A primary study of the methane flux on the water-air interface of eight lakes in winter, China

In order to examine the winter daily change of the methane flux of the eight lakes in China,the methane flux on the water-air interface was observed continuously for 24-hour based on a closed-chamber and gas chromatog- raphy-based system from 14,Dec.in 2004 to 14,Jan.in 2005,including Lake Dongting,Lake Poyang,Lake Chaohu,Lake Nansi,Lake Hongze,Lake Fuxian,Lake Erhai and Lake Dianchi.Furthermore,the total methane emission from lakes to atmosphere was calculated during the winter period according to the average methane flux of the eight lakes.The result suggested that Lake Poyang,Lake Chaohu,Lake Nansi,Lake Hongze and Lake Dianchi were the source of the atmospheric methane during the time,with the average flux of 0.818,0.021,0.034,0.019 and 0.163 mg/(m~2·h)respectively.As for Lake Dongting,Lake Fuxian,Lake Erhai they were yet the methane source to the atmosphere by the average flux of 24 h,which was 0.199,0.012 and 0.044 mg/(m~2·h)respective- ly,though they were the sink at some time.There was little difference among the methane flux of these eight lakes, and it was mainly affected by wind speed.In addition,no obvious statistic relationships were found between the flux and water temperature,and between the temperature in the sample bucket and the concentration of DOC.The average flux of eight lakes was 0.164±0.140 mg/(m~2·h).Multiplied by 9.1×10~4 km~2 which is the surface ar- ea of all lakes in China and 90-day for winter period,a total of 3.22±2.75×10~7 kg of methane was estimated to e- mit to the atmosphere from the winter lakes.Compared with other emission sources,the methane emission from lakes was lower,only 2.8‰of the total methane emission from rice field in 1990.