Methane bubbles in Lake Kinneret: Quantification and temporal and spatial heterogeneity

Abstract

The amount of methane bubbles rising from the bottom of Lake Kinneret was quantified by using a dual-beam echo sounder. Both echo-counting (EC) and echo integration (EI) techniques were implemented. Bubbles can confound the identification of fish targets because their acoustic sizes strongly overlap. Analysis of vertical changes in densities in the anoxic hypolimnion (with no fish) indicated that multiple targets were most abundant near the bottom, which caused an essential bias of bubble density estimates by EC. EI was a reliable tool for assessment of bubble density near the bottom. In the upper part of the water column, both techniques provided similar estimates of density of targets (mainly bubbles) because they were measured between dense fish schools during the daytime. The mean acoustic size of rising bubbles decreased in the hypolimnion but increased in the epilimnion, suggesting change in the relative importance of factors controlling gas volume. In summer and fall 2001, the bubbles became predominant echo-reflecting objects in the epilimnion. Temporal and spatial changes in bubble densities were highly heterogeneous, suggesting strong variability in factors affecting the gas ebullition. This variability should be taken into consideration when attempting to quantify the methane ebullition and assessing fish abundance in aquatic systems.

Response of the methanogenic microbial community of a profundal lake sediment (Lake Kinneret, Israel) to algal deposition

“…The highest input of organic matter into the profundal sediment occurs during the decline of this bloom between May and July (Pollingher 1986). Subsequently (July-November), high CH 4 emission from the profundal sediment is observed (Ostrovsky 2003). The increase in CH 4 bubbling intensity is probably triggered by the settling of organic matter onto the sediment (Eckert and Conrad 2007), similarly as observed in Lake Constance (Schulz and Conrad 1995).…”

Morphological record of oxygenic photosynthesis in conical stromatolites

“…S1), where they do not disrupt the surrounding laminae. The degradation of organic matter by methanogenic microbes can produce bubbles at large depths (16) that, coupled with methanotrophy, can lead to the precipitation of large-scale carbonate structures with central vents. These carbonate structures differ from conical stromatolites because Multiple pores surrounded by cyanobacterial filaments were present in the series of successive thick sections, confirming that the porosity was not an artifact.…”

A low‐cost automated trap to measure bubbling gas fluxes

“…Ebullition is a difficult process to quantify, because it is highly variable at several temporal and spatial scales (FechnerLevy and Hemond 1996;Ostrovsky 2003;Leifer et al 2004;Walter et al 2006). Considerable amounts of gas are often emitted during occasional, short-lived bubbling episodes.…”