[Effects of chamber characteristics on CO 2 and CH 4 flux at the water-air interface measured by the chamber method].

The chamber method is widely used to measure CO and CH flux in inland water. However, the designs of chamber used in various studies are different and lack unified standards, which would affect the observation results. To clarify the impacts of chamber characteristics, including light transmittance, air pressure difference inside and outside the chamber, and gas mixing degree in the chamber, on CO and CH flux measurements at the water-air interface, we compared the effects of transparent/opaque chamber, the chamber with/without air pressure equalizing device and fan on CO and CH flux measurements in the aquaculture pond, based on the multi-channel closed dynamic chamber system. The results showed that, during the daytime in summer, compared with the transparent chamber which could measure the actual CO flux, when CO was emitted from the pond, the opaque chamber overestimated the CO flux by 90%; when CO was absorbed by the pond, the opaque chamber underestimated the CO flux by 50%. The CH diffusion flux measured by the opaque chamber was 40% lower than that measured by the transparent chamber. There was no significant difference between CO and CH flux measured by the chamber with and without air pressure equalizing device. CO flux observed by the chamber without fan had poor representativeness, being 20% higher than that observed by the chamber with fan. Moreover, CH flux emitted through different pathways could not be distinguished using the chamber without fan. Therefore, when the chamber method was used to observe the CO and CH flux at the water-air interface, the chamber shall be transparent and be installed with fan.