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

Abstract

AbstractStreams 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.