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Looking for gas bubbles in the sediment of lake Kinneret, Israel

The KIT team (Dr. Stephan Hilgert and Klajdi Sotiri) (Institute of Water and River Basins Management, Department of Aquatic Environmental Engineering, ISWW) joined an international research group with partners from the University Koblenz-Landau (Prof. Andreas Lorke), the TH Köln (Yannick Rathke and Timo Fahlenbock) as well as partners from Kinneret Limnological Laboratory, KLL (Dr. Ilia Ostrowsky) and University of Haifa (Regina Katsman).

Since Lake Kinneret is a well investigated research area it was chosen as location for the joint research campaign. It is the largest freshwater resource in Israel. It is located in the northern area of Israel, only 10 km distance from the Syrian border. It has an area of 166.7 km2 and it is the freshwater lake with the lowest altitude in the world (215 m – 209 m below sea level). The maximum depth of Lake Kinneret reaches 43 m. It main water inflow is the Jordan River. Further water inflows come from underground springs, which contribute to the water balance of the lake.

Methane emissions from water bodies are still in the focus of aquatic research. Especially man-made water bodies (reservoirs, impounded rivers) are known to contribute to methane fluxes to the atmosphere and therefore possibly to climate change. However, conditions of methane production, storage in the sediment and spatial variability are still not entirely understood.

Focusing on a better understanding of the conditions of gas bubble production, localization of the bubbles within the sediment volume and the distribution over the area of the lake, diverse measurements were conducted. Echosounding measurements were accomplished by ISWW and KLL. Three different hydroacoustic systems were used. One single beam echosounder with a high and low frequency, a parametric sub-bottom profiler and a split beam echo sounder for bubble detection. Static measurements as well as transect measurements covering the entire lake were conducted. These measurements aim on the hydroacoustic detection of bubbles in the sediment and in water column. They we accompanied by ground truthing measurements. A newly developed freeze corer by the TH Köln was used to produce least disturbed sediment cores, still containing the bubbles in the sediment matrix. The cores were CT scanned in a local hospital, in order to obtain gas void 3D information. In parallel, regular sediment cores were taken for incubation experiments for potential methane production measurements (Uni Landau). For long-term measurements of gas fluxes, automated bubble traps were installed at the sampling stations.

The obtained data and results will be processed in the coming month and will contribute to a better understanding of processes leading to methane emissions from water bodies. The hydro acoustic data may help understanding the distribution pattern of production hot-spots in water bodies.