Diel variability of methane emissions from lakes

Abstract

Lakes are considered the second largest natural source of atmospheric methane (CH4). However, current estimates are still uncertain and do not account for diel variability of CH4 emissions. In this study, we performed high-resolution measurements of CH4 flux from several lakes, using an automated and sensor-based flux measurement approach (in total 4,580 measurements), and demonstrated a clear and consistent diel lake CH4 flux pattern during stratification and mixing periods. The maximum of CH4 flux were always noted between 10:00 and 16:00, whereas lower CH4 fluxes typically occurred during the nighttime (00:00–04:00). Regardless of the lake, CH4 emissions were on an average 2.4 higher during the day compared to the nighttime. Fluxes were higher during daytime on nearly 80% of the days. Accordingly, estimates and extrapolations based on daytime measurements only most likely result in overestimated fluxes, and consideration of diel variability is critical to properly assess the total lake CH4 flux, representing a key component of the global CH4 budget. Hence, based on a combination of our data and additional literature information considering diel variability across latitudes, we discuss ways to derive a diel variability correction factor for previous measurements made during daytime only.

Methane in the Danube Delta: the importance of spatial patterns and diel cycles for atmospheric emission estimates

“…Lakes showed concentrations similar to those of Pavel et al (2009) (see Table A1), although taken roughly 10 years later. The comparison to this earlier study indicates carbon turnover had not significantly changed during this period (Tudor et al, 2016;Spiridon et al, 2018). These concentrations ranged from the lowest 0.113 µmol L −1 to the highest 11.3 µmol L −1 both in May (largest concentration close to a channel).…”

“…Since the 1970s, the Danube Delta has been subject to eutrophication, with its peak during 1987-1988 (Cristofor et al, 1993;Galatchi and Tudor, 2006;Enache et al, 2019). After a decrease in nutrient loads in the 1990s, due to socioeconomic changes in eastern Europe, a slow decline of nutrient levels was observed (Rîşnoveanu et al, 2004;Pavel et al, 2009); however, more recent levels comparable to those in 1988 were reported (Tudor et al, 2016;Spiridon et al, 2018).…”

“…4a red box). The Danube Delta is known to have high levels of nutrients (Panin, 2003;Durisch-Kaiser et al, 2008;Spiridon et al, 2018) arriving from the Danube River. This could account for CH 4 higher concentrations, as well as saturation due to enhanced plankton growth being a source of additional labile organic matter fuelling CH 4 productivity in the sediments, which then outfluxes (Mendonça et al, 2012;Ward et al, 2017).…”

Unaccounted CO 2 leaks downstream of a large tropical hydroelectric reservoir

“…The availability of automated sensors capable of high-frequency measurements and long-term deployments make such an ideal framework realizable. The present study focused on CO 2 , but methane (CH 4 ) is an even more potent greenhouse gas (35) which also accumulates in the hypolimnia of lakes and then can be emitted to the atmosphere (8,36,37), and its emission from the reservoir surface can vary daily (38). Future research into the carbon cycling of dams and the emission hotspots downstream should therefore also assess methane fluxes in the downstream river system and their seasonal and subdaily variation.…”

Hotspots of Diffusive CO2 and CH4 Emission From Tropical Reservoirs Shift Through Time

“…10.1029/2020JG006014 8 of 19 followed by averaging the two annual estimates into an annual average estimate for each gas. Given that our calculations of total diffusive C emission are only based on daytime measurements (between 9 and 18 h), our results may be biased since they do not include any potential diel variations in diffusive C emissions and any specific mixing dynamics happening in the water column during the entire period of each hydrological season represented here (Podgrajsek et al, 2014;Rõõm et al, 2014;Sieczko et al, 2020).…”