Temperature, Water Depth, and Flow Velocity Are Important Drivers of Methane Ebullition in a Temperate Lowland Stream

• Published in: Journal of geophysical research. Biogeosciences 2024-05, Vol.129 (5), p.n/a
• Main Authors: Bednařík, A., Bodmer, P., Darenova, E., Kokrda, L., Pavelka, M.
• Format: Article
• Language: English
• Subjects: Bubbles; Carbon dioxide; carbon dioxide emission; carbon fluxes; Creeks & streams; Diffusion; diffusive fluxes; Ecosystems; Emissions; Environmental factors; Estimates; Flow velocity; Fluxes; Grain size; Greenhouse gases; Heterogeneity; Methane; methane bubbles; methane production; methanotrophy; Rivers; Sediment; Sediment temperature; Sediments; Stream discharge; Stream flow; Streams; Variability; Velocity; Water depth
• ISSN: 2169-8953; 2169-8961
• DOI: 10.1029/2023JG007597

Streams and rivers are a well‐recognized source of methane (CH4), with high spatiotemporal variability in fluxes. However, CH4 release in form of bubbles (ebullition) is rarely included in current global CH4 emission estimates from lotic ecosystems, due to the lack of reliable models to upscale ebullition. Our study aimed to determine the importance of individual emission pathways (diffusion and ebullition) for total CH4 emissions from a lowland stream with low sediment heterogeneity and explore the relations of ebullition to environmental variables to build a stream ebullition model for this simplified system. We measured CH4 and carbon dioxide (CO2) diffusive emissions and ebullition from a temperate lowland stream in Czech Republic (Central Europe) during the ice‐free season 2021. The studied stream was a significant source of CH4 (mean 260 ± 107 mg CH4 m−2 day−1), with ebullition as a prevailing pathway of CH4 emission (mean 74 ± 7%, range 55%–85%) throughout the whole monitored period. CH4 ebullition showed a high spatiotemporal heterogeneity, with sediment temperature and water depth as the strongest predictors, followed by the interaction between flow velocity and sediment temperature. Our model explained 81% of total variance of CH4 ebullition and suggests that it is possible to model ebullitive fluxes in lowland streams with homogeneous sediments. Since CH4 was an important part of the total CO2‐equivalent emissions from the examined stream, accounting for mean (±SD) 35 ± 7.4%, and ebullition the majority of the CH4 emission, the ability to adequately model ebullition is pertinent for lowland streams. Plain Language Summary Streams and rivers are one of the natural sources of methane (CH4), an important greenhouse gas. CH4 can be released from water by two different emission pathways—by diffusion and by ebullition (in the form of bubbles). The magnitude of CH4 emissions from streams, especially the release of bubbles, considerably varies between streams or stream sections, and between seasons. Therefore, it is challenging to estimate and model the ebullitive CH4 emissions from streams with high reliability and include them properly in current global CH4 emission estimates from natural ecosystems. We studied the importance of individual CH4 emission pathways and their relations to environmental factors in a lowland stream with low variability in sediment characteristics, such as grain size, and carbon or nitrogen content. We found that CH4 bubble e