METHANE EMISSION BY BUBBLING FROM GATUN LAKE, PANAMA

We studied methane emission by bubbling from Gatun Lake, Panama, at wa ter 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 showed that about 9 8% of methane emission occurred by bubbling and only 2% occurred by di ffusion. Average methane concentration of bubbles at our sites varied from 67% to 77%. Methane emission by bubbling occurred episodically, w ith greatest rates primarily between the hours of 0800 and 1400 LT. Ev ents appear to be triggered by wind. The flux of methane associated wi th bubbling was strongly anticorrelated with water depth. Seasonal cha nges in water depth caused seasonal variation of methane emission. Bub ble methane fluxes through the lake surface into the atmosphere measur ed during 24-hour intervals were least (10-200 mg m-2 d-1) at deeper s ites (>7 m) and greatest (300-2000 mg m-2 d-1) at shallow sites (<2 m) .