Drivers of diffusive lake CH<sub>4</sub> emissions on daily to multi-year time scales

Abstract

<p><strong>Abstract.</strong> Lakes and reservoirs are important emitters of climate forcing trace gases. Various environmental drivers of the flux, such as temperature and wind speed, have been identified, but their relative importance remains poorly understood. Here we use an extensive field dataset to disentangle physical and biogeochemical controls on the turbulence-driven diffusive flux of methane (CH<sub>4</sub>) on daily to multi-year timescales. We compare 8 years of floating chamber fluxes from three small, shallow subarctic lakes (2010–2017, <i>n</i> = 1306) with fluxes computed using 9 years of surface water concentration measurements (2009–2017, <i>n</i> = 606) and a small-eddy surface renewal model informed by in situ meteorological observations. Chamber fluxes averaged 6.9 ± 0.3 mg m<sup>−2</sup> d<sup>−1</sup> and gas transfer velocities (<i>k</i><sub>600</sub>) from the chamber-calibrated surface renewal model averaged 4.0 ± 0.1 cm h<sup>−1</sup>. We find robust (<i>R</i><sup>2</sup> ≥ 0.93, <i>p</i> < 0.01) Arrhenius-type temperature functions of the CH<sub>4</sub> flux (<i>E</i><sub>a</sub>' = 0.90 ± 0.14 eV) and of the surface CH<sub>4</sub> concentration (<i>E</i><sub>a</sub>' = 0.88 ± 0.09 eV). Chamber derived gas transfer velocities tracked the power-law wind speed relation of the model (<i>k</i> ∝ <i>u</i><sup>3/4</sup>). While the flux increased with wind speed, during storm events (<i>U</i><sub>10</sub> ≥ 6.5 m s<sup>−1</sup>) emissions were reduced by rapid water column degassing. Spectral analysis revealed that on timescales shorter than a month emissions were driven by wind shear, but on longer timescales variations in water temperature governed the flux, suggesting emissions were strongly coupled to production. Our findings suggest that accurate short- and long term projections of lake CH<sub>4</sub> emissions can be based on distinct weather- and climate controlled drivers of the flux.</p>

Diel variability of methane emissions from lakes

“…As seen in other lake ecosystems, short-term variations in CH 4 flux can be driven by wind speed (26). This is in line with our data, which clearly showed that diel patterns of wind speed and CH 4 flux coincided with each other (SI Appendix, Fig.…”

Acoustic Mapping of Gas Stored in Sediments of Shallow Aquatic Systems Linked to Methane Production and Ebullition Patterns

“…In shallow waters, bubble mediated transport is the most efficient way of transferring methane to the atmosphere, bypassing methane oxidation in the oxic water column (McGinnis et al, 2006). Its temporal variability is a result of changes in local net methane production and accumulation in the sediment, and the episodic occurrence of triggers for bubble release (Varadharajan and Hemond 2012;Maecket al, 2014;Jansen et al, 2019). Whereas, spatial variability of ebullition in lakes and reservoirs results from variations of methane production rates in the sediment, which depend on sediment temperature (Wilkinson et al, 2015), sediment thickness (Maeck et al, 2013) and organic matter content (Grasset et al, 2018).…”

The IsoGenie database: an interdisciplinary data management solution for ecosystems biology and environmental research

“…Integrating data-and doing so across disciplines, beyond simple cataloging and indexing-becomes critically important as data analysis methods become increasingly sophisticated (Michener & Jones, 2012). As technological innovation allows, research is increasingly being performed across broader scales (e.g., from satellite data to processes at the micro and nanoscale) (Peters et al, 2008;Heffernan et al, 2014;Fei, Guo & Potter, 2016;Rose et al, 2017;Jansen et al, 2019a), and new and more diverse data are being generated. This has prompted international efforts to develop standards that make data more Findable, Accessible, Interoperable, and Reusable among different labs (FAIR principles) (Wilkinson et al, 2016;Brandizi et al, 2018).…”

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