Spatial-temporal dynamics and influencing factors of CO2 and CH4 fluxes in a double-water-level regulated Hanfeng Lake in the Three Gorges Reservoir
This study investigated the fluxes and concentrations of CO2 and CH4 in Hanfeng Lake,using the floating chamber method and headspace equilibrium method,to reveal spatio-temporal dynamics and driving factors of CO2 and CH4 emissions under varing water level fluctuations.The results showed that Hanfeng Lake was a weak CO2 emission source,with a flux range of-64.34 to 128.37mmol/(m2·d)and an average of(35.8±45.2)mmol/(m2·d),which was much lower than that of other waters in the Three Gorges Reservoir.Meanwhile,Hanfeng Lake was a strong CH4 emission source.Although the CH4 flux showed strong variations with ranges of 0.43～36.93mmol/(m2d),its average value((3.87±5.08)mmol/(m2·d))was much higher than that of other regions in the Three Gorges Reservoir.The total emissions of CO2 and CH4 emitted to the atmosphere by Hanfeng Lake was 1415.48 and 133.54t,respectively,accounting for 26.86％of the total carbon storage of Hanfeng Lake,which indicated that Hanfeng Lake had an active carbon metabolism.From January to December,the CO2 emission flux in Hanfeng Lake showed a seasonal pattern of significant decrease and then rapid increase,and CH4 showed an almost opposite seasonal change.The seasonal dynamics were strongly disturbed by the double-water-level regulation.Higher CO2 and lower CH4 emission during the high water level period of the Three Gorges.During the Hanfeng water level period,CO2 emission was weaker,but CH4 emission was stronger.CO2 and CH4 emissions were stronger during the Three Gorges backwater period.Correlation analysis showed that CO2 emission flux was negatively correlated with Chl-a,algal density and pH.The change of primary production caused by algae blooms was the key factor to dominate the seasonal dynamics of CO2 emissions,and even led to the obvious CO2 source-sink transition in Hanfeng Lake.CH4 fluxes were positively correlated with TOC,DOC,TN,NO3--N and algal density,indicating that the seasonal dynamics of CH4 emission were dominated by nitrogen accumulation and algal metabolism.The CO2 emission flux in Hanfeng Lake showed a spatial characteristic of first decreasing and then increasing from upstream to downstream,which was opposite to the spatial dynamic of CH4 emission flux.This spatial characteristic was caused by the incoming rivers and water level fluctuation.In general,water level fluctuation obviously interfered with the correlation between water environment parameters and carbon emissions,resulting in different key indicators of CO2 and CH4 emission fluxes at different water levels.
Hanfeng Lakedouble-water-level regulationCO2 and CH4 fluxesspatial-temporal variationsinfluencing factors
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