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Five shallow ponds of Yichang were selected to illustrate the characteristics of methane(CH 4 ) in subtropical eutrophic shallow ponds. CH 4 flux across the water-air interface was quantified with static floating chamber method for one year. Annual CH 4 fluxes of the five ponds were 4.495, 12.702, 6.827, 8.920, 17.560 mg·(m 2 ·h) -1 respectively. Diffusive CH 4 fluxes were 0.075, 0.087, 0.118, 0.086, 0.151 mg·(m 2 ·h) -1 respectively and bubble emissions were 4.420, 12.616, 6.709, 8.834, 17.409 mg·(m 2 ·h) -1 respectively. Over 98% of total CH 4 flux was bubble emission and CH 4 flux was apparently higher than other aquatic ecosystems. So the CH 4 flux of shallow waters was high and bubble emission was the dominant way. CH 4 emission would be largely underestimated if the research only focus on the diffusion discharge and ignore the bubble emission.

Thin boundary theory equation (TBL) is widely used to determine gas fluxes across water-air interfaces, and the gas transfer velocity ( k 600 ) is the key environmental factor in the equation. A monthly field campaign was carried out during one year to measure CH 4 flux and to probe its exchange rate across the air-water interface in a drinking reservoir and 5 adjacent ponds. The ranges of wind speed and surface water temperature were 0-0.75 m·s -1 and 6.3-30.9℃respectively, and their average values were 0.19 m·s -1 and 19.3℃ respectively. The gas transfer velocity of CH 4 varied from 0.20 to 1.99 cm·h -1 with an average of 0.50 cm·h -1 . Correlation functions between the gas transfer velocity and the wind speed at 10 m height ( U 10 ) and surface water temperature ( T w ) were given here to quantify k 600 . There were significant correlations between the fitted values and actual values both for original and bin-averaged data.

The Concentrations of dissolved CH 4 and CO 2 in Xiangxi Bay of the Three Gorges Reservoir from autumn to winter in 2014 were determined with headspace gas chromatography technology. Then their partial pressures of CH 4 and CO 2 were calculated according to the Henry's law. Their temporal variation and the effects of environmental parameters were also discussed. The results indicated that the CH 4 partial pressure in the surface water ranged 0.64-4.43Pa, with an average of (1.69±0.94)Pa. The CO 2 partial pressure varied from 49.90 to 868.91Pa, with the average of (328.48±251.63)Pa. The p CO 2 and p CH 4 had a strong negative correlation ( r =-0.618, P <0.01). During the period of monitoring, the p CO 2 and p CH 4 in surface water were significantly correlated with pH, DO, chlorophyll a, TP, surface water temperature and water level. Compared with p CH 4 , p CO 2 was more closely correlated with various environmental factors.