Diel methane flux from a subtropical eutrophic pond in November based on continuous monitoring

Abstract

A field campaign was carried out to investigate continuous diel methane (CH4) flux from a subtropical eutrophic pond in November 2016. The diffusive methane flux of a single measurement had a range from 2.68 × 10−5 to 0.028 mmol·m−2·h−1 with an average of 0.011 ± 0.005 mmol·m−2·h−1. The diffusive methane flux of measurements from 9:00 to 10:30 and from 21:00 to 22:30 were very close to the average diffusive flux of all measurements. The bubble methane flux at different time measurements had much more variability than the diffusive methane flux. The bubble methane flux of a single measurement had a range from 0 to 0.312 mmol·m−2·h−1 with an average of 0.024 ± 0.054 mmol·m−2·h−1. For the eutrophic pond, the average bubble and diffusive CH4 flux were 0.56 ± 0.18 and 0.26 ± 0.04 mmol·m−2·day−1, respectively, and the CH4 ebullition flux accounted for 68.23% of the total flux. The maximum of the bubble CH4 flux was about 4.6 times of the minimum CH4 ebullition. The maximum of diffusive CH4 flux was ~ 1.7 times of the corresponding minimum. The diffusive methane fluxes in daytime and nighttime were almost equal. However, the bubble methane flux in daytime was 0.029 mmol·m−2·h−1, which was 1.6 times of that at night. Wind speed, the surface water temperature, and DO dominate methane effluxes from the pond, and the latter is in nature subjected to the metabolism of algae in the pond. However, key environmental factors which dominate gas flux processes vary with different weather conditions. Wind speed is unimportant when it is extremely low.