The net GHG emissions of the Three Gorges Reservoir in China: II. Post-impoundment GHG inventories and full-scale synthesis

Abstract

Greenhouse gas (GHG) emissions are receiving worldwide attention and concern over the past decades. However, the net change of GHG emissions due to reservoir creation is not well reported. The objective of the study was to evaluate the net GHG emissions of the Three Gorges Reservoir (TGR), the largest reservoir in volume and installed capacity in China. Here, we provide the first full-scale synthesis of GHG emissions in the TGR. Data from two large sampling campaigns between 2010 and 2017 showed that the post-impoundment GHG emissions of the TGR were 1.36 ± 0.16 × 106 tCO2eq yr−1. A majority of GHGs (30%–70%) are emitted from air-water diffusive pathway in the main stem. Anthropogenic carbon and nutrients loads from the reservoir vicinity did not significantly contribute to the post-impoundment GHG emissions. Reservoir GHG emissions were mainly regulated by annual inflow. Subtracting pre-impoundment GHG emissions from post-impoundment emissions, the net GHG emissions of the TGR in our sampling campaigns were 10.41 ± 1.28 × 105 tCO2eq yr−1. In terms of CO2 equivalents per unit of hydropower production in the same years, they were 11.8 ± 1.8 gCO2eq⋅kWh−1. Mass budget analysis showed that flooding and decomposition of organic matter in flooded land could only explain 19.9% of reservoir net GHG emissions. A large proportion of the net GHG emissions needs further study to be quantitatively identified. In addition, our study elaborated the current limitations and further research needs in evaluation of carbon footprints of reservoir creation.