Three Gorges Dam Operations Affect the Carbon Dioxide Budget of a Large Downstream Connected Lake

The effects of dams on carbon dioxide (CO2) fluxes in downstream lakes remain elusive. Here we combined eddy covariance observations and random forest models to examine multi-decadal variations in CO2 fluxes in the Poyang Lake, the largest freshwater lake in China, and quantified the contribution of the Three Gorges Dam (TGD), the world's largest hydraulic project. We found the lake fluctuated between CO2 source and sink in 1961-2016, and tended to be CO2 sink in the post-TGD period (2003-2016) when vegetation expanded early and spatially due to declining water level. TGD can explain approximately 6% of the total differences in annual CO2 fluxes, with major contributions in the impoundment period (up to 22% in middle September to October). The results show a positive side of operational major hydraulic projects on lake carbon sink, and probably caution the negative side of carbon release after dam removal.

Automated summary

This study examines the impact of the Three Gorges Dam on CO2 fluxes in China's largest freshwater lake, the Poyang Lake. The results show that the lake has transitioned from a CO2 source to a sink after the construction of the dam, especially during the impoundment period. The Three Gorges Dam explains approximately 6% of the annual differences in CO2 fluxes.