CH4 flux measured by a portable chamber using an infrared analyzer was compared with the flux by static chamber measurement for CW at 13 different sites from May 2012 to May 2017 in the Living Water Garden (LWG) in Chengdu, Sichuan Province, China, over 4 timescales (daily, monthly, seasonal, and annual). During the measurement period, a total of 1443 data were collected. CH4 fluxes were measured using the portable chamber method and the results showed that the annual mean and median CH4 flux values in the LWG were 17.4 mg m-2 h-1 and 6.2 mg m-2 h-1, respectively, ranging from - 19.7 to 98.0 mg m-2 h-1. Cumulative CH4 emissions for LWG ranged from - 0.17 to 0.86 kg m-2 year-1. Global warming potential (GWP, 25.7 kg CO2eq m-2 year-1) was at a high level, which means that the LWG was a source of CH4 emissions. Significant temporal variations on the 4 timescales were observed. And the asymmetry of measurement uncertainty of CH4 flux increases with the timescale. Although the total mean CH4 flux measured by the portable chamber method was 42.1% lower than that of the static chamber method, the temporal variation trends of CH4 flux were similar. The uncertainty of CH4 flux measured in portable chamber was more symmetrical than that in static chamber. These results suggest that the portable chamber method has considerable value as a long-term measurement method for CH4 flux temporal variations.
Keywords: Constructed wetland; Global warming potential; Methane flux; Portable chamber; Static chamber.