EAPSI: Day vs night greenhouse gas emissions from the draw-down zone of China's Three Gorges Reservoir

Miller Benjamin L, Seattle WA

Investigators

Abstract

Hydropower reservoirs emit heat-trapping gases such as carbon dioxide (CO2) and methane (CH4) like the coal-fired power plants they were designed to replace. Carbon carried by river waters settles in sediments when it enters slow-moving reservoir waters. When sediments are exposed to oxygenated water, microbes convert carbon to CO2. Without oxygen, microbes also produce CH4. Therefore, the proportions of gases produced depend on the presence of oxygen in water, which varies between day and night. Previous studies of CO2 and CH4 emissions from reservoirs have been almost exclusively conducted during the day. In collaboration with Dr. Huai Chen of the Chinese Academy of Sciences, this study will measure CO2 and CH4 emissions from one of the world's largest reservoirs, China's Three Gorges. These measurements, conducted during day and night, will contribute to a more accurate understanding of CO2 and CH4 emissions from hydropower as it expands throughout the developing world. Production of CO2 and CH4 in reservoirs varies spatially, as well as temporally. As water levels in the Three Gorges Reservoir rise and fall annually, 20% of the reservoir area around its margins is flooded and dewatered. Senesced plants in this draw-down zone are a rich and regular substrate for microbial oxidation. This study will measure diel CO2 and CH4 fluxes from the draw-down zone in dissolved and bubble form. Though studies in other reservoirs have taken similar measurements during the day, diel differences in 1) photosynthesis, which consumes CO2 and produces oxygen, 2) respiration, which consumes oxygen, and 3) atmospheric pressure, which may govern bubble release, could mean that current estimates of CO2 and CH4 fluxes in reservoirs are inaccurate. This NSF EAPSI award is funded in collaboration with the Chinese Ministry of Science and Technology.