Biotic and Abiotic Control Over Diurnal CH4 Fluxes in a Temperate Transitional Poor Fen Ecosystem

Abstract

To understand the variability of methane (CH 4 ) fluxes between a temperate mid-altitude 15 Sphagnum-dominated peatland and the atmosphere, we monitored simultaneously eddy-covariance, 16 hydrometeorological and physical parameters between April 2019 and December 2021. The site was 17 a CH 4 source for the atmosphere, with a cumulative emission of 23.9 ± 0.6 g C m -2 year -1 . At the 18 interannual scale, deeper water table during vegetation growth periods resulted in lower CH 4 fluxes 19 (FCH4), and reciprocally. Furthermore, the seasonal temperature variation of the anaerobic peat layer 20 was a good predictor for FCH4. However, while the lowest temperatures occurred between December 21 and February, the lowest FCH4 were observed between March and May, with around 30 % of negative 22 FCH4. Indeed, the fastest increase in temperature of the aerobic layer likely stimulated methanotrophy 23 at the expense of methanogenesis. Negative FCH4, systematically observed at midday, were 24 concurrent with high photon flux densities, latent heat fluxes, and net negative ecosystem CO 2 25 exchanges, suggesting the control of photosynthesis over CH 4 oxidation. Moreover, our results 26 highlighted marked diurnal cycles with FCH4 maximal at night and minimal at midday for all seasons. 27 This diurnal cyclicity is in opposition to what is typically known for peatlands dominated by vascular 28 plants. Physical parameters, such as soil surface temperature and sensible heat fluxes, likely contribute 29 to this diurnal FCH4 cyclicity and require further investigation. Our study thus demonstrates that Page 1 of 42 Ecosystems 30 diurnal variations of FCH4 must be considered before upscaling to seasonal or annual cycles, along 31 with the effect of vegetation on CH 4 transfer and oxidation processes. 32

Origin and fate of dissolved inorganic carbon in a karst groundwater fed peatland using δ13CDIC

“…The important and systematically positive ∆δ 13 C DIC values of the deep catotelm layer could result from methane production, broadly observed in peatlands and resulting in an isotopic enrichment of δ 13 C DIC (Campeau et al, 2018;Corbett et al, 2013;Galand et al, 2010;Holmes et al, 2015;Lansdown et al, 1992;Steinmann et al, 2008). Such a process is in agreement with the methane fluxes observed at the Forbonnet peatland during the period of field sampling (Jacotot et al 2021;Lhosmot et al, 2022). Consistently, the highly positive ∆δ 13 C DIC values of the catotelmic bog samples exclude an atmospheric influence.…”

CO2 and CH4 fluxes from inundated floodplain ponds: role of diel variability and duration of inundation

“…In accordance with our results, higher nighttime CO 2 fluxes compared to daytime fluxes have been observed, for example, in rice paddies (Min and Rulík, 2020), in European and Arctic streams (Rocher-Ros et al, 2020;Attermeyer et al, 2021), and global rivers (Gómez-Gener et al, 2021). A recent study by Lhosmot et al (2022) also showed a diel variability of CH 4 fluxes, with higher fluxes at night and lower during the day. The ecosystem is different (peatland) but is close to rice paddies as cited here.…”

Mountain Peatlands and Drought: Carbon Cycling in the Pyrenees Amidst Global Climate Change

“…In particular, Lhosmot et al. (2022); Knox et al. (2021) showed that for temperate Sphagnum peatlands, diurnal methane fluxes reach their minimum when PAR and photosynthesis are at their maximum.…”

“…Recent publications on methane emissions from peatlands have highlighted the links observed between photosynthesis fluxes, PAR and methane fluxes to explain this observation. In particular, Lhosmot et al (2022); Knox et al (2021) showed that for temperate Sphagnum peatlands, diurnal methane fluxes reach their minimum when PAR and photosynthesis are at their maximum. In our model, The CI × AT product modulates the seasonality of CH 4 fluxes, the latter widely documented and linked to soil and air temperature (Chang, 2022;Chi et al, 2020).…”