Abstract: The chamber method is widely used to measure CO₂ and CH₄ 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 CO₂ and CH₄ 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 CO₂ and CH₄ 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 CO₂ flux, when CO₂ was emitted from the pond, the opaque chamber overestimated the CO₂ flux by 90%; when CO₂ was absorbed by the pond, the opaque chamber underestimated the CO₂ flux by 50%. The CH₄ diffusion flux measured by the opaque chamber was 40% lower than that measured by the transparent chamber. There was no significant difference between CO₂ and CH₄ flux measured by the chamber with and without air pressure equalizing device. CO₂ flux observed by the chamber without fan had poor representativeness, being 20% higher than that observed by the chamber with fan. Moreover, CH₄ flux emitted through different pathways could not be distinguished using the chamber without fan. Therefore, when the chamber method was used to observe the CO₂ and CH₄ flux at the water-air interface, the chamber shall be transparent and be installed with fan.

Key words: chamber method, chamber characteristics, water-air interface, CO₂ flux, CH₄ flux