Spatial and seasonal variability of diffusive methane emissions from the Three Gorges Reservoir

To investigate temporal and spatial variations in diffusive CH4 emission from the surface of the Three Gorges Reservoir, CH4 emissions were measured using the static chamber technique along the mainstream of the reservoir from January to December 2010. The overall average CH4 flux is 7.93 mg CH4 m−2 d−1, which is comparable to those from other temperate reservoirs but significantly lower than those from tropical reservoirs. Seasonal variations showed that CH4 emission reached the maximum in the summer and turned to the low levels in the other seasons; such variations reflected the seasonal dynamics of temperature, dissolved oxygen, and water velocity. Moreover, the yearly average CH4 flux decreased from upstream to downstream before the Three Gorges Dam, but CH4 emission from the surface of the downstream river was higher than that from the surface at Zigui, the upstream water before the Three Gorges Dam. The differences in water velocity and allochthonous input of organic matter probably caused the spatial variations in CH4 emission. These results indicate that systematic sampling is needed to better estimate CH4 emission through coverage of the temporal and spatial scales and to better assess the influence of CH4 emission from the Three Gorges Reservoir on climate change in China, as well as the rest of the world.

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