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Magnitudes and Drivers of Greenhouse Gas Fluxes in Floodplain Ponds During Drawdown and Inundation by the Three Gorges Reservoir
Author(s) -
Miller B. L.,
Chen H.,
He Y.,
Yuan X.,
Holtgrieve G. W.
Publication year - 2019
Publication title -
journal of geophysical research: biogeosciences
Language(s) - English
Resource type - Journals
eISSN - 2169-8961
pISSN - 2169-8953
DOI - 10.1029/2018jg004701
Subject(s) - floodplain , diel vertical migration , environmental science , drawdown (hydrology) , hydrology (agriculture) , greenhouse gas , ecosystem , water level , hydropower , groundwater , atmospheric sciences , ecology , aquifer , geology , oceanography , geotechnical engineering , cartography , geography , biology
Hydropower reservoirs are well‐known emitters of greenhouse gases to the atmosphere. This is due in part to seasonal water level fluctuations that transfer terrestrial C and N from floodplains to reservoirs. Partial pressures and fluxes of the greenhouse gases CH 4 , CO 2 , and N 2 O are also a function of in situ biological C and N cycling and overall ecosystem metabolism, which varies on a diel basis within inland waters. Thus, greenhouse gas emissions in hydropower reservoirs likely vary over seasonal and diel time scales with local hydrology and ecosystem metabolism. China's Three Gorges Reservoir is among the largest and newest in the world, with a floodplain that encompasses approximately one third of the reservoir area. We measured diel partial pressures and fluxes of greenhouse gases in ponds on the Three Gorges Floodplain. We repeated these measurements on the submerged floodplain following inundation by the Three Gorges Reservoir. During reservoir drawdown, CH 4 ebullition comprised 60–68% of emissions from floodplain ponds to the atmosphere. Using linear mixed effects modeling, we show that partial pressures of CH 4 and CO 2 and diffusive CO 2 fluxes in floodplain ponds varied on a diel basis with in situ respiration. Floodplain inundation by the Three Gorges Reservoir significantly moderated areal CH 4 diffusion and ebullition. Diel p CO 2 , p CH 4 , p N 2 O, and diffusive fluxes of CO 2 on the submerged floodplain were also driven by in situ respiration. The drawdown/inundation cycle of the Three Gorges Reservoir therefore changes the magnitudes of aquatic greenhouse gas fluxes on its floodplain.