Estimation on annual water-air CO2 and CH4 fluxes in Pengxi River, Three Gorges Reservoir

Estimation on annual greenhouse gas fluxes in reservoirs is crucial for the assessment of reservoir greenhouse gas effects. A 1a research was conducted in Pengxi River backwater area, Three Gorges Reservoir to estimate annual water-air CO2 and CH4 fluxes. Taken the 24h continuous monitoring data in Gaoyang Lake as reference, 2 methods, i. e. underwater topographical method and environmental controlling factor method, were carried out to estimate the annual fluxes based on monthly field data. The field sampling results showed that mean value of the CO2 fluxes among the sampling spot was (3.05±0.46) mmol/(m2· h), while that of CH4 was (0.0501±0.0096) mmol/(m2·h). The annual estimation of CO2 and CH4 fluxes in the Pengxi River backwater area based on underwater topographical method was 40060.5 t and 540.9 t respectively. With the environmental controlling factor method, the annual estimation of CO2 and CH4 fluxes was 39073.0 t and 467.2 t respectively. Taken the annual estimation result from environmental controlling factor method as reference, the weighted average CO2 fluxes during the study was 43.26 mmol/(m2·d), while that of CH4 was 1.42 mmol/(m2·d). Generally, both of the CO2 and CH4 weight average fluxes were shown to be in the mid-range in the global data sets, although that of CO2 was showed in slightly higher bound.