Methane emission by bubbling from Gatun Lake, Panama

¹National Center for Atmospheric Research, Boulder, CO, USA

²U.S. Geological Survey, 3215 Marine Street, Boulder, CO 80303-1066, USA

Abstract

We studied methane emission by bubbling from Gatun Lake, Panama at water depths of less than 1 m to about 10 m. Gas bubbles were collected in floating traps deployed during 12- to 60-hour observation periods. Comparison of floating traps and floating chambers shoed that about 98% of emission occurred by bubbling and only 2% occurred by diffusion. Average methane concentration of bubbles at our sites varied from 67% to 77%. Methane emission by bubbling occurred episodically, with greatest rates primarily between the hours of 0800 and 1400 LT. Events appear to be triggered by wind. The flux of methane associated with bubbling was strongly anticorrelated with water depth. Seasonal changes in water depth caused seasonal variation of methane emission. Bubble methane fluxes through the lake surface into the atmosphere measured during 24-hour intervals were least (10-200 mg/m²/d) at deeper sites (>7 m) and greates (300-2000 mg/m²/d) at shallow sites (<2 m).

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