Lake Sediments From Littoral and Profundal Zones are Heterogeneous but Equivalent Sources of Methane Produced by Distinct Methanogenic Communities—A Case Study From Lake Remoray

Abstract

Methane ranks just behind carbon dioxide as a major greenhouse gas, with a 12-year lifetime in the atmosphere, a global warming potential 72 times higher than CO 2 over a 20-year timescale (25 times higher over 100 years), and a radiative forcing of +0.48 W m −2 (IPCC, 2007). Methane concentration in the atmosphere is currently about 1,850 ppb (Nisbet et al., 2019), which is an increase of more than 150% since the pre-industrial era and rising fast at the unprecedented rate of >5 ppb yr −1 in the 2004-2017 period (Nisbet et al., 2019).Atmospheric methane is mostly anthropogenic: fossil fuel extraction and agricultural practices account for about 60% of methane emissions (Saunois et al., 2020). Other sources are natural: wetlands ecosystems are the biggest natural source of atmospheric methane, followed by lake ecosystems which account for 6%-16% of non-anthropogenic emissions (Bastviken et al., 2004). Depending on the methodologies applied, lakes are estimated to be responsible for up to 50 (Johnson et al., 2022) to 150 Tg (Saunois et al., 2020) of C-CH 4 emitted to the atmosphere per year. Recent models project that lake emissions will increase under the combined effects of

Spatio-temporal variations of methane fluxes in sediments of a deep stratified temperate lake

“…Profundal sediments differ spatially from littoral sediments in terms of light exposure, 39 quality and quantity of available OC, frequency of sediment resuspension, etc., which thus influence methanogenic and methanotrophic community structure and their activities depending on the lake thermal stratification dynamics. 40 , 41 , 42 Firstly, in addition to the much warmer epilimnion than hypolimnion during thermal stratification ( Figures 2 A–2C), a more sensitive thermal response of MP in littoral sediments ( Figures S5 C–S5E) was observed in Lake Stechlin; similar findings were also reported by Lofton et al. 43 in Arctic lakes.…”

“…Secondly, methanogenesis in the littoral and profundal zones could be driven by distinct differences in substrate availability that were regulated by quantity and source of sediment OC. 42 This in-lake spatial variability could be caused by distinct distribution patterns of degradable sediment OC. 11 For example, in Lake Stechlin, littoral sediments receive abundant fresh and labile substances, i.e., via fallen leaves 22 and submerged macrophytes, 21 and have a C:N value of 10.6–26, especially in the deep epilimnion.…”