In freshwater lakes, ebullition is an important pathway for biogenic methane (CH4) to escape from sediment and reach the atmosphere. However, the high spatial and temporal variability of ebullition limits our ability to accurately measure or predict CH4 fluxes from lakes. To explore factors controlling the spatial distribution of ebullition, we investigated free gas accumulation in bottom sediment of Lake Kinneret, Israel. Sediment cores were collected from four sites at different water depth and distance from the shore. Sediment porewater was analyzed for dissolved CH4 concentration, pH, DOC, acetate, and sulfate. Anaerobic CH4 production rates in sediment were determined by incubating sediment samples. For characterizing in situ sediment volumetric gas content, hydroacoustic measurements at various frequencies were conducted at the coring sites and along multiple transects across the lake. A minimum in CH4 production was observed in the upper 30 cm of sediment, which coincided with enriched porewater sulfate. The depth-integrated sediment CH4 production provides a robust estimate for long-term ebullition of CH4 from sediment, while short-term variability was associated with seasonal lake level change. Acoustic measurements revealed the absence of free gas in sediments of the littoral zone and low ebullition rates in the shallow water zones. For the first time, this study reports the role of CH4 production in determining the spatial variability of free gas content in freshwater sediments. The results further demonstrate the importance of sediment gas content in explaining spatial variability of gas ebullition in lakes.
Bibliographical noteFunding Information:
This study was financially supported by the German Research Foundation (grant LO 1150/5) and the Ministry of National Infrastructures, Energy and Water Resources, Israel (grant 214-17-007). Travel for S. Hilgert and K. Sotiri was supported by the GIZ GmbH and the German Academic Exchange Service (DAAD) within the project SeWaMa (Project ID: 57203877).
The authors would like to acknowledge Timo Fahlenbock, Semion Kaganovsky, Oz Zabari-Dar, Moti Diamant, and Beny Sulimani for their support in the field; Mr. Shimon Mendel from the Baruch Padeh Medical Center in Poriya for CT scans of the frozen sediment cores. We thank Captain Menachem Lev and his crew for their assistance onboard. Thanks to Daniel McGinnis for providing access to the instrument for stable isotope measurements and Wang Si for her help with the sediment incubation in laboratory. We also thank Werner Eckert for his critical comments to an earlier draft of the manuscript. We appreciate the helpful inputs from the anonymous referees and guest editor Gerald Dickens.
© 2019, Springer-Verlag GmbH Germany, part of Springer Nature.
ASJC Scopus subject areas
- Environmental Science (miscellaneous)
- Geotechnical Engineering and Engineering Geology
- Earth and Planetary Sciences (miscellaneous)