m À 3 h À 1 ) and paired each rate with both minimum and maximum values reported for isotopic fractionation during MOX 62 (18.4 and 20.8%). Because the MOX rate of zero did not have associated isotopic fractionation, we calculated three different combinations of extreme parameters: no oxidation with no fractionation, high oxidation with low fractionation and high oxidation rates with high associated fractionation.…”