Methane budget in eutrophic lake, Lake Tega

Abstract

The observation of methane was conducted in the water of Lake Tega in Japan, identified as a eutrophic lake to evaluate the influence to the atmospheric methane concentration. In the surface water, methane was highly oversaturated with respect to the atmospheric methane. The degree of methane saturation ranged between 400% and 87,000%. The methane diffusive flux from the lake surface to the atmosphere was calculated to be 12.7 mgC-CH₄/m²/day. A one box model was applied to the methane in the lake water to test the higher methane concentration. It revealed that, a larger amount of methane was supplied to the lake water from the lake sediment. Almost of all the methane supplied to the lake water was rapidly released to the atmosphere, with the mean residence time of about 1 day. Seasonally, a 20% of the methane supplied was biologically oxidized in the water column.