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

A field campaign was carried out to investigate continuous diel methane(CH_4) flux from a subtropical eutrophic pond in November 2016. The diffusive methane flux of a single measurement had a range from2.68 9 10-5 to 0.028 mmol·m^(-2)·h^(-1) with an average of0.011 ± 0.005 mmol·m^(-2)·h^(-1). The diffusive methane flux of measurements from 9:00 to 10:30 and from 21:00 to22:30 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 CH_4 flux were 0.56 ± 0.18 and 0.26 ± 0.04 mmol·m^(-2)·day^(-1),respectively, and the CH_4 ebullition flux accounted for68.23% of the total flux. The maximum of the bubble CH_4 flux was about 4.6 times of the minimum CH_4 ebullition.The maximum of diffusive CH_4 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, thesurface 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.

Applying a new method for direct collection, volume quantification and determination of N_2 emission from water

The emission of N2 is important to remove excess N from lakes, ponds, and wetlands. To investigate the gas emission from water, Gao et al.（2013） developed a new method using a bubble trap device to collect gas samples from waters. However, the determination accuracy of sampling volume and gas component concentration was still debatable. In this study, the method was optimized for in situ sampling, accurate volume measurement and direct injection to a gas chromatograph for the analysis of N2 and other gases. By the optimized new method, the recovery rate for N2 was 100.28% on average; the mean coefficient of determination（R2） was 0.9997; the limit of detection was 0.02%. We further assessed the effects of the new method, bottle full of water, vs. vacuum bag and vacuum vial methods, on variations of N2 concentration as influenced by sample storage times of 1,2, 3, 5, and 7 days at constant temperature of 15°C, using indices of averaged relative peak area（%） in comparison with the averaged relative peak area of each method at 0 day.The indices of the bottle full of water method were the lowest（99.5%–108.5%） compared to the indices of vacuum bag and vacuum vial methods（119%–217%）. Meanwhile, the gas chromatograph determination of other gas components（O2, CH4, and N2O） was also accurate. The new method was an alternative way to investigate N2 released from various kinds of aquatic ecosystems.